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>

4 files changed, 185 insertions, 0 deletions

diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
index 717fd0ab1a..e9511eb40c 100644
--- a/OvmfPkg/XenPlatformPei/Platform.c
+++ b/OvmfPkg/XenPlatformPei/Platform.c
@@ -448,6 +448,7 @@ InitializeXenPlatform (
   InitializeRamRegions ();

 

   InitializeXen ();

+  CalibrateLapicTimer ();

 

   if (mBootMode != BOOT_ON_S3_RESUME) {

     ReserveEmuVariableNvStore ();

diff --git a/OvmfPkg/XenPlatformPei/Platform.h b/OvmfPkg/XenPlatformPei/Platform.h
index e70ca58078..77d88fc159 100644
--- a/OvmfPkg/XenPlatformPei/Platform.h
+++ b/OvmfPkg/XenPlatformPei/Platform.h
@@ -132,6 +132,11 @@ PhysicalAddressIdentityMapping (
   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 b2a7d1c21d..8b06bebd77 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 @@ PhysicalAddressIdentityMapping (
 

   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 8790d907d3..5732d21888 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]