OvmfPkg/XenPlatformPei: Calibrate APIC timer frequency
Calculate the frequency of the APIC timer that Xen provides.
Even though the frequency is currently hard-coded, it isn't part of
the public ABI that Xen provides and thus may change at any time. OVMF
needs to determine the frequency by an other mean.
Fortunately, Xen provides a way to determines the frequency of the
TSC, so we can use TSC to calibrate the frequency of the APIC timer.
That information is found in the shared_info page which we map and
unmap once done (XenBusDxe is going to map the page somewhere else).
The shared_info page is mapped at the highest physical address allowed
as it doesn't need to be in the RAM, thus there's a call to update the
page table.
The calculated frequency is only logged in this patch, it will be used
in a following patch.
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2490
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210412133003.146438-7-anthony.perard@citrix.com>
diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
index 717fd0a..e9511eb 100644
--- a/OvmfPkg/XenPlatformPei/Platform.c
+++ b/OvmfPkg/XenPlatformPei/Platform.c
@@ -448,6 +448,7 @@
InitializeRamRegions ();
InitializeXen ();
+ CalibrateLapicTimer ();
if (mBootMode != BOOT_ON_S3_RESUME) {
ReserveEmuVariableNvStore ();
diff --git a/OvmfPkg/XenPlatformPei/Platform.h b/OvmfPkg/XenPlatformPei/Platform.h
index e70ca58..77d88fc 100644
--- a/OvmfPkg/XenPlatformPei/Platform.h
+++ b/OvmfPkg/XenPlatformPei/Platform.h
@@ -132,6 +132,11 @@
IN EFI_PHYSICAL_ADDRESS AddressToMap
);
+VOID
+CalibrateLapicTimer (
+ VOID
+ );
+
extern EFI_BOOT_MODE mBootMode;
extern UINT8 mPhysMemAddressWidth;
diff --git a/OvmfPkg/XenPlatformPei/Xen.c b/OvmfPkg/XenPlatformPei/Xen.c
index b2a7d1c..8b06beb 100644
--- a/OvmfPkg/XenPlatformPei/Xen.c
+++ b/OvmfPkg/XenPlatformPei/Xen.c
@@ -21,8 +21,10 @@
#include <Library/CpuLib.h>
#include <Library/DebugLib.h>
#include <Library/HobLib.h>
+#include <Library/LocalApicLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/PcdLib.h>
+#include <Library/SafeIntLib.h>
#include <Guid/XenInfo.h>
#include <IndustryStandard/E820.h>
#include <Library/ResourcePublicationLib.h>
@@ -457,3 +459,178 @@
return EFI_SUCCESS;
}
+
+STATIC
+EFI_STATUS
+MapSharedInfoPage (
+ IN VOID *PagePtr
+ )
+{
+ xen_add_to_physmap_t Parameters;
+ INTN ReturnCode;
+
+ Parameters.domid = DOMID_SELF;
+ Parameters.space = XENMAPSPACE_shared_info;
+ Parameters.idx = 0;
+ Parameters.gpfn = (UINTN)PagePtr >> EFI_PAGE_SHIFT;
+ ReturnCode = XenHypercallMemoryOp (XENMEM_add_to_physmap, &Parameters);
+ if (ReturnCode != 0) {
+ return EFI_NO_MAPPING;
+ }
+ return EFI_SUCCESS;
+}
+
+STATIC
+VOID
+UnmapXenPage (
+ IN VOID *PagePtr
+ )
+{
+ xen_remove_from_physmap_t Parameters;
+ INTN ReturnCode;
+
+ Parameters.domid = DOMID_SELF;
+ Parameters.gpfn = (UINTN)PagePtr >> EFI_PAGE_SHIFT;
+ ReturnCode = XenHypercallMemoryOp (XENMEM_remove_from_physmap, &Parameters);
+ ASSERT (ReturnCode == 0);
+}
+
+
+STATIC
+UINT64
+GetCpuFreq (
+ IN XEN_VCPU_TIME_INFO *VcpuTime
+ )
+{
+ UINT32 Version;
+ UINT32 TscToSystemMultiplier;
+ INT8 TscShift;
+ UINT64 CpuFreq;
+
+ do {
+ Version = VcpuTime->Version;
+ MemoryFence ();
+ TscToSystemMultiplier = VcpuTime->TscToSystemMultiplier;
+ TscShift = VcpuTime->TscShift;
+ MemoryFence ();
+ } while (((Version & 1) != 0) && (Version != VcpuTime->Version));
+
+ CpuFreq = DivU64x32 (LShiftU64 (1000000000ULL, 32), TscToSystemMultiplier);
+ if (TscShift >= 0) {
+ CpuFreq = RShiftU64 (CpuFreq, TscShift);
+ } else {
+ CpuFreq = LShiftU64 (CpuFreq, -TscShift);
+ }
+ return CpuFreq;
+}
+
+STATIC
+VOID
+XenDelay (
+ IN XEN_VCPU_TIME_INFO *VcpuTimeInfo,
+ IN UINT64 DelayNs
+ )
+{
+ UINT64 Tick;
+ UINT64 CpuFreq;
+ UINT64 Delay;
+ UINT64 DelayTick;
+ UINT64 NewTick;
+ RETURN_STATUS Status;
+
+ Tick = AsmReadTsc ();
+
+ CpuFreq = GetCpuFreq (VcpuTimeInfo);
+ Status = SafeUint64Mult (DelayNs, CpuFreq, &Delay);
+ if (EFI_ERROR (Status)) {
+ DEBUG ((DEBUG_ERROR,
+ "XenDelay (%lu ns): delay too big in relation to CPU freq %lu Hz\n",
+ DelayNs, CpuFreq));
+ ASSERT_EFI_ERROR (Status);
+ CpuDeadLoop ();
+ }
+
+ DelayTick = DivU64x32 (Delay, 1000000000);
+
+ NewTick = Tick + DelayTick;
+
+ //
+ // Check for overflow
+ //
+ if (NewTick < Tick) {
+ //
+ // Overflow, wait for TSC to also overflow
+ //
+ while (AsmReadTsc () >= Tick) {
+ CpuPause ();
+ }
+ }
+
+ while (AsmReadTsc () <= NewTick) {
+ CpuPause ();
+ }
+}
+
+
+/**
+ Calculate the frequency of the Local Apic Timer
+**/
+VOID
+CalibrateLapicTimer (
+ VOID
+ )
+{
+ XEN_SHARED_INFO *SharedInfo;
+ XEN_VCPU_TIME_INFO *VcpuTimeInfo;
+ UINT32 TimerTick, TimerTick2, DiffTimer;
+ UINT64 TscTick, TscTick2;
+ UINT64 Freq;
+ UINT64 Dividend;
+ EFI_STATUS Status;
+
+
+ SharedInfo = (VOID*)((1ULL << mPhysMemAddressWidth) - EFI_PAGE_SIZE);
+ Status = PhysicalAddressIdentityMapping ((EFI_PHYSICAL_ADDRESS)SharedInfo);
+ if (EFI_ERROR (Status)) {
+ DEBUG ((DEBUG_ERROR,
+ "Failed to add page table entry for Xen shared info page: %r\n",
+ Status));
+ ASSERT_EFI_ERROR (Status);
+ return;
+ }
+
+ Status = MapSharedInfoPage (SharedInfo);
+ if (EFI_ERROR (Status)) {
+ DEBUG ((DEBUG_ERROR, "Failed to map Xen's shared info page: %r\n",
+ Status));
+ ASSERT_EFI_ERROR (Status);
+ return;
+ }
+
+ VcpuTimeInfo = &SharedInfo->VcpuInfo[0].Time;
+
+ InitializeApicTimer (1, MAX_UINT32, TRUE, 0);
+ DisableApicTimerInterrupt ();
+
+ TimerTick = GetApicTimerCurrentCount ();
+ TscTick = AsmReadTsc ();
+ XenDelay (VcpuTimeInfo, 1000000ULL);
+ TimerTick2 = GetApicTimerCurrentCount ();
+ TscTick2 = AsmReadTsc ();
+
+
+ DiffTimer = TimerTick - TimerTick2;
+ Status = SafeUint64Mult (GetCpuFreq (VcpuTimeInfo), DiffTimer, &Dividend);
+ if (EFI_ERROR (Status)) {
+ DEBUG ((DEBUG_ERROR, "overflow while calculating APIC frequency\n"));
+ DEBUG ((DEBUG_ERROR, "CPU freq: %lu Hz; APIC timer tick count for 1 ms: %u\n",
+ GetCpuFreq (VcpuTimeInfo), DiffTimer));
+ ASSERT_EFI_ERROR (Status);
+ CpuDeadLoop ();
+ }
+
+ Freq = DivU64x64Remainder (Dividend, TscTick2 - TscTick, NULL);
+ DEBUG ((DEBUG_INFO, "APIC Freq % 8lu Hz\n", Freq));
+
+ UnmapXenPage (SharedInfo);
+}
diff --git a/OvmfPkg/XenPlatformPei/XenPlatformPei.inf b/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
index 8790d90..5732d21 100644
--- a/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
+++ b/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
@@ -52,6 +52,7 @@
DebugLib
HobLib
IoLib
+ LocalApicLib
PciLib
ResourcePublicationLib
PeiServicesLib
@@ -59,6 +60,7 @@
MtrrLib
MemEncryptSevLib
PcdLib
+ SafeIntLib
XenHypercallLib
[Pcd]
