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fuchsia / fuchsia / refs/heads/releases/dogfood / . / zircon / kernel / vm / vm_cow_pages.cc
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// Copyright 2020 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT
#include "vm/vm_cow_pages.h"
#include <lib/counters.h>
#include <trace.h>
#include <fbl/auto_call.h>
#include <kernel/range_check.h>
#include <ktl/move.h>
#include <vm/fault.h>
#include <vm/physmap.h>
#include <vm/vm_object_paged.h>
#include "vm_priv.h"
#define LOCAL_TRACE VM_GLOBAL_TRACE(0)
namespace {
void ZeroPage(paddr_t pa) {
void* ptr = paddr_to_physmap(pa);
DEBUG_ASSERT(ptr);
arch_zero_page(ptr);
}
void ZeroPage(vm_page_t* p) {
paddr_t pa = p->paddr();
ZeroPage(pa);
}
bool IsZeroPage(vm_page_t* p) {
uint64_t* base = (uint64_t*)paddr_to_physmap(p->paddr());
for (int i = 0; i < PAGE_SIZE / (int)sizeof(uint64_t); i++) {
if (base[i] != 0)
return false;
}
return true;
}
void InitializeVmPage(vm_page_t* p) {
DEBUG_ASSERT(p->state() == VM_PAGE_STATE_ALLOC);
p->set_state(VM_PAGE_STATE_OBJECT);
p->object.pin_count = 0;
p->object.cow_left_split = 0;
p->object.cow_right_split = 0;
}
// Allocates a new page and populates it with the data at |parent_paddr|.
bool AllocateCopyPage(uint32_t pmm_alloc_flags, paddr_t parent_paddr, list_node_t* alloc_list,
vm_page_t** clone) {
paddr_t pa_clone;
vm_page_t* p_clone = nullptr;
if (alloc_list) {
p_clone = list_remove_head_type(alloc_list, vm_page, queue_node);
if (p_clone) {
pa_clone = p_clone->paddr();
}
}
if (!p_clone) {
zx_status_t status = pmm_alloc_page(pmm_alloc_flags, &p_clone, &pa_clone);
if (!p_clone) {
DEBUG_ASSERT(status == ZX_ERR_NO_MEMORY);
return false;
}
DEBUG_ASSERT(status == ZX_OK);
}
InitializeVmPage(p_clone);
void* dst = paddr_to_physmap(pa_clone);
DEBUG_ASSERT(dst);
if (parent_paddr != vm_get_zero_page_paddr()) {
// do a direct copy of the two pages
const void* src = paddr_to_physmap(parent_paddr);
DEBUG_ASSERT(src);
memcpy(dst, src, PAGE_SIZE);
} else {
// avoid pointless fetches by directly zeroing dst
arch_zero_page(dst);
}
*clone = p_clone;
return true;
}
bool SlotHasPinnedPage(VmPageOrMarker* slot) {
return slot && slot->IsPage() && slot->Page()->object.pin_count > 0;
}
inline uint64_t CheckedAdd(uint64_t a, uint64_t b) {
uint64_t result;
bool overflow = add_overflow(a, b, &result);
DEBUG_ASSERT(!overflow);
return result;
}
} // namespace
// Helper class for collecting pages to performed batched Removes from the page queue to not incur
// its spinlock overhead for every single page. Pages that it removes from the page queue get placed
// into a provided list. Note that pages are not moved into the list until *after* Flush has been
// called and Flush must be called prior to object destruction.
class BatchPQRemove {
public:
BatchPQRemove(list_node_t* freed_list) : freed_list_(freed_list) {}
~BatchPQRemove() { DEBUG_ASSERT(count_ == 0); }
DISALLOW_COPY_AND_ASSIGN_ALLOW_MOVE(BatchPQRemove);
// Add a page to the batch set. Automatically calls |Flush| if the limit is reached.
void Push(vm_page_t* page) {
DEBUG_ASSERT(page);
pages_[count_] = page;
count_++;
if (count_ == kMaxPages) {
Flush();
}
}
// Performs |Remove| on any pending pages. This allows you to know that all pages are in the
// original list so that you can do operations on the list.
void Flush() {
if (count_ > 0) {
pmm_page_queues()->RemoveArrayIntoList(pages_.data(), count_, freed_list_);
count_ = 0;
}
}
// Produces a callback suitable for passing to VmPageList::RemovePages that will |Push| any pages
auto RemovePagesCallback() {
return [this](VmPageOrMarker* p, uint64_t off) {
if (p->IsPage()) {
vm_page_t* page = p->ReleasePage();
Push(page);
}
*p = VmPageOrMarker::Empty();
return ZX_ERR_NEXT;
};
}
private:
// The value of 64 was chosen as there is minimal performance gains originally measured by using
// higher values. There is an incentive on this being as small as possible due to this typically
// being created on the stack, and our stack space is limited.
static constexpr size_t kMaxPages = 64;
size_t count_ = 0;
ktl::array<vm_page_t*, kMaxPages> pages_;
list_node_t* freed_list_ = nullptr;
};
VmCowPages::VmCowPages(fbl::RefPtr<VmHierarchyState> hierarchy_state_ptr, uint32_t options,
uint32_t pmm_alloc_flags, uint64_t size, fbl::RefPtr<PageSource> page_source)
: VmHierarchyBase(ktl::move(hierarchy_state_ptr)),
options_(options),
size_(size),
pmm_alloc_flags_(pmm_alloc_flags),
page_source_(ktl::move(page_source)) {
DEBUG_ASSERT(IS_PAGE_ALIGNED(size));
}
VmCowPages::~VmCowPages() {
canary_.Assert();
// To prevent races with a hidden parent creation or merging, it is necessary to hold the lock
// over the is_hidden and parent_ check and into the subsequent removal call.
// It is safe to grab the lock here because we are careful to never cause the last reference to
// a VmCowPages to be dropped in this code whilst holding the lock. The single place we drop a
// a VmCowPages reference that could trigger a deletion is in this destructor when parent_ is
// dropped, but that is always done without holding the lock.
Guard<Mutex> guard{&lock_};
// If we're not a hidden vmo, then we need to remove ourself from our parent. This needs
// to be done before emptying the page list so that a hidden parent can't merge into this
// vmo and repopulate the page list.
if (!is_hidden_locked()) {
if (parent_) {
parent_->RemoveChildLocked(this);
guard.Release();
// Avoid recursing destructors when we delete our parent by using the deferred deletion
// method. See common in parent else branch for why we can avoid this on a hidden parent.
if (!parent_->is_hidden_locked()) {
hierarchy_state_ptr_->DoDeferredDelete(ktl::move(parent_));
}
}
} else {
// Most of the hidden vmo's state should have already been cleaned up when it merged
// itself into its child in ::RemoveChildLocked.
DEBUG_ASSERT(children_list_len_ == 0);
DEBUG_ASSERT(page_list_.HasNoPages());
// Even though we are hidden we might have a parent. Unlike in the other branch of this if we
// do not need to perform any deferred deletion. The reason for this is that the deferred
// deletion mechanism is intended to resolve the scenario where there is a chain of 'one ref'
// parent pointers that will chain delete. However, with hidden parents we *know* that a hidden
// parent has two children (and hence at least one other ref to it) and so we cannot be in a
// one ref chain. Even if N threads all tried to remove children from the hierarchy at once,
// this would ultimately get serialized through the lock and the hierarchy would go from
//
// [..]
// /
// A [..]
// / \ /
// B E TO B A
// / \ / / \.
// C D C D E
//
// And so each serialized deletion breaks of a discrete two VMO chain that can be safely
// finalized with one recursive step.
}
// Cleanup page lists and page sources.
list_node_t list;
list_initialize(&list);
BatchPQRemove page_remover(&list);
// free all of the pages attached to us
page_list_.RemoveAllPages([&page_remover](vm_page_t* page) {
ASSERT(page->object.pin_count == 0);
page_remover.Push(page);
});
if (page_source_) {
page_source_->Close();
}
page_remover.Flush();
pmm_free(&list);
}
bool VmCowPages::DedupZeroPage(vm_page_t* page, uint64_t offset) {
canary_.Assert();
Guard<Mutex> guard{&lock_};
if (paged_ref_) {
AssertHeld(paged_ref_->lock_ref());
if (!paged_ref_->CanDedupZeroPagesLocked()) {
return false;
}
}
// Check this page is still a part of this VMO. object.page_offset could be complete garbage,
// but there's no harm in looking up a random slot as we'll then notice it's the wrong page.
VmPageOrMarker* page_or_marker = page_list_.Lookup(offset);
if (!page_or_marker || !page_or_marker->IsPage() || page_or_marker->Page() != page ||
page->object.pin_count > 0) {
return false;
}
// We expect most pages to not be zero, as such we will first do a 'racy' zero page check where
// we leave write permissions on the page. If the page isn't zero, which is our hope, then we
// haven't paid the price of modifying page tables.
if (!IsZeroPage(page_or_marker->Page())) {
return false;
}
RangeChangeUpdateLocked(offset, PAGE_SIZE, RangeChangeOp::RemoveWrite);
if (IsZeroPage(page_or_marker->Page())) {
RangeChangeUpdateLocked(offset, PAGE_SIZE, RangeChangeOp::Unmap);
vm_page_t* page = page_or_marker->ReleasePage();
pmm_page_queues()->Remove(page);
DEBUG_ASSERT(!list_in_list(&page->queue_node));
pmm_free_page(page);
*page_or_marker = VmPageOrMarker::Marker();
eviction_event_count_++;
IncrementHierarchyGenerationCountLocked();
return true;
}
return false;
}
uint32_t VmCowPages::ScanForZeroPagesLocked(bool reclaim) {
canary_.Assert();
// Check if we have any slice children. Slice children may have writable mappings to our pages,
// and so we need to also remove any mappings from them. Non-slice children could only have
// read-only mappings, which is the state we already want, and so we don't need to touch them.
for (auto& child : children_list_) {
AssertHeld(child.lock_);
if (child.is_slice_locked()) {
// Slices are strict subsets of their parents so we don't need to bother looking at parent
// limits etc and can just operate on the entire range.
child.RangeChangeUpdateLocked(0, child.size_, RangeChangeOp::RemoveWrite);
}
}
list_node_t freed_list;
list_initialize(&freed_list);
uint32_t count = 0;
page_list_.RemovePages(
[&count, &freed_list, reclaim, this](VmPageOrMarker* p, uint64_t off) {
// Pinned pages cannot be decommitted so do not consider them.
if (p->IsPage() && p->Page()->object.pin_count == 0 && IsZeroPage(p->Page())) {
count++;
if (reclaim) {
// Need to remove all mappings (include read) ones to this range before we remove the
// page.
AssertHeld(this->lock_);
RangeChangeUpdateLocked(off, PAGE_SIZE, RangeChangeOp::Unmap);
vm_page_t* page = p->ReleasePage();
pmm_page_queues()->Remove(page);
DEBUG_ASSERT(!list_in_list(&page->queue_node));
list_add_tail(&freed_list, &page->queue_node);
*p = VmPageOrMarker::Marker();
}
}
return ZX_ERR_NEXT;
},
0, VmPageList::MAX_SIZE);
pmm_free(&freed_list);
return count;
}
zx_status_t VmCowPages::Create(fbl::RefPtr<VmHierarchyState> root_lock, uint32_t pmm_alloc_flags,
uint64_t size, fbl::RefPtr<VmCowPages>* cow_pages) {
fbl::AllocChecker ac;
auto cow = fbl::AdoptRef<VmCowPages>(
new (&ac) VmCowPages(ktl::move(root_lock), 0, pmm_alloc_flags, size, nullptr));
if (!ac.check()) {
return ZX_ERR_NO_MEMORY;
}
*cow_pages = ktl::move(cow);
return ZX_OK;
}
zx_status_t VmCowPages::CreateExternal(fbl::RefPtr<PageSource> src,
fbl::RefPtr<VmHierarchyState> root_lock, uint64_t size,
fbl::RefPtr<VmCowPages>* cow_pages) {
fbl::AllocChecker ac;
auto cow = fbl::AdoptRef<VmCowPages>(
new (&ac) VmCowPages(ktl::move(root_lock), 0, PMM_ALLOC_FLAG_ANY, size, ktl::move(src)));
if (!ac.check()) {
return ZX_ERR_NO_MEMORY;
}
*cow_pages = ktl::move(cow);
return ZX_OK;
}
void VmCowPages::ReplaceChildLocked(VmCowPages* old, VmCowPages* new_child) {
canary_.Assert();
children_list_.replace(*old, new_child);
}
void VmCowPages::DropChildLocked(VmCowPages* child) {
canary_.Assert();
DEBUG_ASSERT(children_list_len_ > 0);
children_list_.erase(*child);
--children_list_len_;
}
void VmCowPages::AddChildLocked(VmCowPages* child, uint64_t offset, uint64_t root_parent_offset,
uint64_t parent_limit) {
canary_.Assert();
// As we do not want to have to return failure from this function we require root_parent_offset to
// be calculated and validated that it does not overflow externally, but we can still assert that
// it has been calculated correctly to prevent accidents.
AssertHeld(child->lock_ref());
DEBUG_ASSERT(CheckedAdd(root_parent_offset_, offset) == root_parent_offset);
// The child should definitely stop seeing into the parent at the limit of its size.
DEBUG_ASSERT(parent_limit <= child->size_);
// Write in the parent view values.
child->root_parent_offset_ = root_parent_offset;
child->parent_offset_ = offset;
child->parent_limit_ = parent_limit;
// This child should be in an initial state and these members should be clear.
DEBUG_ASSERT(!child->partial_cow_release_);
DEBUG_ASSERT(child->parent_start_limit_ == 0);
child->page_list_.InitializeSkew(page_list_.GetSkew(), offset);
child->parent_ = fbl::RefPtr(this);
children_list_.push_front(child);
children_list_len_++;
}
zx_status_t VmCowPages::CreateChildSliceLocked(uint64_t offset, uint64_t size,
fbl::RefPtr<VmCowPages>* cow_slice) {
LTRACEF("vmo %p offset %#" PRIx64 " size %#" PRIx64 "\n", this, offset, size);
canary_.Assert();
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(size));
DEBUG_ASSERT(CheckedAdd(offset, size) <= size_);
// If this is a slice re-home this on our parent. Due to this logic we can guarantee that any
// slice parent is, itself, not a slice.
// We are able to do this for two reasons:
// * Slices are subsets and so every position in a slice always maps back to the paged parent.
// * Slices are not permitted to be resized and so nothing can be done on the intermediate parent
// that requires us to ever look at it again.
if (is_slice_locked()) {
DEBUG_ASSERT(parent_);
AssertHeld(parent_->lock_ref());
DEBUG_ASSERT(!parent_->is_slice_locked());
return parent_->CreateChildSliceLocked(offset + parent_offset_, size, cow_slice);
}
fbl::AllocChecker ac;
// Slices just need the slice option and default alloc flags since they will propagate any
// operation up to a parent and use their options and alloc flags.
auto slice = fbl::AdoptRef<VmCowPages>(
new (&ac) VmCowPages(hierarchy_state_ptr_, kSlice, PMM_ALLOC_FLAG_ANY, size, nullptr));
if (!ac.check()) {
return ZX_ERR_NO_MEMORY;
}
// At this point slice must *not* be destructed in this function, as doing so would cause a
// deadlock. That means from this point on we *must* succeed and any future error checking needs
// to be added prior to creation.
AssertHeld(slice->lock_);
// As our slice must be in range of the parent it is impossible to have the accumulated parent
// offset overflow.
uint64_t root_parent_offset = CheckedAdd(offset, root_parent_offset_);
CheckedAdd(root_parent_offset, size);
AddChildLocked(slice.get(), offset, root_parent_offset, size);
*cow_slice = slice;
return ZX_OK;
}
void VmCowPages::CloneParentIntoChildLocked(fbl::RefPtr<VmCowPages>& child) {
AssertHeld(child->lock_ref());
// This function is invalid to call if any pages are pinned as the unpin after we change the
// backlink will not work.
DEBUG_ASSERT(pinned_page_count_ == 0);
// We are going to change our linked VmObjectPaged to eventually point to our left child instead
// of us, so we need to make the left child look equivalent. To do this it inherits our
// children, attribution id and eviction count and is sized to completely cover us.
for (auto& c : children_list_) {
AssertHeld(c.lock_ref());
c.parent_ = child;
}
child->children_list_ = ktl::move(children_list_);
child->children_list_len_ = children_list_len_;
children_list_len_ = 0;
child->eviction_event_count_ = eviction_event_count_;
child->page_attribution_user_id_ = page_attribution_user_id_;
AddChildLocked(child.get(), 0, root_parent_offset_, size_);
// Time to change the VmCowPages that our paged_ref_ is point to.
if (paged_ref_) {
child->paged_ref_ = paged_ref_;
AssertHeld(paged_ref_->lock_ref());
fbl::RefPtr<VmCowPages> __UNUSED previous =
paged_ref_->SetCowPagesReferenceLocked(ktl::move(child));
// Validate that we replaced a reference to ourself as we expected, this ensures we can safely
// drop the refptr without triggering our own destructor, since we know someone else must be
// holding a refptr to us to be in this function.
DEBUG_ASSERT(previous.get() == this);
paged_ref_ = nullptr;
}
}
zx_status_t VmCowPages::CreateCloneLocked(CloneType type, uint64_t offset, uint64_t size,
fbl::RefPtr<VmCowPages>* cow_child) {
LTRACEF("vmo %p offset %#" PRIx64 " size %#" PRIx64 "\n", this, offset, size);
canary_.Assert();
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(size));
DEBUG_ASSERT(!is_hidden_locked());
// All validation *must* be performed here prior to construction the VmCowPages, as the
// destructor for VmCowPages may acquire the lock, which we are already holding.
switch (type) {
case CloneType::Snapshot: {
if (!IsCowClonableLocked()) {
return ZX_ERR_NOT_SUPPORTED;
}
// If this is non-zero, that means that there are pages which hardware can
// touch, so the vmo can't be safely cloned.
// TODO: consider immediately forking these pages.
if (pinned_page_count_locked()) {
return ZX_ERR_BAD_STATE;
}
break;
}
case CloneType::PrivatePagerCopy:
if (!is_pager_backed_locked()) {
return ZX_ERR_NOT_SUPPORTED;
}
break;
}
uint64_t new_root_parent_offset;
bool overflow;
overflow = add_overflow(offset, root_parent_offset_, &new_root_parent_offset);
if (overflow) {
return ZX_ERR_INVALID_ARGS;
}
uint64_t temp;
overflow = add_overflow(new_root_parent_offset, size, &temp);
if (overflow) {
return ZX_ERR_INVALID_ARGS;
}
uint64_t child_parent_limit = offset >= size_ ? 0 : ktl::min(size, size_ - offset);
// Invalidate everything the clone will be able to see. They're COW pages now,
// so any existing mappings can no longer directly write to the pages.
RangeChangeUpdateLocked(offset, size, RangeChangeOp::RemoveWrite);
if (type == CloneType::Snapshot) {
// We need two new VmCowPages for our two children. To avoid destructor of the first being
// invoked if the second fails we separately perform allocations and construction.
union VmCowPagesPlaceHolder {
VmCowPagesPlaceHolder() {}
~VmCowPagesPlaceHolder() {}
uint8_t trivially_destructible_default_variant;
VmCowPages vm_cow_pages;
};
fbl::AllocChecker ac;
ktl::unique_ptr<VmCowPagesPlaceHolder> left_child_placeholder =
ktl::make_unique<VmCowPagesPlaceHolder>(&ac);
if (!ac.check()) {
return ZX_ERR_NO_MEMORY;
}
ktl::unique_ptr<VmCowPagesPlaceHolder> right_child_placeholder =
ktl::make_unique<VmCowPagesPlaceHolder>(&ac);
if (!ac.check()) {
return ZX_ERR_NO_MEMORY;
}
// At this point cow_pages must *not* be destructed in this function, as doing so would cause a
// deadlock. That means from this point on we *must* succeed and any future error checking needs
// to be added prior to creation.
fbl::RefPtr<VmCowPages> left_child =
fbl::AdoptRef<VmCowPages>(new (&left_child_placeholder.release()->vm_cow_pages) VmCowPages(
hierarchy_state_ptr_, 0, pmm_alloc_flags_, size_, nullptr));
fbl::RefPtr<VmCowPages> right_child =
fbl::AdoptRef<VmCowPages>(new (&right_child_placeholder.release()->vm_cow_pages) VmCowPages(
hierarchy_state_ptr_, 0, pmm_alloc_flags_, size, nullptr));
AssertHeld(left_child->lock_ref());
AssertHeld(right_child->lock_ref());
// The left child becomes a full clone of us, inheriting our children, paged backref etc.
CloneParentIntoChildLocked(left_child);
// The right child is the, potential, subset view into the parent so has a variable offset. If
// this view would extend beyond us then we need to clip the parent_limit to our size_, which
// will ensure any pages in that range just get initialized from zeroes.
AddChildLocked(right_child.get(), offset, new_root_parent_offset, child_parent_limit);
// Transition into being the hidden node.
options_ |= kHidden;
DEBUG_ASSERT(children_list_len_ == 2);
*cow_child = ktl::move(right_child);
return ZX_OK;
} else {
fbl::AllocChecker ac;
auto cow_pages = fbl::AdoptRef<VmCowPages>(
new (&ac) VmCowPages(hierarchy_state_ptr_, 0, pmm_alloc_flags_, size, nullptr));
if (!ac.check()) {
return ZX_ERR_NO_MEMORY;
}
// Walk up the parent chain until we find a good place to hang this new cow clone. A good place
// here means the first place that has committed pages that we actually need to snapshot. In
// doing so we need to ensure that the limits of the child we create do not end up seeing more
// of the final parent than it would have been able to see from here.
VmCowPages* cur = this;
AssertHeld(cur->lock_ref());
while (cur->parent_) {
// There's a parent, check if there are any pages in the current range. Unless we've moved
// outside the range of our parent, in which case we can just walk up.
if (child_parent_limit > 0 &&
cur->page_list_.AnyPagesInRange(offset, offset + child_parent_limit)) {
break;
}
// To move to the parent we need to translate our window into |cur|.
if (offset >= cur->parent_limit_) {
child_parent_limit = 0;
} else {
child_parent_limit = ktl::min(child_parent_limit, cur->parent_limit_ - offset);
}
offset += cur->parent_offset_;
cur = cur->parent_.get();
}
new_root_parent_offset = CheckedAdd(offset, cur->root_parent_offset_);
cur->AddChildLocked(cow_pages.get(), offset, new_root_parent_offset, child_parent_limit);
*cow_child = ktl::move(cow_pages);
}
return ZX_OK;
}
void VmCowPages::RemoveChildLocked(VmCowPages* removed) {
canary_.Assert();
AssertHeld(removed->lock_);
if (!is_hidden_locked()) {
DropChildLocked(removed);
return;
}
// Hidden vmos always have 0 or 2 children, but we can't be here with 0 children.
DEBUG_ASSERT(children_list_len_ == 2);
bool removed_left = &left_child_locked() == removed;
DropChildLocked(removed);
VmCowPages* child = &children_list_.front();
DEBUG_ASSERT(child);
MergeContentWithChildLocked(removed, removed_left);
// The child which removed itself and led to the invocation should have a reference
// to us, in addition to child.parent_ which we are about to clear.
DEBUG_ASSERT(ref_count_debug() >= 2);
AssertHeld(child->lock_);
if (child->page_attribution_user_id_ != page_attribution_user_id_) {
// If the attribution user id of this vmo doesn't match that of its remaining child,
// then the vmo with the matching attribution user id was just closed. In that case, we
// need to reattribute the pages of any ancestor hidden vmos to vmos that still exist.
//
// The syscall API doesn't specify how pages are to be attributed among a group of COW
// clones. One option is to pick a remaining vmo 'arbitrarily' and attribute everything to
// that vmo. However, it seems fairer to reattribute each remaining hidden vmo with
// its child whose user id doesn't match the vmo that was just closed. So walk up the
// clone chain and attribute each hidden vmo to the vmo we didn't just walk through.
auto cur = this;
AssertHeld(cur->lock_);
uint64_t user_id_to_skip = page_attribution_user_id_;
while (cur->parent_ != nullptr) {
auto parent = cur->parent_.get();
AssertHeld(parent->lock_);
DEBUG_ASSERT(parent->is_hidden_locked());
if (parent->page_attribution_user_id_ == page_attribution_user_id_) {
uint64_t new_user_id = parent->left_child_locked().page_attribution_user_id_;
if (new_user_id == user_id_to_skip) {
new_user_id = parent->right_child_locked().page_attribution_user_id_;
}
// Although user IDs can be unset for VMOs that do not have a dispatcher, copy-on-write
// VMOs always have user level dispatchers, and should have a valid user-id set, hence we
// should never end up re-attributing a hidden parent with an unset id.
DEBUG_ASSERT(new_user_id != 0);
// The 'if' above should mean that the new_user_id isn't the ID we are trying to remove
// and isn't one we just used. For this to fail we either need a corrupt VMO hierarchy, or
// to have labeled two leaf nodes with the same user_id, which would also be incorrect as
// leaf nodes have unique dispatchers and hence unique ids.
DEBUG_ASSERT(new_user_id != page_attribution_user_id_ && new_user_id != user_id_to_skip);
parent->page_attribution_user_id_ = new_user_id;
user_id_to_skip = new_user_id;
cur = parent;
} else {
break;
}
}
}
// Drop the child from our list, but don't recurse back into this function. Then
// remove ourselves from the clone tree.
DropChildLocked(child);
if (parent_) {
AssertHeld(parent_->lock_ref());
parent_->ReplaceChildLocked(this, child);
}
child->parent_ = ktl::move(parent_);
}
void VmCowPages::MergeContentWithChildLocked(VmCowPages* removed, bool removed_left) {
DEBUG_ASSERT(children_list_len_ == 1);
VmCowPages& child = children_list_.front();
AssertHeld(child.lock_);
AssertHeld(removed->lock_);
list_node freed_pages;
list_initialize(&freed_pages);
BatchPQRemove page_remover(&freed_pages);
const uint64_t visibility_start_offset = child.parent_offset_ + child.parent_start_limit_;
const uint64_t merge_start_offset = child.parent_offset_;
const uint64_t merge_end_offset = child.parent_offset_ + child.parent_limit_;
// Hidden parents are not supposed to have page sources, but we assert it here anyway because a
// page source would make the way we move pages between objects incorrect, as we would break any
// potential back links.
DEBUG_ASSERT(!page_source_);
page_list_.RemovePages(page_remover.RemovePagesCallback(), 0, visibility_start_offset);
page_list_.RemovePages(page_remover.RemovePagesCallback(), merge_end_offset,
VmPageList::MAX_SIZE);
if (child.parent_offset_ + child.parent_limit_ > parent_limit_) {
// Update the child's parent limit to ensure that it won't be able to see more
// of its new parent than this hidden vmo was able to see.
if (parent_limit_ < child.parent_offset_) {
child.parent_limit_ = 0;
child.parent_start_limit_ = 0;
} else {
child.parent_limit_ = parent_limit_ - child.parent_offset_;
child.parent_start_limit_ = ktl::min(child.parent_start_limit_, child.parent_limit_);
}
} else {
// The child will be able to see less of its new parent than this hidden vmo was
// able to see, so release any parent pages in that range.
ReleaseCowParentPagesLocked(merge_end_offset, parent_limit_, &page_remover);
}
if (removed->parent_offset_ + removed->parent_start_limit_ < visibility_start_offset) {
// If the removed former child has a smaller offset, then there are retained
// ancestor pages that will no longer be visible and thus should be freed.
ReleaseCowParentPagesLocked(removed->parent_offset_ + removed->parent_start_limit_,
visibility_start_offset, &page_remover);
}
// Adjust the child's offset so it will still see the correct range.
bool overflow = add_overflow(parent_offset_, child.parent_offset_, &child.parent_offset_);
// Overflow here means that something went wrong when setting up parent limits.
DEBUG_ASSERT(!overflow);
if (child.is_hidden_locked()) {
// After the merge, either |child| can't see anything in parent (in which case
// the parent limits could be anything), or |child|'s first visible offset will be
// at least as large as |this|'s first visible offset.
DEBUG_ASSERT(child.parent_start_limit_ == child.parent_limit_ ||
parent_offset_ + parent_start_limit_ <=
child.parent_offset_ + child.parent_start_limit_);
} else {
// non-hidden vmos should always have zero parent_start_limit_
DEBUG_ASSERT(child.parent_start_limit_ == 0);
}
// As we are moving pages between objects we need to make sure no backlinks are broken. We know
// there's no page_source_ and hence no pages will be in the pager_backed queue, but we could
// have pages in the unswappable_zero_forked queue. We do know that pages in this queue cannot
// have been pinned, so we can just move (or re-move potentially) any page that is not pinned
// into the unswappable queue.
{
PageQueues* pq = pmm_page_queues();
Guard<SpinLock, IrqSave> guard{pq->get_lock()};
page_list_.ForEveryPage([pq](auto* p, uint64_t off) {
if (p->IsPage()) {
vm_page_t* page = p->Page();
if (page->object.pin_count == 0) {
AssertHeld<Lock<SpinLock>, IrqSave>(*pq->get_lock());
pq->MoveToUnswappableLocked(page);
}
}
return ZX_ERR_NEXT;
});
}
// At this point, we need to merge |this|'s page list and |child|'s page list.
//
// In general, COW clones are expected to share most of their pages (i.e. to fork a relatively
// small number of pages). Because of this, it is preferable to do work proportional to the
// number of pages which were forked into |removed|. However, there are a few things that can
// prevent this:
// - If |child|'s offset is non-zero then the offsets of all of |this|'s pages will
// need to be updated when they are merged into |child|.
// - If there has been a call to ReleaseCowParentPagesLocked which was not able to
// update the parent limits, then there can exist pages in this vmo's page list
// which are not visible to |child| but can't be easily freed based on its parent
// limits. Finding these pages requires examining the split bits of all pages.
// - If |child| is hidden, then there can exist pages in this vmo which were split into
// |child|'s subtree and then migrated out of |child|. Those pages need to be freed, and
// the simplest way to find those pages is to examine the split bits.
bool fast_merge = merge_start_offset == 0 && !partial_cow_release_ && !child.is_hidden_locked();
if (fast_merge) {
// Only leaf vmos can be directly removed, so this must always be true. This guarantees
// that there are no pages that were split into |removed| that have since been migrated
// to its children.
DEBUG_ASSERT(!removed->is_hidden_locked());
// Before merging, find any pages that are present in both |removed| and |this|. Those
// pages are visibile to |child| but haven't been written to through |child|, so
// their split bits need to be cleared. Note that ::ReleaseCowParentPagesLocked ensures
// that pages outside of the parent limit range won't have their split bits set.
removed->page_list_.ForEveryPageInRange(
[removed_offset = removed->parent_offset_, this](auto* page, uint64_t offset) {
AssertHeld(lock_);
if (page->IsMarker()) {
return ZX_ERR_NEXT;
}
VmPageOrMarker* page_or_mark = page_list_.Lookup(offset + removed_offset);
if (page_or_mark && page_or_mark->IsPage()) {
vm_page* p_page = page_or_mark->Page();
// The page is definitely forked into |removed|, but
// shouldn't be forked twice.
DEBUG_ASSERT(p_page->object.cow_left_split ^ p_page->object.cow_right_split);
p_page->object.cow_left_split = 0;
p_page->object.cow_right_split = 0;
}
return ZX_ERR_NEXT;
},
removed->parent_start_limit_, removed->parent_limit_);
list_node covered_pages;
list_initialize(&covered_pages);
BatchPQRemove covered_remover(&covered_pages);
// Now merge |child|'s pages into |this|, overwriting any pages present in |this|, and
// then move that list to |child|.
child.page_list_.MergeOnto(page_list_,
[&covered_remover](vm_page_t* p) { covered_remover.Push(p); });
child.page_list_ = ktl::move(page_list_);
vm_page_t* p;
covered_remover.Flush();
list_for_every_entry (&covered_pages, p, vm_page_t, queue_node) {
// The page was already present in |child|, so it should be split at least
// once. And being split twice is obviously bad.
ASSERT(p->object.cow_left_split ^ p->object.cow_right_split);
ASSERT(p->object.pin_count == 0);
}
list_splice_after(&covered_pages, &freed_pages);
} else {
// Merge our page list into the child page list and update all the necessary metadata.
child.page_list_.MergeFrom(
page_list_, merge_start_offset, merge_end_offset,
[&page_remover](vm_page* page, uint64_t offset) { page_remover.Push(page); },
[&page_remover, removed_left](VmPageOrMarker* page_or_marker, uint64_t offset) {
DEBUG_ASSERT(page_or_marker->IsPage());
vm_page_t* page = page_or_marker->Page();
DEBUG_ASSERT(page->object.pin_count == 0);
if (removed_left ? page->object.cow_right_split : page->object.cow_left_split) {
// This happens when the pages was already migrated into child but then
// was migrated further into child's descendants. The page can be freed.
page = page_or_marker->ReleasePage();
page_remover.Push(page);
} else {
// Since we recursively fork on write, if the child doesn't have the
// page, then neither of its children do.
page->object.cow_left_split = 0;
page->object.cow_right_split = 0;
}
});
}
page_remover.Flush();
if (!list_is_empty(&freed_pages)) {
pmm_free(&freed_pages);
}
}
void VmCowPages::DumpLocked(uint depth, bool verbose) const {
canary_.Assert();
size_t count = 0;
page_list_.ForEveryPage([&count](const auto* p, uint64_t) {
if (p->IsPage()) {
count++;
}
return ZX_ERR_NEXT;
});
for (uint i = 0; i < depth; ++i) {
printf(" ");
}
printf("cow_pages %p size %#" PRIx64 " offset %#" PRIx64 " start limit %#" PRIx64
" limit %#" PRIx64 " pages %zu ref %d parent %p\n",
this, size_, parent_offset_, parent_start_limit_, parent_limit_, count, ref_count_debug(),
parent_.get());
if (page_source_) {
for (uint i = 0; i < depth + 1; ++i) {
printf(" ");
}
page_source_->Dump();
}
if (verbose) {
auto f = [depth](const auto* p, uint64_t offset) {
for (uint i = 0; i < depth + 1; ++i) {
printf(" ");
}
if (p->IsMarker()) {
printf("offset %#" PRIx64 " zero page marker\n", offset);
} else {
vm_page_t* page = p->Page();
printf("offset %#" PRIx64 " page %p paddr %#" PRIxPTR "(%c%c)\n", offset, page,
page->paddr(), page->object.cow_left_split ? 'L' : '.',
page->object.cow_right_split ? 'R' : '.');
}
return ZX_ERR_NEXT;
};
page_list_.ForEveryPage(f);
}
}
size_t VmCowPages::AttributedPagesInRangeLocked(uint64_t offset, uint64_t len) const {
canary_.Assert();
if (is_hidden_locked()) {
return 0;
}
size_t page_count = 0;
// TODO: Decide who pages should actually be attribtued to.
page_list_.ForEveryPageAndGapInRange(
[&page_count](const auto* p, uint64_t off) {
if (p->IsPage()) {
page_count++;
}
return ZX_ERR_NEXT;
},
[this, &page_count](uint64_t gap_start, uint64_t gap_end) {
AssertHeld(lock_);
// If there's no parent, there's no pages to care about. If there is a non-hidden
// parent, then that owns any pages in the gap, not us.
if (!parent_) {
return ZX_ERR_NEXT;
}
AssertHeld(parent_->lock_ref());
if (!parent_->is_hidden_locked()) {
return ZX_ERR_NEXT;
}
// Count any ancestor pages that should be attributed to us in the range. Ideally the whole
// range gets processed in one attempt, but in order to prevent unbounded stack growth with
// recursion we instead process partial ranges and recalculate the intermediate results.
// As a result instead of being O(n) in the number of committed pages it could
// pathologically become O(nd) where d is our depth in the vmo hierarchy.
uint64_t off = gap_start;
while (off < parent_limit_ && off < gap_end) {
uint64_t local_count = 0;
uint64_t attributed =
CountAttributedAncestorPagesLocked(off, gap_end - off, &local_count);
// |CountAttributedAncestorPagesLocked| guarantees that it will make progress.
DEBUG_ASSERT(attributed > 0);
off += attributed;
page_count += local_count;
}
return ZX_ERR_NEXT;
},
offset, offset + len);
return page_count;
}
uint64_t VmCowPages::CountAttributedAncestorPagesLocked(uint64_t offset, uint64_t size,
uint64_t* count) const TA_REQ(lock_) {
// We need to walk up the ancestor chain to see if there are any pages that should be attributed
// to this vmo. We attempt operate on the entire range given to us but should we need to query
// the next parent for a range we trim our operating range. Trimming the range is necessary as
// we cannot recurse and otherwise have no way to remember where we were up to after processing
// the range in the parent. The solution then is to return all the way back up to the caller with
// a partial range and then effectively recompute the meta data at the point we were up to.
// Note that we cannot stop just because the page_attribution_user_id_ changes. This is because
// there might still be a forked page at the offset in question which should be attributed to
// this vmo. Whenever the attribution user id changes while walking up the ancestors, we need
// to determine if there is a 'closer' vmo in the sibling subtree to which the offset in
// question can be attributed, or if it should still be attributed to the current vmo.
DEBUG_ASSERT(offset < parent_limit_);
const VmCowPages* cur = this;
AssertHeld(cur->lock_);
uint64_t cur_offset = offset;
uint64_t cur_size = size;
// Count of how many pages we attributed as being owned by this vmo.
uint64_t attributed_ours = 0;
// Count how much we've processed. This is needed to remember when we iterate up the parent list
// at an offset.
uint64_t attributed = 0;
while (cur_offset < cur->parent_limit_) {
// For cur->parent_limit_ to be non-zero, it must have a parent.
DEBUG_ASSERT(cur->parent_);
const auto parent = cur->parent_.get();
AssertHeld(parent->lock_);
uint64_t parent_offset;
bool overflowed = add_overflow(cur->parent_offset_, cur_offset, &parent_offset);
DEBUG_ASSERT(!overflowed); // vmo creation should have failed
DEBUG_ASSERT(parent_offset <= parent->size_); // parent_limit_ prevents this
const bool left = cur == &parent->left_child_locked();
const auto& sib = left ? parent->right_child_locked() : parent->left_child_locked();
// Work out how much of the desired size is actually visible to us in the parent, we just use
// this to walk the correct amount of the page_list_
const uint64_t parent_size = ktl::min(cur_size, cur->parent_limit_ - cur_offset);
// By default we expect to process the entire range, hence our next_size is 0. Should we need to
// iterate up the stack then these will be set by one of the callbacks.
uint64_t next_parent_offset = parent_offset + cur_size;
uint64_t next_size = 0;
parent->page_list_.ForEveryPageAndGapInRange(
[&parent, &cur, &attributed_ours, &sib](const auto* p, uint64_t off) {
AssertHeld(cur->lock_);
AssertHeld(sib.lock_);
AssertHeld(parent->lock_);
if (p->IsMarker()) {
return ZX_ERR_NEXT;
}
vm_page* page = p->Page();
if (
// Page is explicitly owned by us
(parent->page_attribution_user_id_ == cur->page_attribution_user_id_) ||
// If page has already been split and we can see it, then we know
// the sibling subtree can't see the page and thus it should be
// attributed to this vmo.
(page->object.cow_left_split || page->object.cow_right_split) ||
// If the sibling cannot access this page then its ours, otherwise we know there's
// a vmo in the sibling subtree which is 'closer' to this offset, and to which we will
// attribute the page to.
!(sib.parent_offset_ + sib.parent_start_limit_ <= off &&
off < sib.parent_offset_ + sib.parent_limit_)) {
attributed_ours++;
}
return ZX_ERR_NEXT;
},
[&parent, &cur, &next_parent_offset, &next_size, &sib](uint64_t gap_start,
uint64_t gap_end) {
// Process a gap in the parent VMO.
//
// A gap in the parent VMO doesn't necessarily mean there are no pages
// in this range: our parent's ancestors may have pages, so we need to
// walk up the tree to find out.
//
// We don't always need to walk the tree though: in this this gap, both this VMO
// and our sibling VMO will share the same set of ancestor pages. However, the
// pages will only be accounted to one of the two VMOs.
//
// If the parent page_attribution_user_id is the same as us, we need to
// keep walking up the tree to perform a more accurate count.
//
// If the parent page_attribution_user_id is our sibling, however, we
// can just ignore the overlapping range: pages may or may not exist in
// the range --- but either way, they would be accounted to our sibling.
// Instead, we need only walk up ranges not visible to our sibling.
AssertHeld(cur->lock_);
AssertHeld(sib.lock_);
AssertHeld(parent->lock_);
uint64_t gap_size = gap_end - gap_start;
if (parent->page_attribution_user_id_ == cur->page_attribution_user_id_) {
// don't need to consider siblings as we own this range, but we do need to
// keep looking up the stack to find any actual pages.
next_parent_offset = gap_start;
next_size = gap_size;
return ZX_ERR_STOP;
}
// For this entire range we know that the offset is visible to the current vmo, and there
// are no committed or migrated pages. We need to check though for what portion of this
// range we should attribute to the sibling. Any range that we can attribute to the
// sibling we can skip, otherwise we have to keep looking up the stack to see if there are
// any pages that could be attributed to us.
uint64_t sib_offset, sib_len;
if (!GetIntersect(gap_start, gap_size, sib.parent_offset_ + sib.parent_start_limit_,
sib.parent_limit_ - sib.parent_start_limit_, &sib_offset, &sib_len)) {
// No sibling ownership, so need to look at the whole range in the parent to find any
// pages.
next_parent_offset = gap_start;
next_size = gap_size;
return ZX_ERR_STOP;
}
// If the whole range is owned by the sibling, any pages that might be in
// it won't be accounted to us anyway. Skip the segment.
if (sib_len == gap_size) {
DEBUG_ASSERT(sib_offset == gap_start);
return ZX_ERR_NEXT;
}
// Otherwise, inspect the range not visible to our sibling.
if (sib_offset == gap_start) {
next_parent_offset = sib_offset + sib_len;
next_size = gap_end - next_parent_offset;
} else {
next_parent_offset = gap_start;
next_size = sib_offset - gap_start;
}
return ZX_ERR_STOP;
},
parent_offset, parent_offset + parent_size);
if (next_size == 0) {
// If next_size wasn't set then we don't need to keep looking up the chain as we successfully
// looked at the entire range.
break;
}
// Count anything up to the next starting point as being processed.
attributed += next_parent_offset - parent_offset;
// Size should have been reduced by at least the amount we just attributed
DEBUG_ASSERT(next_size <= cur_size &&
cur_size - next_size >= next_parent_offset - parent_offset);
cur = parent;
cur_offset = next_parent_offset;
cur_size = next_size;
}
// Exiting the loop means we either ceased finding a relevant parent for the range, or we were
// able to process the entire range without needing to look up to a parent, in either case we
// can consider the entire range as attributed.
//
// The cur_size can be larger than the value of parent_size from the last loop iteration. This is
// fine as that range we trivially know has zero pages in it, and therefore has zero pages to
// determine attributions off.
attributed += cur_size;
*count = attributed_ours;
return attributed;
}
zx_status_t VmCowPages::AddPageLocked(VmPageOrMarker* p, uint64_t offset, bool do_range_update) {
canary_.Assert();
if (p->IsPage()) {
LTRACEF("vmo %p, offset %#" PRIx64 ", page %p (%#" PRIxPTR ")\n", this, offset, p->Page(),
p->Page()->paddr());
} else {
DEBUG_ASSERT(p->IsMarker());
LTRACEF("vmo %p, offset %#" PRIx64 ", marker\n", this, offset);
}
if (offset >= size_) {
return ZX_ERR_OUT_OF_RANGE;
}
VmPageOrMarker* page = page_list_.LookupOrAllocate(offset);
if (!page) {
return ZX_ERR_NO_MEMORY;
}
// Only fail on pages, we overwrite markers and empty slots.
if (page->IsPage()) {
return ZX_ERR_ALREADY_EXISTS;
}
// If this is actually a real page, we need to place it into the appropriate queue.
if (p->IsPage()) {
vm_page_t* page = p->Page();
DEBUG_ASSERT(page->state() == VM_PAGE_STATE_OBJECT);
DEBUG_ASSERT(page->object.pin_count == 0);
SetNotWired(page, offset);
}
*page = ktl::move(*p);
if (do_range_update) {
// other mappings may have covered this offset into the vmo, so unmap those ranges
RangeChangeUpdateLocked(offset, PAGE_SIZE, RangeChangeOp::Unmap);
}
return ZX_OK;
}
zx_status_t VmCowPages::AddNewPageLocked(uint64_t offset, vm_page_t* page, bool zero,
bool do_range_update) {
canary_.Assert();
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
InitializeVmPage(page);
if (zero) {
ZeroPage(page);
}
VmPageOrMarker p = VmPageOrMarker::Page(page);
zx_status_t status = AddPageLocked(&p, offset, false);
if (status != ZX_OK) {
// Release the page from 'p', as we are returning failure 'page' is still owned by the caller.
p.ReleasePage();
}
return status;
}
zx_status_t VmCowPages::AddNewPagesLocked(uint64_t start_offset, list_node_t* pages, bool zero,
bool do_range_update) {
canary_.Assert();
DEBUG_ASSERT(IS_PAGE_ALIGNED(start_offset));
uint64_t offset = start_offset;
while (vm_page_t* p = list_remove_head_type(pages, vm_page_t, queue_node)) {
// Defer the range change update by passing false as we will do it in bulk at the end if needed.
zx_status_t status = AddNewPageLocked(offset, p, zero, false);
if (status != ZX_OK) {
// Put the page back on the list so that someone owns it and it'll get free'd.
list_add_head(pages, &p->queue_node);
// Decommit any pages we already placed.
if (offset > start_offset) {
DecommitRangeLocked(start_offset, offset - start_offset);
}
// Free all the pages back as we had ownership of them.
pmm_free(pages);
return status;
}
offset += PAGE_SIZE;
}
if (do_range_update) {
// other mappings may have covered this offset into the vmo, so unmap those ranges
RangeChangeUpdateLocked(start_offset, offset - start_offset, RangeChangeOp::Unmap);
}
return ZX_OK;
}
bool VmCowPages::IsUniAccessibleLocked(vm_page_t* page, uint64_t offset) const {
DEBUG_ASSERT(page_list_.Lookup(offset)->Page() == page);
if (page->object.cow_right_split || page->object.cow_left_split) {
return true;
}
if (offset < left_child_locked().parent_offset_ + left_child_locked().parent_start_limit_ ||
offset >= left_child_locked().parent_offset_ + left_child_locked().parent_limit_) {
return true;
}
if (offset < right_child_locked().parent_offset_ + right_child_locked().parent_start_limit_ ||
offset >= right_child_locked().parent_offset_ + right_child_locked().parent_limit_) {
return true;
}
return false;
}
vm_page_t* VmCowPages::CloneCowPageLocked(uint64_t offset, list_node_t* alloc_list,
VmCowPages* page_owner, vm_page_t* page,
uint64_t owner_offset) {
DEBUG_ASSERT(page != vm_get_zero_page());
DEBUG_ASSERT(parent_);
// To avoid the need for rollback logic on allocation failure, we start the forking
// process from the root-most vmo and work our way towards the leaf vmo. This allows
// us to maintain the hidden vmo invariants through the whole operation, so that we
// can stop at any point.
//
// To set this up, walk from the leaf to |page_owner|, and keep track of the
// path via |stack_.dir_flag|.
VmCowPages* cur = this;
do {
AssertHeld(cur->lock_);
VmCowPages* next = cur->parent_.get();
// We can't make COW clones of physical vmos, so this can only happen if we
// somehow don't find |page_owner| in the ancestor chain.
DEBUG_ASSERT(next);
AssertHeld(next->lock_);
next->stack_.dir_flag = &next->left_child_locked() == cur ? StackDir::Left : StackDir::Right;
if (next->stack_.dir_flag == StackDir::Right) {
DEBUG_ASSERT(&next->right_child_locked() == cur);
}
cur = next;
} while (cur != page_owner);
uint64_t cur_offset = owner_offset;
// |target_page| is the page we're considering for migration. Cache it
// across loop iterations.
vm_page_t* target_page = page;
bool alloc_failure = false;
// As long as we're simply migrating |page|, there's no need to update any vmo mappings, since
// that means the other side of the clone tree has already covered |page| and the current side
// of the clone tree will still see |page|. As soon as we insert a new page, we'll need to
// update all mappings at or below that level.
bool skip_range_update = true;
do {
// |target_page| is always located at in |cur| at |cur_offset| at the start of the loop.
VmCowPages* target_page_owner = cur;
AssertHeld(target_page_owner->lock_);
uint64_t target_page_offset = cur_offset;
cur = cur->stack_.dir_flag == StackDir::Left ? &cur->left_child_locked()
: &cur->right_child_locked();
DEBUG_ASSERT(cur_offset >= cur->parent_offset_);
cur_offset -= cur->parent_offset_;
if (target_page_owner->IsUniAccessibleLocked(target_page, target_page_offset)) {
// If the page we're covering in the parent is uni-accessible, then we
// can directly move the page.
// Assert that we're not trying to split the page the same direction two times. Either
// some tracking state got corrupted or a page in the subtree we're trying to
// migrate to got improperly migrated/freed. If we did this migration, then the
// opposite subtree would lose access to this page.
DEBUG_ASSERT(!(target_page_owner->stack_.dir_flag == StackDir::Left &&
target_page->object.cow_left_split));
DEBUG_ASSERT(!(target_page_owner->stack_.dir_flag == StackDir::Right &&
target_page->object.cow_right_split));
target_page->object.cow_left_split = 0;
target_page->object.cow_right_split = 0;
VmPageOrMarker removed = target_page_owner->page_list_.RemovePage(target_page_offset);
vm_page* removed_page = removed.ReleasePage();
pmm_page_queues()->Remove(removed_page);
DEBUG_ASSERT(removed_page == target_page);
} else {
// Otherwise we need to fork the page.
vm_page_t* cover_page;
alloc_failure = !AllocateCopyPage(pmm_alloc_flags_, page->paddr(), alloc_list, &cover_page);
if (unlikely(alloc_failure)) {
// TODO: plumb through PageRequest once anonymous page source is implemented.
break;
}
// We're going to cover target_page with cover_page, so set appropriate split bit.
if (target_page_owner->stack_.dir_flag == StackDir::Left) {
target_page->object.cow_left_split = 1;
DEBUG_ASSERT(target_page->object.cow_right_split == 0);
} else {
target_page->object.cow_right_split = 1;
DEBUG_ASSERT(target_page->object.cow_left_split == 0);
}
target_page = cover_page;
skip_range_update = false;
}
// Skip the automatic range update so we can do it ourselves more efficiently.
VmPageOrMarker add_page = VmPageOrMarker::Page(target_page);
zx_status_t status = cur->AddPageLocked(&add_page, cur_offset, false);
DEBUG_ASSERT(status == ZX_OK);
if (!skip_range_update) {
if (cur != this) {
// In this case, cur is a hidden vmo and has no direct mappings. Also, its
// descendents along the page stack will be dealt with by subsequent iterations
// of this loop. That means that any mappings that need to be touched now are
// owned by the children on the opposite side of stack_.dir_flag.
VmCowPages& other = cur->stack_.dir_flag == StackDir::Left ? cur->right_child_locked()
: cur->left_child_locked();
AssertHeld(other.lock_);
RangeChangeList list;
other.RangeChangeUpdateFromParentLocked(cur_offset, PAGE_SIZE, &list);
RangeChangeUpdateListLocked(&list, RangeChangeOp::Unmap);
} else {
// In this case, cur is the last vmo being changed, so update its whole subtree.
DEBUG_ASSERT(offset == cur_offset);
RangeChangeUpdateLocked(offset, PAGE_SIZE, RangeChangeOp::Unmap);
}
}
} while (cur != this);
DEBUG_ASSERT(alloc_failure || cur_offset == offset);
if (unlikely(alloc_failure)) {
return nullptr;
} else {
return target_page;
}
}
zx_status_t VmCowPages::CloneCowPageAsZeroLocked(uint64_t offset, list_node_t* freed_list,
VmCowPages* page_owner, vm_page_t* page,
uint64_t owner_offset) {
DEBUG_ASSERT(parent_);
// Ensure we have a slot as we'll need it later.
VmPageOrMarker* slot = page_list_.LookupOrAllocate(offset);
if (!slot) {
return ZX_ERR_NO_MEMORY;
}
// We cannot be forking a page to here if there's already something.
DEBUG_ASSERT(slot->IsEmpty());
// Need to make sure the page is duplicated as far as our parent. Then we can pretend
// that we have forked it into us by setting the marker.
AssertHeld(parent_->lock_);
if (page_owner != parent_.get()) {
// Do not pass our freed_list here as this wants an alloc_list to allocate from.
page = parent_->CloneCowPageLocked(offset + parent_offset_, nullptr, page_owner, page,
owner_offset);
if (page == nullptr) {
return ZX_ERR_NO_MEMORY;
}
}
bool left = this == &(parent_->left_child_locked());
// Page is in our parent. Check if its uni accessible, if so we can free it.
if (parent_->IsUniAccessibleLocked(page, offset + parent_offset_)) {
// Make sure we didn't already merge the page in this direction.
DEBUG_ASSERT(!(left && page->object.cow_left_split));
DEBUG_ASSERT(!(!left && page->object.cow_right_split));
vm_page* removed = parent_->page_list_.RemovePage(offset + parent_offset_).ReleasePage();
DEBUG_ASSERT(removed == page);
pmm_page_queues()->Remove(removed);
DEBUG_ASSERT(!list_in_list(&removed->queue_node));
list_add_tail(freed_list, &removed->queue_node);
} else {
if (left) {
page->object.cow_left_split = 1;
} else {
page->object.cow_right_split = 1;
}
}
// Insert the zero marker.
*slot = VmPageOrMarker::Marker();
return ZX_OK;
}
VmPageOrMarker* VmCowPages::FindInitialPageContentLocked(uint64_t offset, VmCowPages** owner_out,
uint64_t* owner_offset_out) {
// Search up the clone chain for any committed pages. cur_offset is the offset
// into cur we care about. The loop terminates either when that offset contains
// a committed page or when that offset can't reach into the parent.
VmPageOrMarker* page = nullptr;
VmCowPages* cur = this;
AssertHeld(cur->lock_);
uint64_t cur_offset = offset;
while (cur_offset < cur->parent_limit_) {
VmCowPages* parent = cur->parent_.get();
// If there's no parent, then parent_limit_ is 0 and we'll never enter the loop
DEBUG_ASSERT(parent);
AssertHeld(parent->lock_ref());
uint64_t parent_offset;
bool overflowed = add_overflow(cur->parent_offset_, cur_offset, &parent_offset);
ASSERT(!overflowed);
if (parent_offset >= parent->size_) {
// The offset is off the end of the parent, so cur is the VmObjectPaged
// which will provide the page.
break;
}
cur = parent;
cur_offset = parent_offset;
VmPageOrMarker* p = cur->page_list_.Lookup(parent_offset);
if (p && !p->IsEmpty()) {
page = p;
break;
}
}
*owner_out = cur;
*owner_offset_out = cur_offset;
return page;
}
void VmCowPages::UpdateOnAccessLocked(vm_page_t* page, uint64_t offset) {
// The only kinds of pages where there is anything to update on an access is pager backed pages.
// To that end we first want to determine, with certainty, that the provided page is in fact in
// the pager backed queue.
if (page == vm_get_zero_page()) {
return;
}
// Check if we have a page_source_. If we don't have one then none of our pages can be pager
// backed, so we can abort.
if (!page_source_) {
return;
}
// We know there is a page source and so most of the pages will be in the pager backed queue, with
// the exception of any pages that are pinned, those will be in the wired queue and so we need to
// skip them.
if (page->object.pin_count != 0) {
return;
}
// These asserts are for sanity, the above checks should have caused us to abort if these aren't
// true.
DEBUG_ASSERT(page->object.get_object() == reinterpret_cast<void*>(this));
DEBUG_ASSERT(page->object.get_page_offset() == offset);
// Although the page is already in the pager backed queue, this move causes it be moved to the
// front of the first queue, representing it was recently accessed.
pmm_page_queues()->MoveToPagerBacked(page, this, offset);
}
// Looks up the page at the requested offset, faulting it in if requested and necessary. If
// this VMO has a parent and the requested page isn't found, the parent will be searched.
//
// |alloc_list|, if not NULL, is a list of allocated but unused vm_page_t that
// this function may allocate from. This function will need at most one entry,
// and will not fail if |alloc_list| is a non-empty list, faulting in was requested,
// and offset is in range.
zx_status_t VmCowPages::GetPageLocked(uint64_t offset, uint pf_flags, list_node* alloc_list,
PageRequest* page_request, vm_page_t** const page_out,
paddr_t* const pa_out) {
canary_.Assert();
DEBUG_ASSERT(!is_hidden_locked());
if (offset >= size_) {
return ZX_ERR_OUT_OF_RANGE;
}
offset = ROUNDDOWN(offset, PAGE_SIZE);
if (is_slice_locked()) {
uint64_t parent_offset;
VmCowPages* parent = PagedParentOfSliceLocked(&parent_offset);
AssertHeld(parent->lock_);
return parent->GetPageLocked(offset + parent_offset, pf_flags, alloc_list, page_request,
page_out, pa_out);
}
VmPageOrMarker* page_or_mark = page_list_.Lookup(offset);
vm_page* p = nullptr;
VmCowPages* page_owner;
uint64_t owner_offset;
if (page_or_mark && page_or_mark->IsPage()) {
// This is the common case where we have the page and don't need to do anything more, so
// return it straight away.
vm_page_t* p = page_or_mark->Page();
UpdateOnAccessLocked(p, offset);
if (page_out) {
*page_out = p;
}
if (pa_out) {
*pa_out = p->paddr();
}
return ZX_OK;
}
// Get content from parent if available, otherwise accept we are the owner of the yet to exist
// page.
if ((!page_or_mark || page_or_mark->IsEmpty()) && parent_) {
page_or_mark = FindInitialPageContentLocked(offset, &page_owner, &owner_offset);
} else {
page_owner = this;
owner_offset = offset;
}
// At this point we might not have an actual page, but we should at least have a notional owner.
DEBUG_ASSERT(page_owner);
__UNUSED char pf_string[5];
LTRACEF("vmo %p, offset %#" PRIx64 ", pf_flags %#x (%s)\n", this, offset, pf_flags,
vmm_pf_flags_to_string(pf_flags, pf_string));
// We need to turn this potential page or marker into a real vm_page_t. This means failing cases
// that we cannot handle, determining whether we can substitute the zero_page and potentially
// consulting a page_source.
if (page_or_mark && page_or_mark->IsPage()) {
p = page_or_mark->Page();
} else {
// If we don't have a real page and we're not sw or hw faulting in the page, return not found.
if ((pf_flags & VMM_PF_FLAG_FAULT_MASK) == 0) {
return ZX_ERR_NOT_FOUND;
}
// We need to get a real page as our initial content. At this point we are either starting from
// the zero page, or something supplied from a page source. The page source only fills in if we
// have a true absence of content.
if ((page_or_mark && page_or_mark->IsMarker()) || !page_owner->page_source_) {
// Either no relevant page source or this is a known marker, in which case the content is
// the zero page.
p = vm_get_zero_page();
} else {
AssertHeld(page_owner->lock_);
uint64_t user_id = 0;
if (page_owner->paged_ref_) {
AssertHeld(page_owner->paged_ref_->lock_ref());
user_id = page_owner->paged_ref_->user_id_locked();
}
VmoDebugInfo vmo_debug_info = {.vmo_ptr = reinterpret_cast<uintptr_t>(page_owner->paged_ref_),
.vmo_id = user_id};
zx_status_t status = page_owner->page_source_->GetPage(owner_offset, page_request,
vmo_debug_info, &p, nullptr);
// Pager page sources will never synchronously return a page.
DEBUG_ASSERT(status != ZX_OK);
return status;
}
}
// If we made it this far we must have some valid vm_page in |p|. Although this may be the zero
// page, the rest of this function is tolerant towards correctly forking it.
DEBUG_ASSERT(p);
// It's possible that we are going to fork the page, and the user isn't actually going to directly
// use `p`, but creating the fork still uses `p` so we want to consider it accessed.
AssertHeld(page_owner->lock_);
page_owner->UpdateOnAccessLocked(p, owner_offset);
if ((pf_flags & VMM_PF_FLAG_WRITE) == 0) {
// If we're read-only faulting, return the page so they can map or read from it directly.
if (page_out) {
*page_out = p;
}
if (pa_out) {
*pa_out = p->paddr();
}
LTRACEF("read only faulting in page %p, pa %#" PRIxPTR " from parent\n", p, p->paddr());
return ZX_OK;
}
vm_page_t* res_page;
if (!page_owner->is_hidden_locked() || p == vm_get_zero_page()) {
// If the vmo isn't hidden, we can't move the page. If the page is the zero
// page, there's no need to try to move the page. In either case, we need to
// allocate a writable page for this vmo.
if (!AllocateCopyPage(pmm_alloc_flags_, p->paddr(), alloc_list, &res_page)) {
return ZX_ERR_NO_MEMORY;
}
VmPageOrMarker insert = VmPageOrMarker::Page(res_page);
zx_status_t status = AddPageLocked(&insert, offset);
if (status != ZX_OK) {
// AddPageLocked failing for any other reason is a programming error.
DEBUG_ASSERT_MSG(status == ZX_ERR_NO_MEMORY, "status=%d\n", status);
pmm_free_page(insert.ReleasePage());
return status;
}
// Interpret a software fault as an explicit desire to have potential zero pages and don't
// consider them for cleaning, this is an optimization.
// We explicitly must *not* place pages from a page_source_ into the zero scanning queue.
if (p == vm_get_zero_page() && !page_source_ && !(pf_flags & VMM_PF_FLAG_SW_FAULT)) {
pmm_page_queues()->MoveToUnswappableZeroFork(res_page, this, offset);
}
// This is the only path where we can allocate a new page without being a clone (clones are
// always cached). So we check here if we are not fully cached and if so perform a
// clean/invalidate to flush our zeroes. After doing this we will not touch the page via the
// physmap and so we can pretend there isn't an aliased mapping.
// There are three potential states that may exist
// * VMO is cached, paged_ref_ might be null, we might have children -> no cache op needed
// * VMO is uncached, paged_ref_ is not null, we have no children -> cache op needed
// * VMO is uncached, paged_ref_ is null, we have no children -> cache op not needed /
// state cannot happen
// In the uncached case we know we have no children, since it is by definition not valid to
// have copy-on-write children of uncached pages. The third case cannot happen, but even if it
// could with no children and no paged_ref_ the pages cannot actually be referenced so any
// cache operation is pointless.
if (paged_ref_) {
AssertHeld(paged_ref_->lock_ref());
if (paged_ref_->GetMappingCachePolicyLocked() != ARCH_MMU_FLAG_CACHED) {
arch_clean_invalidate_cache_range((vaddr_t)paddr_to_physmap(res_page->paddr()), PAGE_SIZE);
}
}
} else {
// We need a writable page; let ::CloneCowPageLocked handle inserting one.
res_page = CloneCowPageLocked(offset, alloc_list, page_owner, p, owner_offset);
if (res_page == nullptr) {
return ZX_ERR_NO_MEMORY;
}
}
LTRACEF("faulted in page %p, pa %#" PRIxPTR "\n", res_page, res_page->paddr());
if (page_out) {
*page_out = res_page;
}
if (pa_out) {
*pa_out = res_page->paddr();
}
// If we made it here, we committed a new page in this VMO.
IncrementHierarchyGenerationCountLocked();
return ZX_OK;
}
zx_status_t VmCowPages::CommitRangeLocked(uint64_t offset, uint64_t len, uint64_t* committed_len,
PageRequest* page_request) {
canary_.Assert();
LTRACEF("offset %#" PRIx64 ", len %#" PRIx64 "\n", offset, len);
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(len));
DEBUG_ASSERT(InRange(offset, len, size_));
if (is_slice_locked()) {
uint64_t parent_offset;
VmCowPages* parent = PagedParentOfSliceLocked(&parent_offset);
AssertHeld(parent->lock_);
// PagedParentOfSliceLocked will walk all of the way up the VMO hierarchy
// until it hits a non-slice VMO. This guarantees that we should only ever
// recurse once instead of an unbound number of times. DEBUG_ASSERT this so
// that we don't actually end up with unbound recursion just in case the
// property changes.
DEBUG_ASSERT(!parent->is_slice_locked());
return parent->CommitRangeLocked(offset + parent_offset, len, committed_len, page_request);
}
fbl::RefPtr<PageSource> root_source = GetRootPageSourceLocked();
// If this vmo has a direct page source, then the source will provide the backing memory. For
// children that eventually depend on a page source, we skip preallocating memory to avoid
// potentially overallocating pages if something else touches the vmo while we're blocked on the
// request. Otherwise we optimize things by preallocating all the pages.
list_node page_list;
list_initialize(&page_list);
if (root_source == nullptr) {
// make a pass through the list to find out how many pages we need to allocate
size_t count = len / PAGE_SIZE;
page_list_.ForEveryPageInRange(
[&count](const auto* p, auto off) {
if (p->IsPage()) {
count--;
}
return ZX_ERR_NEXT;
},
offset, offset + len);
if (count == 0) {
*committed_len = len;
return ZX_OK;
}
zx_status_t status = pmm_alloc_pages(count, pmm_alloc_flags_, &page_list);
if (status != ZX_OK) {
return status;
}
}
auto list_cleanup = fbl::MakeAutoCall([&page_list]() {
if (!list_is_empty(&page_list)) {
pmm_free(&page_list);
}
});
const uint64_t start_offset = offset;
const uint64_t end = offset + len;
bool have_page_request = false;
while (offset < end) {
// Don't commit if we already have this page
VmPageOrMarker* p = page_list_.Lookup(offset);
if (!p || !p->IsPage()) {
// Check if our parent has the page
const uint flags = VMM_PF_FLAG_SW_FAULT | VMM_PF_FLAG_WRITE;
zx_status_t res = GetPageLocked(offset, flags, &page_list, page_request, nullptr, nullptr);
if (unlikely(res == ZX_ERR_SHOULD_WAIT)) {
// We can end up here in two cases:
// 1. We were in batch mode but had to terminate the batch early.
// 2. We hit the first missing page and we were not in batch mode.
//
// If we do have a page request, that means the batch was terminated early by pre-populated
// pages (case 1). Return immediately.
//
// Do not update the |committed_len| for case 1 as we are returning on encountering
// pre-populated pages while processing a batch. When that happens, we will terminate the
// batch we were processing and send out a page request for the contiguous range we've
// accumulated in the batch so far. And we will need to come back into this function again
// to reprocess the range the page request spanned, so we cannot claim any pages have been
// committed yet.
if (!have_page_request) {
// Not running in batch mode, and this is the first missing page (case 2). Update the
// committed length we have so far and return.
*committed_len = offset - start_offset;
}
return ZX_ERR_SHOULD_WAIT;
} else if (unlikely(res == ZX_ERR_NEXT)) {
// In batch mode, will need to finalize the request later.
if (!have_page_request) {
// Stash how much we have committed right now, as we are going to have to reprocess this
// range so we do not want to claim it was committed.
*committed_len = offset - start_offset;
have_page_request = true;
}
} else if (unlikely(res != ZX_OK)) {
return res;
}
}
offset += PAGE_SIZE;
}
if (have_page_request) {
// commited_len was set when have_page_request was set so can just return.
return root_source->FinalizeRequest(page_request);
}
// Processed the full range successfully
*committed_len = len;
return ZX_OK;
}
zx_status_t VmCowPages::PinRangeLocked(uint64_t offset, uint64_t len) {
canary_.Assert();
LTRACEF("offset %#" PRIx64 ", len %#" PRIx64 "\n", offset, len);
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(len));
DEBUG_ASSERT(InRange(offset, len, size_));
if (is_slice_locked()) {
uint64_t parent_offset;
VmCowPages* parent = PagedParentOfSliceLocked(&parent_offset);
AssertHeld(parent->lock_);
// PagedParentOfSliceLocked will walk all of the way up the VMO hierarchy
// until it hits a non-slice VMO. This guarantees that we should only ever
// recurse once instead of an unbound number of times. DEBUG_ASSERT this so
// that we don't actually end up with unbound recursion just in case the
// property changes.
DEBUG_ASSERT(!parent->is_slice_locked());
return parent->PinRangeLocked(offset + parent_offset, len);
}
// Tracks our expected page offset when iterating to ensure all pages are present.
uint64_t next_offset = offset;
// Should any errors occur we need to unpin everything.
auto pin_cleanup = fbl::MakeAutoCall([this, offset, &next_offset]() {
if (next_offset > offset) {
AssertHeld(*lock());
UnpinLocked(offset, next_offset - offset);
}
});
zx_status_t status = page_list_.ForEveryPageInRange(
[&next_offset](const VmPageOrMarker* p, uint64_t page_offset) {
if (page_offset != next_offset || !p->IsPage()) {
return ZX_ERR_BAD_STATE;
}
vm_page_t* page = p->Page();
DEBUG_ASSERT(page->state() == VM_PAGE_STATE_OBJECT);
if (page->object.pin_count == VM_PAGE_OBJECT_MAX_PIN_COUNT) {
return ZX_ERR_UNAVAILABLE;
}
page->object.pin_count++;
if (page->object.pin_count == 1) {
pmm_page_queues()->MoveToWired(page);
}
// Pinning every page in the largest vmo possible as many times as possible can't overflow
static_assert(VmPageList::MAX_SIZE / PAGE_SIZE < UINT64_MAX / VM_PAGE_OBJECT_MAX_PIN_COUNT);
next_offset += PAGE_SIZE;
return ZX_ERR_NEXT;
},
offset, offset + len);
const uint64_t actual = (next_offset - offset) / PAGE_SIZE;
// Count whatever pages we pinned, in the failure scenario this will get decremented on the unpin.
pinned_page_count_ += actual;
if (status == ZX_OK) {
// If the missing pages were at the end of the range (or the range was empty) then our iteration
// will have just returned ZX_OK. Perform one final check that we actually pinned the number of
// pages we expected to.
const uint64_t expected = len / PAGE_SIZE;
if (actual != expected) {
status = ZX_ERR_BAD_STATE;
} else {
pin_cleanup.cancel();
}
}
return status;
}
zx_status_t VmCowPages::DecommitRangeLocked(uint64_t offset, uint64_t len) {
canary_.Assert();
// Trim the size and perform our zero-length hot-path check before we recurse
// up to our top-level ancestor. Size bounding needs to take place relative
// to the child the operation was originally targeted against.
uint64_t new_len;
if (!TrimRange(offset, len, size_, &new_len)) {
return ZX_ERR_OUT_OF_RANGE;
}
// was in range, just zero length
if (new_len == 0) {
return ZX_OK;
}
// If this is a child slice of a VMO, then find our way up to our root
// ancestor (taking our offset into account as we do), and then recurse,
// running the operation against our ancestor. Note that
// PagedParentOfSliceLocked will iteratively walk all the way up to our
// non-slice ancestor, not just our immediate parent, so we can guaranteed
// bounded recursion.
if (is_slice_locked()) {
uint64_t parent_offset;
VmCowPages* parent = PagedParentOfSliceLocked(&parent_offset);
AssertHeld(parent->lock_);
DEBUG_ASSERT(!parent->is_slice_locked()); // assert bounded recursion.
return parent->DecommitRangeLocked(offset + parent_offset, new_len);
}
if (parent_ || GetRootPageSourceLocked()) {
return ZX_ERR_NOT_SUPPORTED;
}
// Demand offset and length be correctly aligned to not give surprising user semantics.
if (!IS_PAGE_ALIGNED(offset) || !IS_PAGE_ALIGNED(len)) {
return ZX_ERR_INVALID_ARGS;
}
return UnmapAndRemovePagesLocked(offset, new_len);
}
zx_status_t VmCowPages::UnmapAndRemovePagesLocked(uint64_t offset, uint64_t len) {
// TODO(teisenbe): Allow decommitting of pages pinned by
// CommitRangeContiguous
if (AnyPagesPinnedLocked(offset, len)) {
return ZX_ERR_BAD_STATE;
}
LTRACEF("start offset %#" PRIx64 ", end %#" PRIx64 "\n", offset, offset + len);
// We've already trimmed the range in DecommitRangeLocked().
DEBUG_ASSERT(InRange(offset, len, size_));
// Verify page alignment.
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(len) || (offset + len == size_));
// DecommitRangeLocked() will call this function only on a VMO with no parent. The only clone
// types that support OP_DECOMMIT are slices, for which we will recurse up to the root.
// The only other callsite, DetachSourceLocked(), can only be called on a root pager-backed VMO.
DEBUG_ASSERT(!parent_);
// unmap all of the pages in this range on all the mapping regions
RangeChangeUpdateLocked(offset, len, RangeChangeOp::Unmap);
list_node_t freed_list;
list_initialize(&freed_list);
BatchPQRemove page_remover(&freed_list);
page_list_.RemovePages(page_remover.RemovePagesCallback(), offset, offset + len);
page_remover.Flush();
pmm_free(&freed_list);
return ZX_OK;
}
bool VmCowPages::PageWouldReadZeroLocked(uint64_t page_offset) {
DEBUG_ASSERT(IS_PAGE_ALIGNED(page_offset));
DEBUG_ASSERT(page_offset < size_);
VmPageOrMarker* slot = page_list_.Lookup(page_offset);
if (slot && slot->IsMarker()) {
// This is already considered zero as there's a marker.
return true;
}
// If we don't have a committed page we need to check our parent.
if (!slot || !slot->IsPage()) {
VmCowPages* page_owner;
uint64_t owner_offset;
if (!FindInitialPageContentLocked(page_offset, &page_owner, &owner_offset)) {
// Parent doesn't have a page either, so would also read as zero, assuming no page source.
return GetRootPageSourceLocked() == nullptr;
}
}
// Content either locally or in our parent, assume it is non-zero and return false.
return false;
}
zx_status_t VmCowPages::ZeroPagesLocked(uint64_t page_start_base, uint64_t page_end_base) {
canary_.Assert();
DEBUG_ASSERT(page_start_base <= page_end_base);
DEBUG_ASSERT(page_end_base <= size_);
DEBUG_ASSERT(IS_PAGE_ALIGNED(page_start_base));
DEBUG_ASSERT(IS_PAGE_ALIGNED(page_end_base));
// Forward any operations on slices up to the original non slice parent.
if (is_slice_locked()) {
uint64_t parent_offset;
VmCowPages* parent = PagedParentOfSliceLocked(&parent_offset);
AssertHeld(parent->lock_);
return parent->ZeroPagesLocked(page_start_base + parent_offset, page_end_base + parent_offset);
}
// First try and do the more efficient decommit. We prefer/ decommit as it performs work in the
// order of the number of committed pages, instead of work in the order of size of the range. An
// error from DecommitRangeLocked indicates that the VMO is not of a form that decommit can safely
// be performed without exposing data that we shouldn't between children and parents, but no
// actual state will have been changed. Should decommit succeed we are done, otherwise we will
// have to handle each offset individually.
zx_status_t status = DecommitRangeLocked(page_start_base, page_end_base - page_start_base);
if (status == ZX_OK) {
return ZX_OK;
}
// Unmap any page that is touched by this range in any of our, or our childrens, mapping regions.
// We do this on the assumption we are going to be able to free pages either completely or by
// turning them into markers and it's more efficient to unmap once in bulk here.
RangeChangeUpdateLocked(page_start_base, page_end_base - page_start_base, RangeChangeOp::Unmap);
list_node_t freed_list;
list_initialize(&freed_list);
auto auto_free = fbl::MakeAutoCall([&freed_list]() {
if (!list_is_empty(&freed_list)) {
pmm_free(&freed_list);
}
});
// Give us easier names for our range.
uint64_t start = page_start_base;
uint64_t end = page_end_base;
// If we're zeroing at the end of our parent range we can update to reflect this similar to a
// resize. This does not work if we are a slice, but we checked for that earlier. Whilst this does
// not actually zero the range in question, it makes future zeroing of the range far more
// efficient, which is why we do it first.
// parent_limit_ is a page aligned offset and so we can only reduce it to a rounded up value of
// start.
uint64_t rounded_start = ROUNDUP_PAGE_SIZE(start);
if (rounded_start < parent_limit_ && end >= parent_limit_) {
bool hidden_parent = false;
if (parent_) {
AssertHeld(parent_->lock_ref());
hidden_parent = parent_->is_hidden_locked();
}
if (hidden_parent) {
// Release any COW pages that are no longer necessary. This will also
// update the parent limit.
BatchPQRemove page_remover(&freed_list);
ReleaseCowParentPagesLocked(rounded_start, parent_limit_, &page_remover);
page_remover.Flush();
} else {
parent_limit_ = rounded_start;
}
}
for (uint64_t offset = start; offset < end; offset += PAGE_SIZE) {
VmPageOrMarker* slot = page_list_.Lookup(offset);
const bool can_see_parent = parent_ && offset < parent_limit_;
// This is a lambda as it only makes sense to talk about parent mutability when we have a parent
// for this offset.
auto parent_immutable = [can_see_parent, this]() TA_REQ(lock_) {
DEBUG_ASSERT(can_see_parent);
AssertHeld(parent_->lock_ref());
return parent_->is_hidden_locked();
};
// Finding the initial page content is expensive, but we only need to call it
// under certain circumstances scattered in the code below. The lambda
// get_initial_page_content() will lazily fetch and cache the details. This
// avoids us calling it when we don't need to, or calling it more than once.
struct InitialPageContent {
bool inited = false;
VmCowPages* page_owner;
uint64_t owner_offset;
vm_page_t* page;
} initial_content_;
auto get_initial_page_content = [&initial_content_, can_see_parent, this, offset]()
TA_REQ(lock_) -> const InitialPageContent& {
if (!initial_content_.inited) {
DEBUG_ASSERT(can_see_parent);
VmPageOrMarker* page_or_marker = FindInitialPageContentLocked(
offset, &initial_content_.page_owner, &initial_content_.owner_offset);
// We only care about the parent having a 'true' vm_page for content. If the parent has a
// marker then it's as if the parent has no content since that's a zero page anyway, which
// is what we are trying to achieve.
initial_content_.page =
page_or_marker && page_or_marker->IsPage() ? page_or_marker->Page() : nullptr;
initial_content_.inited = true;
}
return initial_content_;
};
auto parent_has_content = [get_initial_page_content]() TA_REQ(lock_) {
return get_initial_page_content().page != nullptr;
};
// Ideally we just collect up pages and hand them over to the pmm all at the end, but if we need
// to allocate any pages then we would like to ensure that we do not cause total memory to peak
// higher due to squirreling these pages away.
auto free_any_pages = [&freed_list] {
if (!list_is_empty(&freed_list)) {
pmm_free(&freed_list);
}
};
// If there's already a marker then we can avoid any second guessing and leave the marker alone.
if (slot && slot->IsMarker()) {
continue;
}
// In the ideal case we can zero by making there be an Empty slot in our page list, so first
// see if we can do that. This is true when there is nothing pinned and either:
// * This offset does not relate to our parent
// * This offset does relate to our parent, but our parent is immutable and is currently zero
// at this offset.
if (!SlotHasPinnedPage(slot) &&
(!can_see_parent || (parent_immutable() && !parent_has_content()))) {
if (slot && slot->IsPage()) {
vm_page_t* page = page_list_.RemovePage(offset).ReleasePage();
pmm_page_queues()->Remove(page);
DEBUG_ASSERT(!list_in_list(&page->queue_node));
list_add_tail(&freed_list, &page->queue_node);
}
continue;
}
// The only time we would reach either and *not* have a parent is if the page is pinned
DEBUG_ASSERT(SlotHasPinnedPage(slot) || parent_);
// Now we know that we need to do something active to make this zero, either through a marker or
// a page. First make sure we have a slot to modify.
if (!slot) {
slot = page_list_.LookupOrAllocate(offset);
if (unlikely(!slot)) {
return ZX_ERR_NO_MEMORY;
}
}
// Ideally we will use a marker, but we can only do this if we can point to a committed page
// to justify the allocation of the marker (i.e. we cannot allocate infinite markers with no
// committed pages). A committed page in this case exists if the parent has any content.
if (SlotHasPinnedPage(slot) || !parent_has_content()) {
if (slot->IsPage()) {
// Zero the existing page.
ZeroPage(slot->Page());
continue;
}
// Allocate a new page, it will be zeroed in the process.
vm_page_t* p;
free_any_pages();
// Do not pass our freed_list here as this takes an |alloc_list| list to allocate from.
bool result = AllocateCopyPage(pmm_alloc_flags_, vm_get_zero_page_paddr(), nullptr, &p);
if (!result) {
return ZX_ERR_NO_MEMORY;
}
SetNotWired(p, offset);
*slot = VmPageOrMarker::Page(p);
continue;
}
DEBUG_ASSERT(parent_ && parent_has_content());
// We are able to insert a marker, but if our page content is from a hidden owner we need to
// perform slightly more complex cow forking.
const InitialPageContent& content = get_initial_page_content();
AssertHeld(content.page_owner->lock_ref());
if (slot->IsEmpty() && content.page_owner->is_hidden_locked()) {
free_any_pages();
zx_status_t result = CloneCowPageAsZeroLocked(offset, &freed_list, content.page_owner,
content.page, content.owner_offset);
if (result != ZX_OK) {
return result;
}
continue;
}
// Remove any page that could be hanging around in the slot before we make it a marker.
if (slot->IsPage()) {
vm_page_t* page = slot->ReleasePage();
DEBUG_ASSERT(page->object.pin_count == 0);
pmm_page_queues()->Remove(page);
DEBUG_ASSERT(!list_in_list(&page->queue_node));
list_add_tail(&freed_list, &page->queue_node);
}
*slot = VmPageOrMarker::Marker();
}
return ZX_OK;
}
void VmCowPages::MoveToNotWired(vm_page_t* page, uint64_t offset) {
if (page_source_) {
pmm_page_queues()->MoveToPagerBacked(page, this, offset);
} else {
pmm_page_queues()->MoveToUnswappable(page);
}
}
void VmCowPages::SetNotWired(vm_page_t* page, uint64_t offset) {
if (page_source_) {
pmm_page_queues()->SetPagerBacked(page, this, offset);
} else {
pmm_page_queues()->SetUnswappable(page);
}
}
void VmCowPages::UnpinPage(vm_page_t* page, uint64_t offset) {
DEBUG_ASSERT(page->state() == VM_PAGE_STATE_OBJECT);
ASSERT(page->object.pin_count > 0);
page->object.pin_count--;
if (page->object.pin_count == 0) {
MoveToNotWired(page, offset);
}
}
void VmCowPages::PromoteRangeForReclamationLocked(uint64_t offset, uint64_t len) {
canary_.Assert();
// We will have pages only if we are directly backed by a pager source.
if (!page_source_) {
return;
}
const uint64_t start_offset = ROUNDDOWN(offset, PAGE_SIZE);
const uint64_t end_offset = ROUNDUP(offset + len, PAGE_SIZE);
page_list_.ForEveryPageInRange(
[](const auto* p, uint64_t) {
if (p->IsPage()) {
pmm_page_queues()->MoveToEndOfPagerBacked(p->Page());
}
return ZX_ERR_NEXT;
},
start_offset, end_offset);
}
void VmCowPages::UnpinLocked(uint64_t offset, uint64_t len) {
canary_.Assert();
// verify that the range is within the object
ASSERT(InRange(offset, len, size_));
// forbid zero length unpins as zero length pins return errors.
ASSERT(len != 0);
if (is_slice_locked()) {
uint64_t parent_offset;
VmCowPages* parent = PagedParentOfSliceLocked(&parent_offset);
AssertHeld(parent->lock_);
return parent->UnpinLocked(offset + parent_offset, len);
}
const uint64_t start_page_offset = ROUNDDOWN(offset, PAGE_SIZE);
const uint64_t end_page_offset = ROUNDUP(offset + len, PAGE_SIZE);
zx_status_t status = page_list_.ForEveryPageAndGapInRange(
[this](const auto* page, uint64_t off) {
if (page->IsMarker()) {
return ZX_ERR_NOT_FOUND;
}
AssertHeld(lock_);
UnpinPage(page->Page(), off);
return ZX_ERR_NEXT;
},
[](uint64_t gap_start, uint64_t gap_end) { return ZX_ERR_NOT_FOUND; }, start_page_offset,
end_page_offset);
ASSERT_MSG(status == ZX_OK, "Tried to unpin an uncommitted page");
bool overflow = sub_overflow(
pinned_page_count_, (end_page_offset - start_page_offset) / PAGE_SIZE, &pinned_page_count_);
ASSERT(!overflow);
return;
}
bool VmCowPages::AnyPagesPinnedLocked(uint64_t offset, size_t len) {
canary_.Assert();
DEBUG_ASSERT(lock_.lock().IsHeld());
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(len));
const uint64_t start_page_offset = offset;
const uint64_t end_page_offset = offset + len;
if (pinned_page_count_ == 0) {
return false;
}
bool found_pinned = false;
page_list_.ForEveryPageInRange(
[&found_pinned, start_page_offset, end_page_offset](const auto* p, uint64_t off) {
DEBUG_ASSERT(off >= start_page_offset && off < end_page_offset);
if (p->IsPage() && p->Page()->object.pin_count > 0) {
found_pinned = true;
return ZX_ERR_STOP;
}
return ZX_ERR_NEXT;
},
start_page_offset, end_page_offset);
return found_pinned;
}
// Helper function which processes the region visible by both children.
void VmCowPages::ReleaseCowParentPagesLockedHelper(uint64_t start, uint64_t end,
bool sibling_visible,
BatchPQRemove* page_remover) {
// Compute the range in the parent that cur no longer will be able to see.
const uint64_t parent_range_start = CheckedAdd(start, parent_offset_);
const uint64_t parent_range_end = CheckedAdd(end, parent_offset_);
bool skip_split_bits = true;
if (parent_limit_ <= end) {
parent_limit_ = ktl::min(start, parent_limit_);
if (parent_limit_ <= parent_start_limit_) {
// Setting both to zero is cleaner and makes some asserts easier.
parent_start_limit_ = 0;
parent_limit_ = 0;
}
} else if (start == parent_start_limit_) {
parent_start_limit_ = end;
} else if (sibling_visible) {
// Split bits and partial cow release are only an issue if this range is also visible to our
// sibling. If it's not visible then we will always be freeing all pages anyway, no need to
// worry about split bits. Otherwise if the vmo limits can't be updated, this function will need
// to use the split bits to release pages in the parent. It also means that ancestor pages in
// the specified range might end up being released based on their current split bits, instead of
// through subsequent calls to this function. Therefore parent and all ancestors need to have
// the partial_cow_release_ flag set to prevent fast merge issues in ::RemoveChildLocked.
auto cur = this;
AssertHeld(cur->lock_);
uint64_t cur_start = start;
uint64_t cur_end = end;
while (cur->parent_ && cur_start < cur_end) {
auto parent = cur->parent_.get();
AssertHeld(parent->lock_);
parent->partial_cow_release_ = true;
cur_start = ktl::max(CheckedAdd(cur_start, cur->parent_offset_), parent->parent_start_limit_);
cur_end = ktl::min(CheckedAdd(cur_end, cur->parent_offset_), parent->parent_limit_);
cur = parent;
}
skip_split_bits = false;
}
// Free any pages that either aren't visible, or were already split into the other child. For
// pages that haven't been split into the other child, we need to ensure they're univisible.
AssertHeld(parent_->lock_);
parent_->page_list_.RemovePages(
[skip_split_bits, sibling_visible, page_remover,
left = this == &parent_->left_child_locked()](VmPageOrMarker* page_or_mark,
uint64_t offset) {
if (page_or_mark->IsMarker()) {
// If this marker is in a range still visible to the sibling then we just leave it, no
// split bits or anything to be updated. If the sibling cannot see it, then we can clear
// it.
if (!sibling_visible) {
*page_or_mark = VmPageOrMarker::Empty();
}
return ZX_ERR_NEXT;
}
vm_page* page = page_or_mark->Page();
// If the sibling can still see this page then we need to keep it around, otherwise we can
// free it. The sibling can see the page if this range is |sibling_visible| and if the
// sibling hasn't already forked the page, which is recorded in the split bits.
if (!sibling_visible || left ? page->object.cow_right_split : page->object.cow_left_split) {
page = page_or_mark->ReleasePage();
page_remover->Push(page);
return ZX_ERR_NEXT;
}
if (skip_split_bits) {
// If we were able to update this vmo's parent limit, that made the pages
// uniaccessible. We clear the split bits to allow ::RemoveChildLocked to efficiently
// merge vmos without having to worry about pages above parent_limit_.
page->object.cow_left_split = 0;
page->object.cow_right_split = 0;
} else {
// Otherwise set the appropriate split bit to make the page uniaccessible.
if (left) {
page->object.cow_left_split = 1;
} else {
page->object.cow_right_split = 1;
}
}
return ZX_ERR_NEXT;
},
parent_range_start, parent_range_end);
}
void VmCowPages::ReleaseCowParentPagesLocked(uint64_t start, uint64_t end,
BatchPQRemove* page_remover) {
// This function releases |this| references to any ancestor vmo's COW pages.
//
// To do so, we divide |this| parent into three (possibly 0-length) regions: the region
// which |this| sees but before what the sibling can see, the region where both |this|
// and its sibling can see, and the region |this| can see but after what the sibling can
// see. Processing the 2nd region only requires touching the direct parent, since the sibling
// can see ancestor pages in the region. However, processing the 1st and 3rd regions requires
// recursively releasing |this| parent's ancestor pages, since those pages are no longer
// visible through |this| parent.
//
// This function processes region 3 (incl. recursively processing the parent), then region 2,
// then region 1 (incl. recursively processing the parent). Processing is done in reverse order
// to ensure parent_limit_ is reduced correctly. When processing either regions of type 1 or 3 we
// 1. walk up the parent and find the largest common slice that all nodes in the hierarchy see
// as being of the same type.
// 2. walk back down (using stack_ direction flags) applying the range update using that final
// calculated size
// 3. reduce the range we are operating on to not include the section we just processed
// 4. repeat steps 1-3 until range is empty
// In the worst case it is possible for this algorithm then to be O(N^2) in the depth of the tree.
// More optimal algorithms probably exist, but this algorithm is sufficient for at the moment as
// these suboptimal scenarios do not occur in practice.
// At the top level we continuously attempt to process the range until it is empty.
while (end > start) {
// cur_start / cur_end get adjusted as cur moves up/down the parent chain.
uint64_t cur_start = start;
uint64_t cur_end = end;
VmCowPages* cur = this;
AssertHeld(cur->lock_);
// First walk up the parent chain as long as there is a visible parent that does not overlap
// with its sibling.
while (cur->parent_ && cur->parent_start_limit_ < cur_end && cur_start < cur->parent_limit_) {
if (cur_end > cur->parent_limit_) {
// Part of the range sees the parent, and part of it doesn't. As we only process ranges of
// a single type we first trim the range down to the portion that doesn't see the parent,
// then next time around the top level loop we will process the portion that does see
cur_start = cur->parent_limit_;
DEBUG_ASSERT(cur_start < cur_end);
break;
}
// Trim the start to the portion of the parent it can see.
cur_start = ktl::max(cur_start, cur->parent_start_limit_);
DEBUG_ASSERT(cur_start < cur_end);
// Work out what the overlap with our sibling is
auto parent = cur->parent_.get();
AssertHeld(parent->lock_);
bool left = cur == &parent->left_child_locked();
auto& other = left ? parent->right_child_locked() : parent->left_child_locked();
AssertHeld(other.lock_);
// Project our operating range into our parent.
const uint64_t our_parent_start = CheckedAdd(cur_start, cur->parent_offset_);
const uint64_t our_parent_end = CheckedAdd(cur_end, cur->parent_offset_);
// Project our siblings full range into our parent.
const uint64_t other_parent_start =
CheckedAdd(other.parent_offset_, other.parent_start_limit_);
const uint64_t other_parent_end = CheckedAdd(other.parent_offset_, other.parent_limit_);
if (other_parent_end >= our_parent_end && other_parent_start < our_parent_end) {
// At least some of the end of our range overlaps with the sibling. First move up our start
// to ensure our range is 100% overlapping.
if (other_parent_start > our_parent_start) {
cur_start = CheckedAdd(cur_start, other_parent_start - our_parent_start);
DEBUG_ASSERT(cur_start < cur_end);
}
// Free the range that overlaps with the sibling, then we are done walking up as this is the
// type 2 kind of region. It is safe to process this right now since we are in a terminal
// state and are leaving the loop, thus we know that this is the final size of the region.
cur->ReleaseCowParentPagesLockedHelper(cur_start, cur_end, true, page_remover);
break;
}
// End of our range does not see the sibling. First move up our start to ensure we are dealing
// with a range that is 100% no sibling, and then keep on walking up.
if (other_parent_end > our_parent_start && other_parent_end < our_parent_end) {
DEBUG_ASSERT(other_parent_end < our_parent_end);
cur_start = CheckedAdd(cur_start, other_parent_end - our_parent_start);
DEBUG_ASSERT(cur_start < cur_end);
}
// Record the direction so we can walk about down later.
parent->stack_.dir_flag = left ? StackDir::Left : StackDir::Right;
// Don't use our_parent_start as we may have updated cur_start
cur_start = CheckedAdd(cur_start, cur->parent_offset_);
cur_end = our_parent_end;
DEBUG_ASSERT(cur_start < cur_end);
cur = parent;
}
// Every parent that we walked up had no overlap with its siblings. Now that we know the size
// of the range that we can process we just walk back down processing.
while (cur != this) {
// Although we free pages in the parent we operate on the *child*, as that is whose limits
// we will actually adjust. The ReleaseCowParentPagesLockedHelper will then reach backup to
// the parent to actually free any pages.
cur = cur->stack_.dir_flag == StackDir::Left ? &cur->left_child_locked()
: &cur->right_child_locked();
AssertHeld(cur->lock_);
DEBUG_ASSERT(cur_start >= cur->parent_offset_);
DEBUG_ASSERT(cur_end >= cur->parent_offset_);
cur_start -= cur->parent_offset_;
cur_end -= cur->parent_offset_;
cur->ReleaseCowParentPagesLockedHelper(cur_start, cur_end, false, page_remover);
}
// Update the end with the portion we managed to do. Ensuring some basic sanity of the range,
// most importantly that we processed a non-zero portion to ensure progress.
DEBUG_ASSERT(cur_start >= start);
DEBUG_ASSERT(cur_start < end);
DEBUG_ASSERT(cur_end == end);
end = cur_start;
}
}
zx_status_t VmCowPages::ResizeLocked(uint64_t s) {
canary_.Assert();
LTRACEF("vmcp %p, size %" PRIu64 "\n", this, s);
// make sure everything is aligned before we get started
DEBUG_ASSERT(IS_PAGE_ALIGNED(size_));
DEBUG_ASSERT(IS_PAGE_ALIGNED(s));
DEBUG_ASSERT(!is_slice_locked());
list_node_t freed_list;
list_initialize(&freed_list);
BatchPQRemove page_remover(&freed_list);
// see if we're shrinking or expanding the vmo
if (s < size_) {
// shrinking
uint64_t start = s;
uint64_t end = size_;
uint64_t len = end - start;
// bail if there are any pinned pages in the range we're trimming
if (AnyPagesPinnedLocked(start, len)) {
return ZX_ERR_BAD_STATE;
}
// unmap all of the pages in this range on all the mapping regions
RangeChangeUpdateLocked(start, len, RangeChangeOp::Unmap);
if (page_source_) {
// Tell the page source that any non-resident pages that are now out-of-bounds
// were supplied, to ensure that any reads of those pages get woken up.
zx_status_t status = page_list_.ForEveryPageAndGapInRange(
[](const auto* p, uint64_t off) { return ZX_ERR_NEXT; },
[&](uint64_t gap_start, uint64_t gap_end) {
page_source_->OnPagesSupplied(gap_start, gap_end);
return ZX_ERR_NEXT;
},
start, end);
DEBUG_ASSERT(status == ZX_OK);
}
bool hidden_parent = false;
if (parent_) {
AssertHeld(parent_->lock_ref());
hidden_parent = parent_->is_hidden_locked();
}
if (hidden_parent) {
// Release any COW pages that are no longer necessary. This will also
// update the parent limit.
ReleaseCowParentPagesLocked(start, end, &page_remover);
// Validate that the parent limit was correctly updated as it should never remain larger than
// our actual size.
DEBUG_ASSERT(parent_limit_ <= s);
} else {
parent_limit_ = ktl::min(parent_limit_, s);
}
// If the tail of a parent disappears, the children shouldn't be able to see that region
// again, even if the parent is later reenlarged. So update the child parent limits.
UpdateChildParentLimitsLocked(s);
page_list_.RemovePages(page_remover.RemovePagesCallback(), start, end);
} else if (s > size_) {
uint64_t temp;
// Check that this VMOs new size would not cause it to overflow if projected onto the root.
bool overflow = add_overflow(root_parent_offset_, s, &temp);
if (overflow) {
return ZX_ERR_INVALID_ARGS;
}
// expanding
// figure the starting and ending page offset that is affected
uint64_t start = size_;
uint64_t end = s;
uint64_t len = end - start;
// inform all our children or mapping that there's new bits
RangeChangeUpdateLocked(start, len, RangeChangeOp::Unmap);
}
// save bytewise size
size_ = s;
page_remover.Flush();
pmm_free(&freed_list);
return ZX_OK;
}
void VmCowPages::UpdateChildParentLimitsLocked(uint64_t new_size) {
// Note that a child's parent_limit_ will limit that child's descendants' views into
// this vmo, so this method only needs to touch the direct children.
for (auto& child : children_list_) {
AssertHeld(child.lock_);
if (new_size < child.parent_offset_) {
child.parent_limit_ = 0;
} else {
child.parent_limit_ = ktl::min(child.parent_limit_, new_size - child.parent_offset_);
}
}
}
zx_status_t VmCowPages::LookupLocked(
uint64_t offset, uint64_t len,
fbl::Function<zx_status_t(uint64_t offset, paddr_t pa)> lookup_fn) {
canary_.Assert();
if (unlikely(len == 0)) {
return ZX_ERR_INVALID_ARGS;
}
// verify that the range is within the object
if (unlikely(!InRange(offset, len, size_))) {
return ZX_ERR_OUT_OF_RANGE;
}
if (is_slice_locked()) {
DEBUG_ASSERT(parent_);
AssertHeld(parent_->lock_ref());
// Slices are always hung off a non-slice parent, so we know we only need to walk up one level.
DEBUG_ASSERT(!parent_->is_slice_locked());
return parent_->LookupLocked(offset + parent_offset_, len, ktl::move(lookup_fn));
}
const uint64_t start_page_offset = ROUNDDOWN(offset, PAGE_SIZE);
const uint64_t end_page_offset = ROUNDUP(offset + len, PAGE_SIZE);
return page_list_.ForEveryPageInRange(
[&lookup_fn](const auto* p, uint64_t off) {
if (!p->IsPage()) {
// Skip non pages.
return ZX_ERR_NEXT;
}
paddr_t pa = p->Page()->paddr();
return lookup_fn(off, pa);
},
start_page_offset, end_page_offset);
}
zx_status_t VmCowPages::TakePagesLocked(uint64_t offset, uint64_t len, VmPageSpliceList* pages) {
canary_.Assert();
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(len));
if (!InRange(offset, len, size_)) {
return ZX_ERR_OUT_OF_RANGE;
}
if (AnyPagesPinnedLocked(offset, len) || parent_ || page_source_) {
return ZX_ERR_BAD_STATE;
}
// This is only used by the userpager API, which has significant restrictions on
// what sorts of vmos are acceptable. If splice starts being used in more places,
// then this restriction might need to be lifted.
// TODO: Check that the region is locked once locking is implemented
if (children_list_len_) {
return ZX_ERR_BAD_STATE;
}
page_list_.ForEveryPageInRange(
[](const auto* p, uint64_t off) {
if (p->IsPage()) {
DEBUG_ASSERT(p->Page()->object.pin_count == 0);
pmm_page_queues()->Remove(p->Page());
}
return ZX_ERR_NEXT;
},
offset, offset + len);
*pages = page_list_.TakePages(offset, len);
return ZX_OK;
}
zx_status_t VmCowPages::SupplyPagesLocked(uint64_t offset, uint64_t len, VmPageSpliceList* pages) {
canary_.Assert();
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(len));
ASSERT(page_source_);
if (!InRange(offset, len, size_)) {
return ZX_ERR_OUT_OF_RANGE;
}
uint64_t end = offset + len;
list_node freed_list;
list_initialize(&freed_list);
// [new_pages_start, new_pages_start + new_pages_len) tracks the current run of
// consecutive new pages added to this vmo.
uint64_t new_pages_start = offset;
uint64_t new_pages_len = 0;
zx_status_t status = ZX_OK;
while (!pages->IsDone()) {
VmPageOrMarker src_page = pages->Pop();
// The pager API does not allow the source VMO of supply pages to have a page source, so we can
// assume that any empty pages are zeroes and insert explicit markers here. We need to insert
// explicit markers to actually resolve the pager fault.
if (src_page.IsEmpty()) {
src_page = VmPageOrMarker::Marker();
}
// Defer individual range updates so we can do them in blocks.
status = AddPageLocked(&src_page, offset, /*do_range_update=*/false);
if (status == ZX_OK) {
new_pages_len += PAGE_SIZE;
} else {
if (src_page.IsPage()) {
vm_page_t* page = src_page.ReleasePage();
DEBUG_ASSERT(!list_in_list(&page->queue_node));
list_add_tail(&freed_list, &page->queue_node);
}
if (likely(status == ZX_ERR_ALREADY_EXISTS)) {
status = ZX_OK;
// We hit the end of a run of absent pages, so notify the pager source
// of any new pages that were added and reset the tracking variables.
if (new_pages_len) {
RangeChangeUpdateLocked(new_pages_start, new_pages_len, RangeChangeOp::Unmap);
page_source_->OnPagesSupplied(new_pages_start, new_pages_len);
}
new_pages_start = offset + PAGE_SIZE;
new_pages_len = 0;
} else {
break;
}
}
offset += PAGE_SIZE;
DEBUG_ASSERT(new_pages_start + new_pages_len <= end);
}
if (new_pages_len) {
RangeChangeUpdateLocked(new_pages_start, new_pages_len, RangeChangeOp::Unmap);
page_source_->OnPagesSupplied(new_pages_start, new_pages_len);
}
if (!list_is_empty(&freed_list)) {
pmm_free(&freed_list);
}
return status;
}
// This is a transient operation used only to fail currently outstanding page requests. It does not
// alter the state of the VMO, or any pages that might have already been populated within the
// specified range.
//
// If certain pages in this range are populated, we must have done so via a previous SupplyPages()
// call that succeeded. So it might be fine for clients to continue accessing them, despite the
// larger range having failed.
//
// TODO(rashaeqbal): If we support a more permanent failure mode in the future, we will need to free
// populated pages in the specified range, and possibly detach the VMO from the page source.
zx_status_t VmCowPages::FailPageRequestsLocked(uint64_t offset, uint64_t len,
zx_status_t error_status) {
canary_.Assert();
DEBUG_ASSERT(IS_PAGE_ALIGNED(offset));
DEBUG_ASSERT(IS_PAGE_ALIGNED(len));
// |error_status| must have already been validated by the PagerDispatcher.
DEBUG_ASSERT(PageSource::IsValidFailureCode(error_status));
ASSERT(page_source_);
if (!InRange(offset, len, size_)) {
return ZX_ERR_OUT_OF_RANGE;
}
page_source_->OnPagesFailed(offset, len, error_status);
return ZX_OK;
}
fbl::RefPtr<PageSource> VmCowPages::GetRootPageSourceLocked() const {
auto cow_pages = this;
AssertHeld(cow_pages->lock_);
while (cow_pages->parent_) {
cow_pages = cow_pages->parent_.get();
if (!cow_pages) {
return nullptr;
}
}
return cow_pages->page_source_;
}
void VmCowPages::DetachSourceLocked() {
DEBUG_ASSERT(page_source_);
page_source_->Detach();
// Remove committed pages so that all future page faults on this VMO and its clones can fail.
UnmapAndRemovePagesLocked(0, size_locked());
IncrementHierarchyGenerationCountLocked();
}
bool VmCowPages::IsCowClonableLocked() const {
// Copy-on-write clones of pager vmos or their descendants aren't supported as we can't
// efficiently make an immutable snapshot.
if (is_pager_backed_locked()) {
return false;
}
// Copy-on-write clones of slices aren't supported at the moment due to the resulting VMO chains
// having non hidden VMOs between hidden VMOs. This case cannot be handled be CloneCowPageLocked
// at the moment and so we forbid the construction of such cases for the moment.
// Bug: 36841
if (is_slice_locked()) {
return false;
}
return true;
}
VmCowPages* VmCowPages::PagedParentOfSliceLocked(uint64_t* offset) {
DEBUG_ASSERT(is_slice_locked());
DEBUG_ASSERT(parent_);
// Slices never have a slice parent, as there is no need to nest them.
AssertHeld(parent_->lock_ref());
DEBUG_ASSERT(!parent_->is_slice_locked());
*offset = parent_offset_;
return parent_.get();
}
void VmCowPages::RangeChangeUpdateFromParentLocked(const uint64_t offset, const uint64_t len,
RangeChangeList* list) {
canary_.Assert();
LTRACEF("offset %#" PRIx64 " len %#" PRIx64 " p_offset %#" PRIx64 " size_ %#" PRIx64 "\n", offset,
len, parent_offset_, size_);
// our parent is notifying that a range of theirs changed, see where it intersects
// with our offset into the parent and pass it on
uint64_t offset_new;
uint64_t len_new;
if (!GetIntersect(parent_offset_, size_, offset, len, &offset_new, &len_new)) {
return;
}
// if they intersect with us, then by definition the new offset must be >= parent_offset_
DEBUG_ASSERT(offset_new >= parent_offset_);
// subtract our offset
offset_new -= parent_offset_;
// verify that it's still within range of us
DEBUG_ASSERT(offset_new + len_new <= size_);
LTRACEF("new offset %#" PRIx64 " new len %#" PRIx64 "\n", offset_new, len_new);
// pass it on. to prevent unbounded recursion we package up our desired offset and len and add
// ourselves to the list. UpdateRangeLocked will then get called on it later.
// TODO: optimize by not passing on ranges that are completely covered by pages local to this vmo
range_change_offset_ = offset_new;
range_change_len_ = len_new;
list->push_front(this);
}
void VmCowPages::RangeChangeUpdateListLocked(RangeChangeList* list, RangeChangeOp op) {
while (!list->is_empty()) {
VmCowPages* object = list->pop_front();
AssertHeld(object->lock_);
// Check if there is an associated backlink, and if so pass the operation over.
if (object->paged_ref_) {
AssertHeld(object->paged_ref_->lock_ref());
object->paged_ref_->RangeChangeUpdateLocked(object->range_change_offset_,
object->range_change_len_, op);
}
// inform all our children this as well, so they can inform their mappings
for (auto& child : object->children_list_) {
AssertHeld(child.lock_);
child.RangeChangeUpdateFromParentLocked(object->range_change_offset_,
object->range_change_len_, list);
}
}
}
void VmCowPages::RangeChangeUpdateLocked(uint64_t offset, uint64_t len, RangeChangeOp op) {
canary_.Assert();
RangeChangeList list;
this->range_change_offset_ = offset;
this->range_change_len_ = len;
list.push_front(this);
RangeChangeUpdateListLocked(&list, op);
}
bool VmCowPages::EvictPage(vm_page_t* page, uint64_t offset) {
// Without a page source to bring the page back in we cannot even think about eviction.
if (!page_source_) {
return false;
}
Guard<Mutex> guard{&lock_};
// Check this page is still a part of this VMO.
VmPageOrMarker* page_or_marker = page_list_.Lookup(offset);
if (!page_or_marker || !page_or_marker->IsPage() || page_or_marker->Page() != page) {
return false;
}
// Pinned pages could be in use by DMA so we cannot safely evict them.
if (page->object.pin_count != 0) {
return false;
}
// Remove any mappings to this page before we remove it.
RangeChangeUpdateLocked(offset, PAGE_SIZE, RangeChangeOp::Unmap);
// Use RemovePage over just writing to page_or_marker so that the page list has the opportunity
// to release any now empty intermediate nodes.
vm_page_t* p = page_list_.RemovePage(offset).ReleasePage();
DEBUG_ASSERT(p == page);
pmm_page_queues()->Remove(page);
eviction_event_count_++;
IncrementHierarchyGenerationCountLocked();
// |page| is now owned by the caller.
return true;
}
bool VmCowPages::DebugValidatePageSplitsLocked() const {
canary_.Assert();
if (!is_hidden_locked()) {
// Nothing to validate on a leaf vmo.
return true;
}
// Assume this is valid until we prove otherwise.
bool valid = true;
page_list_.ForEveryPage([this, &valid](const VmPageOrMarker* page, uint64_t offset) {
if (!page->IsPage()) {
return ZX_ERR_NEXT;
}
vm_page_t* p = page->Page();
AssertHeld(this->lock_);
// We found a page in the hidden VMO, if it has been forked in either direction then we
// expect that if we search down that path we will find that the forked page and that no
// descendant can 'see' back to this page.
const VmCowPages* expected = nullptr;
if (p->object.cow_left_split) {
expected = &left_child_locked();
} else if (p->object.