zircon/system/utest/core/pager-writeback/pager-writeback.cc

// Copyright 2021 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/fit/defer.h>
#include <lib/zx/bti.h>
#include <lib/zx/iommu.h>
#include <zircon/syscalls-next.h>
#include <zircon/syscalls.h>
#include <zircon/syscalls/iommu.h>

#include <zxtest/zxtest.h>

#include "test_thread.h"
#include "userpager.h"

__BEGIN_CDECLS
__WEAK extern zx_handle_t get_root_resource(void);
__END_CDECLS

namespace pager_tests {

// Convenience macro for tests that want to create VMOs both with and without the ZX_VMO_TRAP_DIRTY
// flag. |base_create_option| specifies the common create options to be used for both cases. The
// test body must use the local variable |create_option| to create VMOs.
#define TEST_WITH_AND_WITHOUT_TRAP_DIRTY(fn_name, base_create_option)                           \
  void fn_name(uint32_t create_option);                                                         \
  TEST(PagerWriteback, fn_name##TrapDirty) { fn_name(base_create_option | ZX_VMO_TRAP_DIRTY); } \
  TEST(PagerWriteback, fn_name##NoTrapDirty) { fn_name(base_create_option); }                   \
  void fn_name(uint32_t create_option)

// Tests that a VMO created with TRAP_DIRTY can be supplied, and generates VMO_DIRTY requests when
// written to.
VMO_VMAR_TEST(PagerWriteback, SimpleTrapDirty) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));

  TestThread t1([vmo, check_vmar]() -> bool { return check_buffer(vmo, 0, 1, check_vmar); });
  ASSERT_TRUE(t1.Start());
  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 0, 1, ZX_TIME_INFINITE));

  // Supply the page first and then attempt to write to it.
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));
  ASSERT_TRUE(t1.Wait());

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  TestThread t2([vmo, &expected]() -> bool {
    uint8_t data = 0x77;
    expected[0] = data;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());

  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));

  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  ASSERT_TRUE(t2.Wait());

  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), check_vmar));

  // Writes to a VMO created without TRAP_DIRTY go through without blocking.
  Vmo* vmo_no_trap;
  ASSERT_TRUE(pager.CreateVmo(1, &vmo_no_trap));
  ASSERT_TRUE(pager.SupplyPages(vmo_no_trap, 0, 1));
  uint8_t data = 0xcc;
  ASSERT_OK(vmo_no_trap->vmo().write(&data, 0, sizeof(data)));

  vmo_no_trap->GenerateBufferContents(expected.data(), 1, 0);
  expected[0] = data;
  ASSERT_TRUE(check_buffer_data(vmo_no_trap, 0, 1, expected.data(), check_vmar));

  // Verify that a non pager-backed vmo cannot be created with TRAP_DIRTY.
  zx_handle_t handle;
  ASSERT_EQ(ZX_ERR_INVALID_ARGS,
            zx_vmo_create(zx_system_get_page_size(), ZX_VMO_TRAP_DIRTY, &handle));
}

// Tests that OP_DIRTY dirties pages even without a write to the VMO.
TEST(PagerWriteback, OpDirtyNoWrite) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  // Create a VMO and supply a page.
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  // Dirty the page directly with the pager op.
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));

  // The page should now be dirty.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // VMO content is unchanged.
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // No page requests seen.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that writing to the VMO with zx_vmo_write generates DIRTY requests as expected.
TEST(PagerWriteback, DirtyRequestsOnVmoWrite) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 20;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);

  TestThread t([vmo, &expected]() -> bool {
    uint8_t data = 0x77;
    // write alternate pages {0, 2, 4, 6, 8}.
    for (uint64_t i = 0; i < kNumPages / 2; i += 2) {
      expected[i * zx_system_get_page_size()] = data;
      if (vmo->vmo().write(&data, i * zx_system_get_page_size(), sizeof(data)) != ZX_OK) {
        return false;
      }
    }
    // write consecutive runs of pages too.
    // pages written at this point are [0] [2,3,4] [6] [8].
    expected[3 * zx_system_get_page_size()] = data;
    if (vmo->vmo().write(&data, 3 * zx_system_get_page_size(), sizeof(data)) != ZX_OK) {
      return false;
    }
    uint8_t buf[5 * zx_system_get_page_size()];
    memset(buf, 0, 5 * zx_system_get_page_size());
    memset(&expected[11 * zx_system_get_page_size()], 0, 5 * zx_system_get_page_size());
    // pages written are [11, 16).
    return vmo->vmo().write(&buf, 11 * zx_system_get_page_size(), sizeof(buf)) == ZX_OK;
  });
  ASSERT_TRUE(t.Start());

  for (uint64_t i = 0; i < kNumPages / 2; i += 2) {
    ASSERT_TRUE(t.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, i, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, i, 1));
  }

  ASSERT_TRUE(t.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 3, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 3, 1));

  ASSERT_TRUE(t.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 11, 5, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 11, 5));

  ASSERT_TRUE(t.Wait());

  // Verify dirty ranges.
  zx_vmo_dirty_range_t ranges[] = {{0, 1, 0}, {2, 3, 0}, {6, 1, 0}, {8, 1, 0}, {11, 5, 0}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges, sizeof(ranges) / sizeof(zx_vmo_dirty_range_t)));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // No more requests.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that writing to the VMO through a VM mapping generates DIRTY requests as expected.
TEST(PagerWriteback, DirtyRequestsViaMapping) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 20;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);

  zx_vaddr_t ptr;
  TestThread t([vmo, &ptr, &expected]() -> bool {
    // Map the vmo.
    if (zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                   kNumPages * zx_system_get_page_size(), &ptr) != ZX_OK) {
      fprintf(stderr, "could not map vmo\n");
      return false;
    }

    uint8_t data = 0xcc;
    auto buf = reinterpret_cast<uint8_t*>(ptr);
    // write alternate pages {0, 2, 4, 6, 8}.
    for (uint64_t i = 0; i < kNumPages / 2; i += 2) {
      expected[i * zx_system_get_page_size()] = data;
      buf[i * zx_system_get_page_size()] = data;
    }
    // write consecutive runs of pages too.
    // pages written at this point are [0] [2,3,4] [6] [8].
    expected[3 * zx_system_get_page_size()] = data;
    buf[3 * zx_system_get_page_size()] = data;
    // pages written are [11, 16).
    for (uint64_t i = 11; i < 16; i++) {
      expected[i * zx_system_get_page_size()] = data;
      buf[i * zx_system_get_page_size()] = data;
    }
    return true;
  });

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, kNumPages * zx_system_get_page_size());
  });

  ASSERT_TRUE(t.Start());

  for (uint64_t i = 0; i < kNumPages / 2; i += 2) {
    ASSERT_TRUE(t.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, i, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, i, 1));
  }

  ASSERT_TRUE(t.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 3, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 3, 1));

  ASSERT_TRUE(t.WaitForBlocked());
  // We're touching pages one by one via the mapping, so we'll see page requests for individual
  // pages. Wait for the first page request and dirty the whole range.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 11, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 11, 5));

  ASSERT_TRUE(t.Wait());

  // Verify dirty ranges.
  zx_vmo_dirty_range_t ranges[] = {{0, 1, 0}, {2, 3, 0}, {6, 1, 0}, {8, 1, 0}, {11, 5, 0}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges, sizeof(ranges) / sizeof(zx_vmo_dirty_range_t)));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // No more requests.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that no DIRTY requests are generated on a read.
TEST(PagerWriteback, NoDirtyRequestsOnRead) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 3;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));

  zx_vaddr_t ptr;
  uint8_t tmp;
  TestThread t([vmo, &ptr, &tmp]() -> bool {
    // Map the vmo.
    if (zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                   kNumPages * zx_system_get_page_size(), &ptr) != ZX_OK) {
      fprintf(stderr, "could not map vmo\n");
      return false;
    }

    auto buf = reinterpret_cast<uint8_t*>(ptr);
    // Read pages.
    for (uint64_t i = 0; i < kNumPages; i++) {
      tmp = buf[i * zx_system_get_page_size()];
    }
    return true;
  });

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, kNumPages * zx_system_get_page_size());
  });

  ASSERT_TRUE(t.Start());

  ASSERT_TRUE(t.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  ASSERT_TRUE(t.Wait());

  // No dirty requests should be seen as none of the pages were dirtied.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));

  // Should be able to read from the VMO without faulting now.
  uint8_t buf[kNumPages * zx_system_get_page_size()];
  ASSERT_TRUE(vmo->vmo().read(buf, 0, kNumPages * zx_system_get_page_size()) == ZX_OK);

  // No dirty requests should be seen as none of the pages were dirtied.
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));

  // No remaining reads.
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  // No dirty pages.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // Verify contents.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));
}

// Tests that DIRTY requests are generated only on the first write.
TEST(PagerWriteback, DirtyRequestsRepeatedWrites) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  zx_vaddr_t ptr;
  TestThread t1([vmo, &ptr, &expected]() -> bool {
    // Map the vmo.
    if (zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                   zx_system_get_page_size(), &ptr) != ZX_OK) {
      fprintf(stderr, "could not map vmo\n");
      return false;
    }

    uint8_t data = 0xcc;
    expected[0] = data;
    *reinterpret_cast<uint8_t*>(ptr) = data;
    return true;
  });

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, zx_system_get_page_size());
  });

  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));

  ASSERT_TRUE(t1.Wait());

  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Write to the page again.
  TestThread t2([ptr, &expected]() -> bool {
    uint8_t data = 0xdd;
    expected[0] = data;
    *reinterpret_cast<uint8_t*>(ptr) = data;
    return true;
  });

  ASSERT_TRUE(t2.Start());

  // No more requests seen.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  ASSERT_TRUE(t2.Wait());

  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that DIRTY requests are generated on a write to a page that was previously read from.
TEST(PagerWriteback, DirtyRequestsOnWriteAfterRead) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  zx_vaddr_t ptr;
  uint8_t tmp;
  TestThread t1([vmo, &ptr, &tmp]() -> bool {
    // Map the vmo.
    if (zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                   zx_system_get_page_size(), &ptr) != ZX_OK) {
      fprintf(stderr, "could not map vmo\n");
      return false;
    }

    // Read from the page.
    tmp = *reinterpret_cast<uint8_t*>(ptr);
    return true;
  });

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, zx_system_get_page_size());
  });

  ASSERT_TRUE(t1.Start());

  // No read or dirty requests.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  ASSERT_TRUE(t1.Wait());

  // Now write to the page. This should trigger a dirty request.
  TestThread t2([ptr, &expected]() -> bool {
    uint8_t data = 0xdd;
    expected[0] = data;
    *reinterpret_cast<uint8_t*>(ptr) = data;
    return true;
  });

  ASSERT_TRUE(t2.Start());

  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));

  ASSERT_TRUE(t2.Wait());

  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // No more requests.
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that no DIRTY requests are generated for clones of pager-backed VMOs.
TEST(PagerWriteback, NoDirtyRequestsForClones) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 3;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);

  auto clone = vmo->Clone();
  ASSERT_NOT_NULL(clone);

  // Write to the clone.
  TestThread t1([&vmo = clone->vmo()]() -> bool {
    uint8_t data[kNumPages * zx_system_get_page_size()];
    memset(data, 0xc, kNumPages * zx_system_get_page_size());
    return vmo.write(data, 0, kNumPages * zx_system_get_page_size()) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  // Writing the pages in the clone should trigger faults in the parent. Wait to see the first one.
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  // No dirty requests.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));

  ASSERT_TRUE(t1.Wait());

  // No dirty pages.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  for (uint64_t i = 0; i < kNumPages; i++) {
    uint8_t expected[zx_system_get_page_size()];
    memset(expected, 0xc, zx_system_get_page_size());
    uint8_t data[zx_system_get_page_size()];
    ASSERT_OK(clone->vmo().read(data, i * zx_system_get_page_size(), zx_system_get_page_size()));
    ASSERT_EQ(0, memcmp(expected, data, zx_system_get_page_size()));
  }

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // Write to the parent now. This should trigger dirty requests.
  TestThread t2([&vmo = vmo->vmo()]() -> bool {
    uint8_t data[kNumPages * zx_system_get_page_size()];
    memset(data, 0xd, kNumPages * zx_system_get_page_size());
    return vmo.write(data, 0, kNumPages * zx_system_get_page_size()) == ZX_OK;
  });
  ASSERT_TRUE(t2.Start());

  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, kNumPages, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, kNumPages));

  ASSERT_TRUE(t2.Wait());

  // Should now see the pages dirty.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = kNumPages};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  memset(expected.data(), 0xd, kNumPages * zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // No remaining requests.
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that writes for overlapping ranges generate the expected DIRTY requests.
TEST(PagerWriteback, DirtyRequestsOverlap) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 20;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);

  TestThread t1([vmo]() -> bool {
    // write pages [4,9).
    uint8_t data[5 * zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    return vmo->vmo().write((void*)&data, 4 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());
  ASSERT_TRUE(t1.WaitForBlocked());

  TestThread t2([vmo, &expected]() -> bool {
    // write pages [2,9).
    uint8_t data[7 * zx_system_get_page_size()];
    memset(data, 0xbb, sizeof(data));
    memset(expected.data() + 2 * zx_system_get_page_size(), 0xbb, sizeof(data));
    return vmo->vmo().write((void*)&data, 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());

  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 4, 5, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 2, ZX_TIME_INFINITE));

  // Dirty the range [4,9).
  ASSERT_TRUE(pager.DirtyPages(vmo, 4, 5));
  ASSERT_TRUE(t1.Wait());

  // Dirty the range [2,4).
  ASSERT_TRUE(pager.DirtyPages(vmo, 2, 2));
  ASSERT_TRUE(t2.Wait());

  // Verify dirty ranges.
  std::vector<zx_vmo_dirty_range_t> ranges;
  ranges.push_back({.offset = 2, .length = 7});
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges.data(), ranges.size()));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  TestThread t3([vmo, &expected]() -> bool {
    // write pages [11,16).
    uint8_t data[5 * zx_system_get_page_size()];
    memset(data, 0xcc, sizeof(data));
    memset(expected.data() + 11 * zx_system_get_page_size(), 0xcc, sizeof(data));
    return vmo->vmo().write((void*)&data, 11 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t3.Start());
  ASSERT_TRUE(t3.WaitForBlocked());

  TestThread t4([vmo, &expected]() -> bool {
    // write pages [15,19).
    uint8_t data[4 * zx_system_get_page_size()];
    memset(data, 0xdd, sizeof(data));
    memset(expected.data() + 15 * zx_system_get_page_size(), 0xdd, sizeof(data));
    return vmo->vmo().write((void*)&data, 15 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t4.Start());
  ASSERT_TRUE(t4.WaitForBlocked());

  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 11, 5, ZX_TIME_INFINITE));
  // No remaining requests.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));

  // Dirty the range [11,16).
  ASSERT_TRUE(pager.DirtyPages(vmo, 11, 5));

  // This should terminate t3, and wake up t4 until it blocks again for the remaining range.
  ASSERT_TRUE(t3.Wait());
  ASSERT_TRUE(t4.WaitForBlocked());

  // Verify dirty ranges.
  ranges.push_back({.offset = 11, .length = 5});
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges.data(), ranges.size()));

  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 16, 3, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 16, 3));

  ASSERT_TRUE(t4.Wait());

  // Verify dirty ranges.
  ranges.back().length = 8;
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges.data(), ranges.size()));

  // The contents of page 15 can vary depending on which of t3 or t4 wrote to it last, as both were
  // blocked on a dirty request for it at the same time, so there's a race.
  bool outcome1 = check_buffer_data(vmo, 0, kNumPages, expected.data(), true);
  memset(expected.data() + 15 * zx_system_get_page_size(), 0xcc, zx_system_get_page_size());
  bool outcome2 = check_buffer_data(vmo, 0, kNumPages, expected.data(), true);
  ASSERT_TRUE(outcome1 || outcome2);

  // No remaining requests.
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
}

// Tests that DIRTY requests are generated as expected for a VMO that has random offsets in various
// page states: {Empty, Clean, Dirty}.
TEST(PagerWriteback, DirtyRequestsRandomOffsets) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 10;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));

  int page_state[kNumPages];  // 0 for empty, 1 for clean, and 2 for dirty
  for (uint64_t i = 0; i < kNumPages; i++) {
    page_state[i] = rand() % 3;
    if (page_state[i] == 0) {
      // Page not present. Skip ahead.
      continue;
    } else if (page_state[i] == 1) {
      // Page is present and clean.
      ASSERT_TRUE(pager.SupplyPages(vmo, i, 1));
    } else {
      // Page is present and dirty.
      ASSERT_TRUE(pager.SupplyPages(vmo, i, 1));
      ASSERT_TRUE(pager.DirtyPages(vmo, i, 1));
    }
  }

  // Now write to the entire range. We should see a combination of read and dirty requests.
  TestThread t([&vmo = vmo->vmo()]() -> bool {
    uint8_t data[kNumPages * zx_system_get_page_size()];
    return vmo.write(data, 0, kNumPages * zx_system_get_page_size()) == ZX_OK;
  });
  ASSERT_TRUE(t.Start());

  uint64_t clean_start = 0;
  uint64_t clean_len = 0;
  for (uint64_t i = 0; i < kNumPages; i++) {
    if (page_state[i] == 0) {
      // Page is not present.
      // This might break an in-progress clean run, resolve that first.
      if (clean_len > 0) {
        ASSERT_TRUE(t.WaitForBlocked());
        ASSERT_TRUE(pager.WaitForPageDirty(vmo, clean_start, clean_len, ZX_TIME_INFINITE));
        ASSERT_TRUE(pager.DirtyPages(vmo, clean_start, clean_len));
      }
      // Should see a read request for this page now.
      ASSERT_TRUE(t.WaitForBlocked());
      ASSERT_TRUE(pager.WaitForPageRead(vmo, i, 1, ZX_TIME_INFINITE));
      ASSERT_TRUE(pager.SupplyPages(vmo, i, 1));

      // After the supply, visit this page again, as it might get combined into a subsequent clean
      // run. Set the page's state to clean, and decrement i.
      page_state[i] = 1;
      i--;

      clean_start = i + 1;
      clean_len = 0;

    } else if (page_state[i] == 1) {
      // Page is present and clean. Accumulate into the clean run.
      clean_len++;

    } else {
      // Page is present and dirty.
      // This might break an in-progress clean run, resolve that first.
      if (clean_len > 0) {
        ASSERT_TRUE(t.WaitForBlocked());
        ASSERT_TRUE(pager.WaitForPageDirty(vmo, clean_start, clean_len, ZX_TIME_INFINITE));
        ASSERT_TRUE(pager.DirtyPages(vmo, clean_start, clean_len));
      }
      clean_start = i + 1;
      clean_len = 0;
    }
  }

  // Resolve the last clean run if any.
  if (clean_len > 0) {
    ASSERT_TRUE(t.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, clean_start, clean_len, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, clean_start, clean_len));
  }

  ASSERT_TRUE(t.Wait());

  // No remaining requests.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that ZX_PAGER_OP_FAIL can fail DIRTY page requests and propagate the failure up.
TEST(PagerWriteback, FailDirtyRequests) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 2;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);

  zx_vaddr_t ptr;
  TestThread t1([vmo, &ptr]() -> bool {
    // Map the vmo.
    if (zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                   zx_system_get_page_size(), &ptr) != ZX_OK) {
      fprintf(stderr, "could not map vmo\n");
      return false;
    }
    // Write page 0.
    auto buf = reinterpret_cast<uint8_t*>(ptr);
    buf[0] = 0xcc;
    return true;
  });

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, zx_system_get_page_size());
  });

  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.FailPages(vmo, 0, 1));

  ASSERT_TRUE(t1.WaitForCrash(ptr, ZX_ERR_IO));

  // No pages should be dirty.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  TestThread t2([vmo]() -> bool {
    uint8_t data = 0xdd;
    // Write page 1.
    return vmo->vmo().write(&data, zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });

  ASSERT_TRUE(t2.Start());

  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 1, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.FailPages(vmo, 1, 1));

  ASSERT_TRUE(t2.WaitForFailure());

  // No pages should be dirty.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));
}

// Tests that partially failed DIRTY requests allow the write to partially complete.
TEST(PagerWriteback, PartialFailDirtyRequests) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  constexpr uint64_t kNumPages = 5;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);

  // Attempt to write to all the pages so we can partially succeed the request.
  TestThread t1([vmo]() -> bool {
    uint8_t data[kNumPages * zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());

  // Should see a dirty request spanning all pages.
  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, kNumPages, ZX_TIME_INFINITE));

  // Succeed a portion of the request, and fail the remaining.
  constexpr uint64_t kNumSuccess = 3;
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, kNumSuccess));
  ASSERT_TRUE(pager.FailPages(vmo, kNumSuccess, kNumPages - kNumSuccess));

  // We partially succeeded the previous request, so when the write resumes after blocking, we
  // should see another one for the failed portion. Fail it again to indicate failure starting at
  // the start offset of the new request, which will stop further retry attempts.
  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, kNumSuccess, kNumPages - kNumSuccess, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.FailPages(vmo, kNumSuccess, kNumPages - kNumSuccess));

  // The overall write should fail.
  ASSERT_TRUE(t1.WaitForFailure());

  // Only the successful portion should be dirty.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = kNumSuccess, .options = 0};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // The portion that succeeded should have modified contents.
  memset(expected.data(), 0xaa, kNumSuccess * zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // Clean the modified pages.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 0, kNumSuccess));
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 0, kNumSuccess));
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // Try to write again and this time fail at the start of the request.
  TestThread t2([vmo]() -> bool {
    uint8_t data[kNumPages * zx_system_get_page_size()];
    memset(data, 0xbb, sizeof(data));
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t2.Start());

  // Should see a dirty request spanning all pages.
  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, kNumPages, ZX_TIME_INFINITE));

  // Fail at the start of the request. This should terminate the blocked thread.
  ASSERT_TRUE(pager.FailPages(vmo, 0, kNumSuccess));
  ASSERT_TRUE(t2.WaitForFailure());

  // No dirty pages and no changes in VMO contents.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));
}

// Tests that DIRTY requests are generated when offsets with zero page markers are written to.
TEST(PagerWriteback, DirtyRequestsForZeroPages) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  constexpr uint64_t kNumPages = 2;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));

  // Supply with empty source vmo so that the destination gets zero page markers.
  zx::vmo vmo_src;
  ASSERT_OK(zx::vmo::create(kNumPages * zx_system_get_page_size(), 0, &vmo_src));
  ASSERT_OK(
      pager.pager().supply_pages(vmo->vmo(), 0, kNumPages * zx_system_get_page_size(), vmo_src, 0));

  // Verify that the pager vmo has no committed pages, i.e. it only has markers.
  zx_info_vmo_t info;
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(0, info.committed_bytes);

  // No dirty pages yet.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);

  // Write to the first page with zx_vmo_write.
  TestThread t1([vmo, &expected]() -> bool {
    uint8_t data = 0xaa;
    expected[0] = data;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());
  ASSERT_TRUE(t1.WaitForBlocked());

  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));

  // Dirty the first page.
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  ASSERT_TRUE(t1.Wait());

  // Verify that the pager vmo has one committed page now.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(zx_system_get_page_size(), info.committed_bytes);

  // Verify that the page is dirty.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  zx_vaddr_t ptr;
  // Map the second page of the vmo.
  ASSERT_OK(zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(),
                                       zx_system_get_page_size(), zx_system_get_page_size(), &ptr));

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, zx_system_get_page_size());
  });

  // Write to the second page via the mapping.
  auto buf = reinterpret_cast<uint8_t*>(ptr);
  uint8_t data = 0xbb;
  TestThread t2([buf, data, &expected]() -> bool {
    *buf = data;
    expected[zx_system_get_page_size()] = data;
    return true;
  });

  ASSERT_TRUE(t2.Start());

  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 1, 1, ZX_TIME_INFINITE));

  // Dirty the second page.
  ASSERT_TRUE(pager.DirtyPages(vmo, 1, 1));
  ASSERT_TRUE(t2.Wait());

  // Verify that the pager vmo has both pages committed now.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(kNumPages * zx_system_get_page_size(), info.committed_bytes);

  // Verify that both the pages are now dirty.
  range = {.offset = 0, .length = 2};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));
}

// Tests that ZX_PAGER_OP_DIRTY works for a mix of zero and non-zero pages.
TEST(PagerWriteback, DirtyZeroAndNonZeroPages) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  constexpr uint64_t kNumPages = 10;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);

  // Empty source vmo to supply with zero pages.
  zx::vmo vmo_src;
  ASSERT_OK(zx::vmo::create(zx_system_get_page_size(), 0, &vmo_src));

  // For each page offset, supply either a zero or a non-zero page.
  uint64_t non_zero_count = 0;
  for (uint64_t i = 0; i < kNumPages; i++) {
    if (rand() % 2) {
      non_zero_count++;
      ASSERT_TRUE(pager.SupplyPages(vmo, i, 1));
      vmo->GenerateBufferContents(expected.data() + i * zx_system_get_page_size(), 1, i);
    } else {
      ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), i * zx_system_get_page_size(),
                                           zx_system_get_page_size(), vmo_src, 0));
    }
  }

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // Only non-zero pages should be committed.
  zx_info_vmo_t info;
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(non_zero_count * zx_system_get_page_size(), info.committed_bytes);

  // No dirty pages yet.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // Verify that we're able to dirty the entire range regardless of the type of page.
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, kNumPages));

  // All the pages should be committed and dirty now.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(kNumPages * zx_system_get_page_size(), info.committed_bytes);
  zx_vmo_dirty_range_t range = {.offset = 0, .length = kNumPages};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));
}

// Tests that ZX_PAGER_OP_FAIL can fail DIRTY page requests for zero pages.
TEST(PagerWriteback, FailDirtyRequestsForZeroPages) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));

  // Supply with empty source vmo so that the destination gets zero page markers.
  zx::vmo vmo_src;
  ASSERT_OK(zx::vmo::create(zx_system_get_page_size(), 0, &vmo_src));
  ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), 0, zx_system_get_page_size(), vmo_src, 0));

  // Verify that the pager vmo has no committed pages, i.e. it only has markers.
  zx_info_vmo_t info;
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(0, info.committed_bytes);

  // No dirty pages yet.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);

  // Attempt to write to the first page.
  TestThread t([vmo]() -> bool {
    uint8_t data = 0xaa;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t.Start());
  ASSERT_TRUE(t.WaitForBlocked());

  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));

  // Fail the dirty request.
  ASSERT_TRUE(pager.FailPages(vmo, 0, 1));

  // The thread should exit with failure.
  ASSERT_TRUE(t.WaitForFailure());

  // No committed pages still.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(0, info.committed_bytes);

  // No dirty pages too.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that DIRTY requests are generated for ranges including zero pages as expected.
TEST(PagerWriteback, DirtyRequestsForZeroRanges) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  constexpr uint64_t kNumPages = 10;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);

  // Empty source vmo to supply with zero pages.
  zx::vmo vmo_src;
  ASSERT_OK(zx::vmo::create(zx_system_get_page_size(), 0, &vmo_src));

  // Supply zero page markers for pages 0 and 1.
  ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), 0, zx_system_get_page_size(), vmo_src, 0));
  ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), zx_system_get_page_size(),
                                       zx_system_get_page_size(), vmo_src, 0));

  // Attempt to write to the range [0, 2).
  TestThread t1([vmo, &expected]() -> bool {
    std::vector<uint8_t> data(2 * zx_system_get_page_size(), 0xaa);
    memset(expected.data(), 0xaa, 2 * zx_system_get_page_size());
    return vmo->vmo().write(data.data(), 0, 2 * zx_system_get_page_size()) == ZX_OK;
  });

  ASSERT_TRUE(t1.Start());
  ASSERT_TRUE(t1.WaitForBlocked());

  // We should see a dirty request for the range [0, 2). Verifies that the range is extended to
  // include another marker.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 2, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 2));
  ASSERT_TRUE(t1.Wait());

  // Verify dirty pages.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 2};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 2, expected.data(), true));

  // Supply a zero marker for page 2 and a non-zero page for page 3.
  ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), 2 * zx_system_get_page_size(),
                                       zx_system_get_page_size(), vmo_src, 0));
  ASSERT_TRUE(pager.SupplyPages(vmo, 3, 1));

  // Attempt to write to the range [2, 4).
  TestThread t2([vmo, &expected]() -> bool {
    std::vector<uint8_t> data(2 * zx_system_get_page_size(), 0xbb);
    memset(expected.data() + 2 * zx_system_get_page_size(), 0xbb, 2 * zx_system_get_page_size());
    return vmo->vmo().write(data.data(), 2 * zx_system_get_page_size(),
                            2 * zx_system_get_page_size()) == ZX_OK;
  });

  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());

  // We should see a dirty request for the range [2, 4). Verifies that the range is extended to
  // include a non-zero clean page.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 2, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 2, 2));
  ASSERT_TRUE(t2.Wait());

  // Verify dirty pages.
  range = {.offset = 0, .length = 4};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 4, expected.data(), true));

  // For the rest of the pages, supply a mix of zero and non-zero pages, leaving a gap at the end.
  for (uint64_t i = 4; i < kNumPages - 1; i++) {
    if (rand() % 2) {
      ASSERT_TRUE(pager.SupplyPages(vmo, i, 1));
    } else {
      ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), i * zx_system_get_page_size(),
                                           zx_system_get_page_size(), vmo_src, 0));
    }
  }

  // Attempt to write to the range [4, 10).
  TestThread t3([vmo, &expected]() -> bool {
    size_t len = kNumPages - 4;
    std::vector<uint8_t> data(len * zx_system_get_page_size(), 0xcc);
    memset(expected.data() + 4 * zx_system_get_page_size(), 0xcc, len * zx_system_get_page_size());
    return vmo->vmo().write(data.data(), 4 * zx_system_get_page_size(),
                            len * zx_system_get_page_size()) == ZX_OK;
  });

  ASSERT_TRUE(t3.Start());
  ASSERT_TRUE(t3.WaitForBlocked());

  // We should see a dirty request for pages [4, 9). Verifies that zero and non-zero clean pages get
  // picked up in a single range, and that the range stops before a gap.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 4, 5, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 4, 5));
  ASSERT_TRUE(t3.WaitForBlocked());

  // We should now see a read request followed by a dirty request for the last gap.
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 9, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.SupplyPages(vmo, 9, 1));
  ASSERT_TRUE(t3.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 9, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 9, 1));
  ASSERT_TRUE(t3.Wait());

  // Verify dirty pages.
  range = {.offset = 0, .length = kNumPages};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));
}

// Tests that no DIRTY requests are generated on a commit.
TEST(PagerWriteback, NoDirtyRequestsOnCommit) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 5;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));
  // Supply some pages.
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 2));

  // Commit the vmo.
  TestThread t([vmo]() -> bool {
    return vmo->vmo().op_range(ZX_VMO_OP_COMMIT, 0, kNumPages * zx_system_get_page_size(), nullptr,
                               0) == ZX_OK;
  });
  ASSERT_TRUE(t.Start());

  ASSERT_TRUE(t.WaitForBlocked());
  // Should see a read request for the uncommitted portion.
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 2, kNumPages - 2, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.SupplyPages(vmo, 2, kNumPages - 2));

  // The thread should be able to exit now.
  ASSERT_TRUE(t.Wait());

  // No dirty requests should be seen as none of the pages were dirtied.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));

  // No remaining reads.
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  // No dirty pages.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
}

// Tests that no DIRTY requests are generated when a mapping is created with MAP_RANGE.
TEST(PagerWriteback, NoDirtyRequestsOnMapRange) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  constexpr uint64_t kNumPages = 3;
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(kNumPages, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, kNumPages));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), kNumPages, 0);

  zx_vaddr_t ptr;
  TestThread t1([vmo, &ptr]() -> bool {
    // Map the vmo, and populate mappings for all committed pages. We know the pages are
    // pre-committed so we should not block on reads. And we should not be generating any dirty
    // requests to block on either.
    return zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE | ZX_VM_MAP_RANGE, 0,
                                      vmo->vmo(), 0, kNumPages * zx_system_get_page_size(),
                                      &ptr) == ZX_OK;
  });
  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, kNumPages * zx_system_get_page_size());
  });

  ASSERT_TRUE(t1.Start());

  // No dirty requests should be seen as none of the pages were dirtied.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  // No reads either.
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  ASSERT_TRUE(t1.Wait());

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  uint8_t tmp;
  TestThread t2([&ptr, &tmp]() -> bool {
    // Read the mapped pages. This will not block.
    auto buf = reinterpret_cast<uint8_t*>(ptr);
    for (uint64_t i = 0; i < kNumPages; i++) {
      tmp = buf[i * zx_system_get_page_size()];
    }
    return true;
  });

  ASSERT_TRUE(t2.Start());

  // No dirty or read requests.
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  ASSERT_TRUE(t2.Wait());

  // No dirty pages.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  TestThread t3([&ptr, &expected]() -> bool {
    // Now try to write to the vmo. This should result in write faults and dirty requests.
    auto buf = reinterpret_cast<uint8_t*>(ptr);
    for (uint64_t i = 0; i < kNumPages; i++) {
      uint8_t data = 0xcc;
      buf[i * zx_system_get_page_size()] = data;
      expected[i * zx_system_get_page_size()] = data;
    }
    return true;
  });

  ASSERT_TRUE(t3.Start());

  // The thread will block on dirty requests for each page.
  for (uint64_t i = 0; i < kNumPages; i++) {
    ASSERT_TRUE(t3.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, i, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, i, 1));
  }

  // The thread should now exit.
  ASSERT_TRUE(t3.Wait());

  // All pages are dirty now.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = kNumPages};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // No more dirty or read requests.
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that no DIRTY requests are generated when previously dirty pages are mapped and written to.
TEST(PagerWriteback, NoDirtyRequestsMapExistingDirty) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  // Dirty the page.
  TestThread t1([vmo, &expected]() -> bool {
    uint8_t data = 0xcc;
    expected[0] = data;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });

  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));

  ASSERT_TRUE(t1.Wait());

  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Map the page and try writing to it.
  zx_vaddr_t ptr;
  TestThread t2([vmo, &ptr, &expected]() -> bool {
    // Map the vmo.
    if (zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                   zx_system_get_page_size(), &ptr) != ZX_OK) {
      fprintf(stderr, "could not map vmo\n");
      return false;
    }

    uint8_t data = 0xdd;
    *reinterpret_cast<uint8_t*>(ptr) = data;
    expected[0] = data;
    return true;
  });

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, zx_system_get_page_size());
  });

  ASSERT_TRUE(t2.Start());

  // No read or dirty requests.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  ASSERT_TRUE(t2.Wait());

  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that dirty ranges cannot be queried on a clone.
TEST_WITH_AND_WITHOUT_TRAP_DIRTY(NoQueryOnClone, 0) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, create_option, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  uint8_t data = 0xaa;
  TestThread t([vmo, data]() -> bool { return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK; });
  ASSERT_TRUE(t.Start());

  if (create_option & ZX_VMO_TRAP_DIRTY) {
    ASSERT_TRUE(t.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  }
  ASSERT_TRUE(t.Wait());

  // Create a clone.
  auto clone = vmo->Clone();
  ASSERT_NOT_NULL(clone);

  // Write to the clone.
  uint8_t data_clone = 0x77;
  ASSERT_OK(clone->vmo().write(&data_clone, 0, sizeof(data_clone)));

  // Can query dirty ranges on the parent.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Verify parent contents.
  memset(expected.data(), data, sizeof(data));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Cannot query dirty ranges on the clone.
  uint64_t num_ranges = 0;
  ASSERT_EQ(ZX_ERR_INVALID_ARGS,
            zx_pager_query_dirty_ranges(pager.pager().get(), clone->vmo().get(), 0,
                                        zx_system_get_page_size(), &range, sizeof(range),
                                        &num_ranges, nullptr));

  // Verify clone contents.
  memset(expected.data(), data_clone, sizeof(data));
  ASSERT_TRUE(check_buffer_data(clone.get(), 0, 1, expected.data(), true));
}

// Tests that WRITEBACK_BEGIN/END clean pages as expected.
TEST_WITH_AND_WITHOUT_TRAP_DIRTY(SimpleWriteback, 0) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, create_option, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  // Dirty the page by writing to it.
  uint8_t data = 0xaa;
  TestThread t1(
      [vmo, data]() -> bool { return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK; });
  ASSERT_TRUE(t1.Start());

  if (create_option & ZX_VMO_TRAP_DIRTY) {
    ASSERT_TRUE(t1.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  }
  ASSERT_TRUE(t1.Wait());

  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  memset(expected.data(), data, sizeof(data));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Begin writeback on the page.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 0, 1));

  // The page is still dirty.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // This should transition the page to clean, and a subsequent write should trigger
  // another dirty request.
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 0, 1));

  // No dirty pages after writeback end.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Dirty the page again.
  TestThread t2([vmo, &expected]() -> bool {
    uint8_t data = 0x77;
    expected[0] = data;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });

  ASSERT_TRUE(t2.Start());

  if (create_option & ZX_VMO_TRAP_DIRTY) {
    // We should see a dirty request now.
    ASSERT_TRUE(t2.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  }
  ASSERT_TRUE(t2.Wait());

  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that a write after WRITEBACK_BEGIN but before WRITEBACK_END is handled correctly.
TEST(PagerWriteback, DirtyDuringWriteback) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  // Dirty the page.
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));

  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Begin writeback on the page.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 0, 1));

  // The page is still dirty.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Write to the page before ending writeback. This should generate a dirty request.
  TestThread t1([vmo, &expected]() -> bool {
    uint8_t data = 0xcc;
    expected[0] = data;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });

  ASSERT_TRUE(t1.Start());

  // Verify that we saw the dirty request but do not acknowledge it yet. The write will remain
  // blocked.
  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));

  // End the writeback. This should transition the page to clean.
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 0, 1));
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // The writing thread is still blocked.
  ASSERT_TRUE(t1.WaitForBlocked());

  // Now dirty the page, unblocking the writing thread.
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  ASSERT_TRUE(t1.Wait());

  // The page is dirty again.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Begin another writeback, and try writing again before ending it. This time acknowledge the
  // dirty request while the writeback is in progress.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 0, 1));
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Write to the page before ending writeback. This should generate a dirty request.
  TestThread t2([vmo, &expected]() -> bool {
    uint8_t data = 0xdd;
    expected[0] = data;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });

  ASSERT_TRUE(t2.Start());

  // Verify that we saw the dirty request.
  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));

  // This should reset the page state to dirty so that it is not moved to clean when the writeback
  // ends later.
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));

  ASSERT_TRUE(t2.Wait());

  // Verify that the page is dirty.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Now end the writeback. This should *not* clean the page, as a write was accepted after
  // beginning the writeback.
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 0, 1));
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
}

// Tests that mapping write permissions are cleared as expected on writeback.
TEST(PagerWriteback, WritebackWithMapping) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  zx_vaddr_t ptr;
  // Map the vmo.
  ASSERT_OK(zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                       zx_system_get_page_size(), &ptr));

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, zx_system_get_page_size());
  });

  // Write to the vmo. This will be trapped and generate a dirty request.
  auto buf = reinterpret_cast<uint8_t*>(ptr);
  uint8_t data = 0xaa;
  TestThread t1([buf, data, &expected]() -> bool {
    *buf = data;
    expected[0] = data;
    return true;
  });

  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));

  // Dirty the page.
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  ASSERT_TRUE(t1.Wait());

  // Verify that the page is dirty.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Write to the page again. This should go through without any page faults / dirty requests.
  data = 0xbb;
  *buf = data;
  expected[0] = data;
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Start a writeback.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 0, 1));
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Write to the page again. This should result in a fault / dirty request.
  TestThread t2([buf]() -> bool {
    *buf = 0xcc;
    return true;
  });

  ASSERT_TRUE(t2.Start());

  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));

  // Fail the dirty request so the writeback can complete.
  ASSERT_TRUE(pager.FailPages(vmo, 0, 1));
  ASSERT_TRUE(t2.WaitForCrash(ptr, ZX_ERR_IO));

  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Complete the writeback, making the page clean.
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 0, 1));
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Write to the page again. This should again be trapped.
  data = 0xdd;
  TestThread t3([buf, data, &expected]() -> bool {
    *buf = data;
    expected[0] = data;
    return true;
  });

  ASSERT_TRUE(t3.Start());

  ASSERT_TRUE(t3.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));

  ASSERT_TRUE(t3.Wait());

  // The page is dirty.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that the zero page marker cannot be overwritten by another page, unless written to at which
// point it is forked.
TEST_WITH_AND_WITHOUT_TRAP_DIRTY(CannotOverwriteZeroPage, 0) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, create_option, &vmo));

  // Supply with empty source vmo so that the destination gets zero page markers.
  zx::vmo vmo_src;
  ASSERT_OK(zx::vmo::create(zx_system_get_page_size(), 0, &vmo_src));
  ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), 0, zx_system_get_page_size(), vmo_src, 0));

  // Verify that the pager vmo has no committed pages, i.e. it only has markers.
  zx_info_vmo_t info;
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(0, info.committed_bytes);

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);

  // No dirty pages yet.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Commit a page in the source to attempt another supply.
  uint8_t data = 0xaa;
  ASSERT_OK(vmo_src.write(&data, 0, sizeof(data)));

  // Supplying the same page again should not overwrite the zero page marker. The supply will
  // succeed as a no-op.
  ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), 0, zx_system_get_page_size(), vmo_src, 0));

  // No committed pages still.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(0, info.committed_bytes);

  // The VMO is still all zeros.
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Now write to the VMO. This should fork the zero page.
  TestThread t1([vmo, &expected]() -> bool {
    uint8_t data = 0xbb;
    expected[0] = data;
    return vmo->vmo().write(&data, 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());

  // Wait for and acknowledge the dirty request if configured to trap dirty transitions.
  if (create_option == ZX_VMO_TRAP_DIRTY) {
    ASSERT_TRUE(t1.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
    // Dirty the first page.
    ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  }

  ASSERT_TRUE(t1.Wait());

  // Verify that the pager vmo has one committed page now.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(zx_system_get_page_size(), info.committed_bytes);

  // Verify that the page is dirty.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Verify written data.
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that VMOs created without the ZX_VMO_TRAP_DIRTY flag track dirty pages as expected.
TEST(PagerWriteback, SimpleDirtyNoTrap) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  // Create a VMO without the ZX_VMO_TRAP_DIRTY flag.
  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmo(1, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  // No dirty pages yet.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Write to the page now. This should go through without blocking.
  uint8_t data = 0x77;
  expected[0] = data;
  ASSERT_OK(vmo->vmo().write(&data, 0, sizeof(data)));

  // We should now have one dirty page.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Verify written data.
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Begin writeback on the page.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 0, 1));

  // The page is still dirty.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // This should transition the page to clean, and a subsequent write should trigger
  // another dirty request.
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 0, 1));

  // No dirty pages after writeback end.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // Map the vmo.
  zx_vaddr_t ptr;
  ASSERT_OK(zx::vmar::root_self()->map(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, 0, vmo->vmo(), 0,
                                       zx_system_get_page_size(), &ptr));

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    zx::vmar::root_self()->unmap(ptr, zx_system_get_page_size());
  });

  // Write to the vmo again via the mapping.
  auto buf = reinterpret_cast<uint8_t*>(ptr);
  data = 0x55;
  *buf = data;
  expected[0] = data;

  // The page should get dirtied again.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // No dirty or read requests seen.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
}

// Tests that VMOs created without the ZX_VMO_TRAP_DIRTY flag track dirty pages as expected for a
// random mix of zero and non-zero pages.
TEST(PagerWriteback, DirtyNoTrapRandomOffsets) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  // Create a VMO without the ZX_VMO_TRAP_DIRTY flag.
  Vmo* vmo;
  constexpr uint64_t kNumPages = 10;
  ASSERT_TRUE(pager.CreateVmo(kNumPages, &vmo));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(kNumPages * zx_system_get_page_size(), 0);

  // Empty source vmo to supply with zero pages.
  zx::vmo vmo_src;
  ASSERT_OK(zx::vmo::create(zx_system_get_page_size(), 0, &vmo_src));

  // For each page offset, supply either a zero or a non-zero page.
  uint64_t non_zero_count = 0;
  for (uint64_t i = 0; i < kNumPages; i++) {
    if (rand() % 2) {
      non_zero_count++;
      ASSERT_TRUE(pager.SupplyPages(vmo, i, 1));
      vmo->GenerateBufferContents(expected.data() + i * zx_system_get_page_size(), 1, i);
    } else {
      ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), i * zx_system_get_page_size(),
                                           zx_system_get_page_size(), vmo_src, 0));
    }
  }

  // Only non-zero pages should be committed.
  zx_info_vmo_t info;
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(non_zero_count * zx_system_get_page_size(), info.committed_bytes);

  // No dirty pages yet.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));

  // Verify that we're able to write to the entire range regardless of the type of page. Alter the
  // expected contents to verify later.
  uint8_t data = 0x77;
  for (uint64_t i = 0; i < kNumPages; i++) {
    expected[i * zx_system_get_page_size()] = data++;
  }
  ASSERT_OK(vmo->vmo().write(expected.data(), 0, kNumPages * zx_system_get_page_size()));

  // All the pages should be committed and dirty now.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  ASSERT_EQ(kNumPages * zx_system_get_page_size(), info.committed_bytes);
  zx_vmo_dirty_range_t range = {.offset = 0, .length = kNumPages};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_TRUE(check_buffer_data(vmo, 0, kNumPages, expected.data(), true));
}

// Tests that adding the WRITE permission with zx_vmar_protect does not override read-only mappings
// required in order to track dirty transitions.
TEST_WITH_AND_WITHOUT_TRAP_DIRTY(DirtyAfterMapProtect, 0) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  // Create a temporary VMAR to work with.
  zx::vmar vmar;
  zx_vaddr_t base_addr;
  ASSERT_OK(zx::vmar::root_self()->allocate(ZX_VM_CAN_MAP_READ | ZX_VM_CAN_MAP_WRITE, 0,
                                            zx_system_get_page_size(), &vmar, &base_addr));

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, create_option, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Buffer to verify VMO contents later.
  std::vector<uint8_t> expected(zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);

  zx_vaddr_t ptr;
  // Map the vmo read-only first so that the protect step below is not a no-op.
  ASSERT_OK(vmar.map(ZX_VM_PERM_READ, 0, vmo->vmo(), 0, zx_system_get_page_size(), &ptr));

  auto unmap = fit::defer([&]() {
    // Cleanup the mapping we created.
    vmar.unmap(ptr, zx_system_get_page_size());
  });

  // Read the VMO through the mapping so that the hardware mapping is created.
  uint8_t data = *reinterpret_cast<uint8_t*>(ptr);
  ASSERT_EQ(data, expected[0]);

  // Add the write permission now. This will allow us to write to the VMO below.
  ASSERT_OK(vmar.protect(ZX_VM_PERM_READ | ZX_VM_PERM_WRITE, ptr, zx_system_get_page_size()));

  // Write to the vmo. This should trigger a write fault. If the protect above added the write
  // permission on the hardware mapping, this write will go through without generating a write
  // fault for dirty tracking.
  auto buf = reinterpret_cast<uint8_t*>(ptr);
  data = 0xaa;
  TestThread t([buf, data, &expected]() -> bool {
    *buf = data;
    expected[0] = data;
    return true;
  });

  ASSERT_TRUE(t.Start());

  if (create_option == ZX_VMO_TRAP_DIRTY) {
    ASSERT_TRUE(t.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
    // Dirty the page.
    ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  }
  ASSERT_TRUE(t.Wait());

  // Verify that the page is dirty.
  zx_vmo_dirty_range_t range = {.offset = 0, .length = 1};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_EQ(data, *buf);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that zero pages are supplied by the kernel for the newly extended range after a resize, and
// are not overwritten by a pager supply.
TEST_WITH_AND_WITHOUT_TRAP_DIRTY(ResizeSupplyZero, ZX_VMO_RESIZABLE) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(2, create_option, &vmo));

  // Resize the VMO up.
  ASSERT_TRUE(vmo->Resize(4));

  // Now try to access all the pages. The first two should result in read requests, but the last
  // two should be supplied with zeros without any read requests.
  TestThread t([vmo]() -> bool {
    uint8_t data[4 * zx_system_get_page_size()];
    return vmo->vmo().read(&data[0], 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t.Start());
  ASSERT_TRUE(t.WaitForBlocked());

  ASSERT_TRUE(pager.WaitForPageRead(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));
  ASSERT_TRUE(t.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 1, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.SupplyPages(vmo, 1, 1));

  // No more read requests seen for the newly extended range.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  ASSERT_TRUE(t.Wait());

  // Verify that the last two pages are zeros.
  std::vector<uint8_t> expected(4 * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 2, 0);
  ASSERT_TRUE(check_buffer_data(vmo, 0, 4, expected.data(), true));

  // Only two pages should be committed in the VMO.
  zx_info_vmo_t info;
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  EXPECT_EQ(2 * zx_system_get_page_size(), info.committed_bytes);

  // Supply pages in the newly extended range. This should be a no-op. Since the range is already
  // implicitly "supplied", another supply will be ignored.
  ASSERT_TRUE(pager.SupplyPages(vmo, 2, 2));
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  EXPECT_EQ(2 * zx_system_get_page_size(), info.committed_bytes);

  // Verify that the last two pages are still zero.
  ASSERT_TRUE(check_buffer_data(vmo, 0, 4, expected.data(), true));

  // Writes for this case are tested separately in ResizeDirtyRequest. Skip the rest.
  if (create_option & ZX_VMO_TRAP_DIRTY) {
    return;
  }

  // Write to the last two pages now.
  uint8_t data[2 * zx_system_get_page_size()];
  memset(data, 0xaa, sizeof(data));
  ASSERT_OK(vmo->vmo().write(data, 2 * zx_system_get_page_size(), sizeof(data)));

  // All four pages should be committed now.
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  EXPECT_EQ(4 * zx_system_get_page_size(), info.committed_bytes);

  // Verify the contents.
  memset(expected.data() + 2 * zx_system_get_page_size(), 0xaa, sizeof(data));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 4, expected.data(), true));

  // The last two pages should be dirty.
  zx_vmo_dirty_range_t range = {.offset = 2, .length = 2};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
}

// Tests that writing to the newly extended range after a resize can generate DIRTY requests as
// expected.
TEST(PagerWriteback, ResizeDirtyRequest) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(2, ZX_VMO_TRAP_DIRTY | ZX_VMO_RESIZABLE, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 2));

  // Resize the VMO up.
  ASSERT_TRUE(vmo->Resize(3));

  // Now try to write pages 1 and 2. We should see dirty requests for both.
  TestThread t1([vmo]() -> bool {
    uint8_t data[2 * zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    return vmo->vmo().write(&data[0], zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());
  ASSERT_TRUE(t1.WaitForBlocked());

  // No read requests seen.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  // Dirty request seen for the entire write range.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 1, 2, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 1, 2));

  ASSERT_TRUE(t1.Wait());

  // Verify the VMO contents. (Allocate a buffer large enough to reuse across all resizes.)
  std::vector<uint8_t> expected(8 * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);
  memset(expected.data() + zx_system_get_page_size(), 0xaa, 2 * zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));
  zx_info_vmo_t info;
  ASSERT_OK(vmo->vmo().get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr));
  EXPECT_EQ(3 * zx_system_get_page_size(), info.committed_bytes);

  // Verify that pages 1 and 2 are dirty.
  zx_vmo_dirty_range_t range = {.offset = 1, .length = 2};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Resize the VMO up again, and try writing to a page after a gap.
  ASSERT_TRUE(vmo->Resize(6));

  TestThread t2([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xbb, sizeof(data));
    // Write to page 4.
    return vmo->vmo().write(&data[0], 4 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());

  // No read requests seen.
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  // We should only see a dirty request for page 4.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 4, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 4, 1));

  ASSERT_TRUE(t2.Wait());

  // Verify the contents again.
  memset(expected.data() + 4 * zx_system_get_page_size(), 0xbb, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 6, expected.data(), true));

  // Verify dirty ranges.
  zx_vmo_dirty_range_t ranges[] = {
      {1, 2, 0}, {3, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}, {4, 1, 0}, {5, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges, sizeof(ranges) / sizeof(zx_vmo_dirty_range_t)));

  // Resize up again, and try writing to the entire VMO at once.
  ASSERT_TRUE(vmo->Resize(8));

  TestThread t3([vmo]() -> bool {
    uint8_t data[8 * zx_system_get_page_size()];
    memset(data, 0xcc, sizeof(data));
    return vmo->vmo().write(&data[0], 0, sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t3.Start());
  ASSERT_TRUE(t3.WaitForBlocked());

  // No read requests seen.
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));

  // We should see a dirty request for page 0.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
  ASSERT_TRUE(t3.WaitForBlocked());

  // We should see a dirty request for page 3.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 3, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 3, 1));
  ASSERT_TRUE(t3.WaitForBlocked());

  // We should see a dirty request for pages 5,6,7.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 5, 3, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 5, 3));

  ASSERT_TRUE(t3.Wait());

  // Verify the contents.
  memset(expected.data(), 0xcc, 8 * zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 8, expected.data(), true));

  // Verify that all the pages are dirty.
  range = {.offset = 0, .length = 8};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
}

// Tests that writeback on a resized VMO works as expected.
TEST_WITH_AND_WITHOUT_TRAP_DIRTY(ResizeWriteback, ZX_VMO_RESIZABLE) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, create_option, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Resize the VMO up.
  ASSERT_TRUE(vmo->Resize(3));

  // Write to the first and the last page, leaving a gap in between.
  TestThread t([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    if (vmo->vmo().write(&data[0], 0, sizeof(data)) != ZX_OK) {
      return false;
    }
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t.Start());

  if (create_option & ZX_VMO_TRAP_DIRTY) {
    ASSERT_TRUE(t.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 0, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, 0, 1));
    ASSERT_TRUE(t.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, 2, 1));
  }
  ASSERT_TRUE(t.Wait());

  // Verify VMO contents.
  std::vector<uint8_t> expected(3 * zx_system_get_page_size(), 0xaa);
  memset(expected.data() + zx_system_get_page_size(), 0, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));

  // Verify that all the pages are dirty.
  zx_vmo_dirty_range_t ranges_before[] = {{0, 1, 0}, {1, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}, {2, 1, 0}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges_before,
                                      sizeof(ranges_before) / sizeof(zx_vmo_dirty_range_t)));

  // Attempt to writeback all the pages.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 0, 3));
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 0, 3));

  // All pages should be clean now.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // Verify VMO contents.
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));
}

// Tests that a resize down unblocks outstanding DIRTY requests that are out-of-bounds.
TEST(PagerWriteback, ResizeWithOutstandingDirtyRequests) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(5, ZX_VMO_RESIZABLE | ZX_VMO_TRAP_DIRTY, &vmo));

  // Supply page 1 as a zero page marker.
  zx::vmo vmo_src;
  ASSERT_OK(zx::vmo::create(zx_system_get_page_size(), 0, &vmo_src));
  ASSERT_OK(pager.pager().supply_pages(vmo->vmo(), zx_system_get_page_size(),
                                       zx_system_get_page_size(), vmo_src, 0));

  // Supply page 3 as an actual page.
  ASSERT_TRUE(pager.SupplyPages(vmo, 3, 1));

  // Resize the VMO up so there's a non-zero range that will be supplied as zero.
  ASSERT_TRUE(vmo->Resize(6));

  // The new "page" at the end should be indicated dirty and zero.
  zx_vmo_dirty_range_t range = {.offset = 5, .length = 1, .options = ZX_VMO_DIRTY_RANGE_IS_ZERO};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Try to write to page 1 which is a zero marker.
  TestThread t1([vmo]() -> bool {
    uint8_t data = 0xaa;
    return vmo->vmo().write(&data, zx_system_get_page_size(), sizeof(data)) == ZX_ERR_OUT_OF_RANGE;
  });

  // Try to write to page 3 which is an actual clean page.
  TestThread t2([vmo]() -> bool {
    uint8_t data = 0xbb;
    return vmo->vmo().write(&data, 3 * zx_system_get_page_size(), sizeof(data)) ==
           ZX_ERR_OUT_OF_RANGE;
  });

  // Try to write to page 5 which is a gap in the newly extended range.
  TestThread t3([vmo]() -> bool {
    uint8_t data = 0xcc;
    return vmo->vmo().write(&data, 5 * zx_system_get_page_size(), sizeof(data)) ==
           ZX_ERR_OUT_OF_RANGE;
  });

  // Try to read page 2 which is a non-resident page.
  TestThread t4([vmo]() -> bool {
    uint8_t data;
    return vmo->vmo().read(&data, 2 * zx_system_get_page_size(), sizeof(data)) ==
           ZX_ERR_OUT_OF_RANGE;
  });

  // All four threads should block.
  ASSERT_TRUE(t1.Start());
  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(t3.Start());
  ASSERT_TRUE(t3.WaitForBlocked());
  ASSERT_TRUE(t4.Start());
  ASSERT_TRUE(t4.WaitForBlocked());

  // We should see dirty requests for pages 1, 3 and 5.
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 1, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 3, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 5, 1, ZX_TIME_INFINITE));

  // We should see a read request for page 2.
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 2, 1, ZX_TIME_INFINITE));

  // No more requests seen.
  uint64_t offset, length;
  ASSERT_FALSE(pager.GetPageReadRequest(vmo, 0, &offset, &length));
  ASSERT_FALSE(pager.GetPageDirtyRequest(vmo, 0, &offset, &length));

  // Now resize down so that the pages all four threads are waiting for become out-of-bounds.
  ASSERT_TRUE(vmo->Resize(1));

  // All four threads should now see ZX_ERR_OUT_OF_RANGE returned for their reads/writes.
  ASSERT_TRUE(t1.Wait());
  ASSERT_TRUE(t2.Wait());
  ASSERT_TRUE(t3.Wait());
  ASSERT_TRUE(t4.Wait());

  // Trying to resolve the dirty and read requests we previously saw should fail.
  ASSERT_FALSE(pager.DirtyPages(vmo, 1, 1));
  ASSERT_FALSE(pager.DirtyPages(vmo, 3, 1));
  ASSERT_FALSE(pager.DirtyPages(vmo, 5, 1));
  ASSERT_FALSE(pager.SupplyPages(vmo, 2, 1));

  // The VMO has no dirty pages.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
}

// Tests that a resize down unblocks outstanding DIRTY requests that are out-of-bounds when the
// out-of-bounds range is in the process of being written back.
TEST(PagerWriteback, ResizeWritebackWithOutstandingDirtyRequests) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_RESIZABLE | ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Resize the VMO up.
  ASSERT_TRUE(vmo->Resize(3));

  // Write to a page leaving a gap.
  TestThread t1([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 2, 1));
  ASSERT_TRUE(t1.Wait());

  // Verify dirty ranges and VMO contents.
  zx_vmo_dirty_range_t ranges[] = {{1, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}, {2, 1, 0}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges, sizeof(ranges) / sizeof(zx_vmo_dirty_range_t)));

  std::vector<uint8_t> expected(3 * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);
  memset(expected.data() + 2 * zx_system_get_page_size(), 0xaa, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));

  // Beging writeback for all the dirty pages.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 1, 2));

  // Try to write to page 1. This will trigger a DIRTY request.
  TestThread t2([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xbb, sizeof(data));
    return vmo->vmo().write(&data[0], zx_system_get_page_size(), sizeof(data)) ==
           ZX_ERR_OUT_OF_RANGE;
  });
  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 1, 1, ZX_TIME_INFINITE));

  // Try to write to page 2. This will trigger a DIRTY request.
  TestThread t3([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xcc, sizeof(data));
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) ==
           ZX_ERR_OUT_OF_RANGE;
  });
  ASSERT_TRUE(t3.Start());
  ASSERT_TRUE(t3.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));

  // Resize down so that both the DIRTY requests are now out of bounds.
  ASSERT_TRUE(vmo->Resize(1));

  // Wait for the threads to complete.
  ASSERT_TRUE(t2.Wait());
  ASSERT_TRUE(t3.Wait());

  // Verify dirty ranges and VMO contents.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));

  // End the writeback we began previously. This will fail as it is out of bounds.
  ASSERT_FALSE(pager.WritebackEndPages(vmo, 1, 2));

  // Verify dirty ranges and VMO contents again.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 1, expected.data(), true));
}

// Tests that writing again to resized range that is being written back triggers new DIRTY requests.
TEST(PagerWriteback, ResizeWritebackNewDirtyRequestsInterleaved) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_RESIZABLE | ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Resize the VMO up.
  ASSERT_TRUE(vmo->Resize(3));

  // Write to a page leaving a gap.
  TestThread t1([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 2, 1));
  ASSERT_TRUE(t1.Wait());

  // Verify dirty ranges and VMO contents.
  zx_vmo_dirty_range_t ranges[] = {{1, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}, {2, 1, 0}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges, sizeof(ranges) / sizeof(zx_vmo_dirty_range_t)));

  std::vector<uint8_t> expected(3 * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);
  memset(expected.data() + 2 * zx_system_get_page_size(), 0xaa, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));

  // Beging writeback for all the dirty pages.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 1, 2));

  // Try to write to page 1. This will trigger a DIRTY request.
  TestThread t2([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xbb, sizeof(data));
    return vmo->vmo().write(&data[0], zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 1, 1, ZX_TIME_INFINITE));

  // Try to write to page 2. This will trigger a DIRTY request.
  TestThread t3([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xcc, sizeof(data));
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t3.Start());
  ASSERT_TRUE(t3.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));

  // Resolve the DIRTY requests and wait for the threads to complete.
  ASSERT_TRUE(pager.DirtyPages(vmo, 1, 2));
  ASSERT_TRUE(t2.Wait());
  ASSERT_TRUE(t3.Wait());

  // Verify dirty ranges and VMO contents.
  zx_vmo_dirty_range_t range = {1, 2, 0};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  memset(expected.data() + zx_system_get_page_size(), 0xbb, zx_system_get_page_size());
  memset(expected.data() + 2 * zx_system_get_page_size(), 0xcc, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));

  // End the writeback we began previously. This will be a no-op as both pages were dirtied again.
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 1, 2));

  // Verify dirty ranges and VMO contents again.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));

  // Should be able to write to the two dirty pages again without blocking.
  uint8_t data[2 * zx_system_get_page_size()];
  memset(data, 0xdd, sizeof(data));
  ASSERT_OK(vmo->vmo().write(&data[0], zx_system_get_page_size(), sizeof(data)));

  // Verify dirty ranges and VMO contents again.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));
  memset(expected.data() + zx_system_get_page_size(), 0xdd, 2 * zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));
}

// Tests that writing again to a written back resized range triggers new DIRTY requests.
TEST(PagerWriteback, ResizeWritebackNewDirtyRequests) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, ZX_VMO_RESIZABLE | ZX_VMO_TRAP_DIRTY, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Resize the VMO up.
  ASSERT_TRUE(vmo->Resize(3));

  // Write to a page leaving a gap.
  TestThread t1([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t1.Start());

  ASSERT_TRUE(t1.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.DirtyPages(vmo, 2, 1));
  ASSERT_TRUE(t1.Wait());

  // Verify dirty ranges and VMO contents.
  zx_vmo_dirty_range_t ranges[] = {{1, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}, {2, 1, 0}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges, sizeof(ranges) / sizeof(zx_vmo_dirty_range_t)));

  std::vector<uint8_t> expected(3 * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);
  memset(expected.data() + 2 * zx_system_get_page_size(), 0xaa, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));

  // Writeback all the dirty pages.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 1, 2));
  ASSERT_TRUE(pager.WritebackEndPages(vmo, 1, 2));

  // No dirty ranges remaining.
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, nullptr, 0));

  // Try to write to page 1. This will trigger a DIRTY request.
  TestThread t2([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xbb, sizeof(data));
    return vmo->vmo().write(&data[0], zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t2.Start());
  ASSERT_TRUE(t2.WaitForBlocked());
  // This was a gap that we've written back. So we'll first need to supply the page.
  ASSERT_TRUE(pager.WaitForPageRead(vmo, 1, 1, ZX_TIME_INFINITE));
  ASSERT_TRUE(pager.SupplyPages(vmo, 1, 1));
  ASSERT_TRUE(t2.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 1, 1, ZX_TIME_INFINITE));

  // Try to write to page 2. This will trigger a DIRTY request.
  TestThread t3([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xcc, sizeof(data));
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });
  ASSERT_TRUE(t3.Start());
  ASSERT_TRUE(t3.WaitForBlocked());
  ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));

  // Resolve the DIRTY requests and wait for the threads to complete.
  ASSERT_TRUE(pager.DirtyPages(vmo, 1, 2));
  ASSERT_TRUE(t2.Wait());
  ASSERT_TRUE(t3.Wait());

  // Verify dirty ranges and VMO contents.
  zx_vmo_dirty_range_t range = {1, 2, 0};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  memset(expected.data() + zx_system_get_page_size(), 0xbb, zx_system_get_page_size());
  memset(expected.data() + 2 * zx_system_get_page_size(), 0xcc, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 3, expected.data(), true));
}

// Tests that a write interleaved with a writeback trims / resets an awaiting clean zero range if it
// intersects it.
TEST_WITH_AND_WITHOUT_TRAP_DIRTY(ResizeWritebackIntersectingWrite, ZX_VMO_RESIZABLE) {
  UserPager pager;
  ASSERT_TRUE(pager.Init());

  Vmo* vmo;
  ASSERT_TRUE(pager.CreateVmoWithOptions(1, create_option, &vmo));
  ASSERT_TRUE(pager.SupplyPages(vmo, 0, 1));

  // Resize the VMO up.
  ASSERT_TRUE(vmo->Resize(4));

  // Newly extended range should be dirty and zero.
  zx_vmo_dirty_range_t range = {1, 3, ZX_VMO_DIRTY_RANGE_IS_ZERO};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, &range, 1));

  // Start writeback for the dirty range.
  ASSERT_TRUE(pager.WritebackBeginPages(vmo, 1, 3));

  // Write to a page in the range, leaving a gap, such that the awaiting clean zero range gets
  // trimmed.
  TestThread t1([vmo]() -> bool {
    uint8_t data[zx_system_get_page_size()];
    memset(data, 0xaa, sizeof(data));
    return vmo->vmo().write(&data[0], 2 * zx_system_get_page_size(), sizeof(data)) == ZX_OK;
  });

  ASSERT_TRUE(t1.Start());
  if (create_option & ZX_VMO_TRAP_DIRTY) {
    ASSERT_TRUE(t1.WaitForBlocked());
    ASSERT_TRUE(pager.WaitForPageDirty(vmo, 2, 1, ZX_TIME_INFINITE));
    ASSERT_TRUE(pager.DirtyPages(vmo, 2, 1));
  }
  ASSERT_TRUE(t1.Wait());

  // Verify VMO contents.
  std::vector<uint8_t> expected(4 * zx_system_get_page_size(), 0);
  vmo->GenerateBufferContents(expected.data(), 1, 0);
  memset(expected.data() + 2 * zx_system_get_page_size(), 0xaa, zx_system_get_page_size());
  ASSERT_TRUE(check_buffer_data(vmo, 0, 4, expected.data(), true));

  // Verify that the last three pages are dirty.
  zx_vmo_dirty_range_t ranges_before[] = {
      {1, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}, {2, 1, 0}, {3, 1, ZX_VMO_DIRTY_RANGE_IS_ZERO}};
  ASSERT_TRUE(pager.VerifyDirtyRanges(vmo, ranges_before,
                                      sizeof(ranges_before) /