OvmfPkg/PlatformPei: take VCPU count from QEMU and configure MpInitLib

These settings will allow CpuMpPei and CpuDxe to wait for the initial AP
check-ins exactly as long as necessary.

It is safe to set PcdCpuMaxLogicalProcessorNumber and
PcdCpuApInitTimeOutInMicroSeconds in OvmfPkg/PlatformPei.
OvmfPkg/PlatformPei installs the permanent PEI RAM, producing
gEfiPeiMemoryDiscoveredPpiGuid, and UefiCpuPkg/CpuMpPei has a depex on
gEfiPeiMemoryDiscoveredPpiGuid.

It is safe to read the fw_cfg item QemuFwCfgItemSmpCpuCount (0x0005). It
was added to QEMU in 2008 as key FW_CFG_NB_CPUS, in commit 905fdcb5264c
("Add common keys to firmware configuration"). Even if the key is
unavailable (or if fw_cfg is entirely unavailable, for example on Xen),
QemuFwCfgRead16() will return 0, and then we stick with the current
behavior.

Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

OvmfPkg/OvmfPkgIa32.dsc

@@ -488,6 +488,10 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdPropertiesTableEnable|FALSE
 
+  # UefiCpuPkg PCDs related to initial AP bringup and general AP management.
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuMaxLogicalProcessorNumber|64
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuApInitTimeOutInMicroSeconds|50000
+
 ################################################################################
 #
 # Components Section - list of all EDK II Modules needed by this Platform.

OvmfPkg/OvmfPkgIa32X64.dsc

@@ -496,6 +496,10 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdPropertiesTableEnable|FALSE
 
+  # UefiCpuPkg PCDs related to initial AP bringup and general AP management.
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuMaxLogicalProcessorNumber|64
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuApInitTimeOutInMicroSeconds|50000
+
 ################################################################################
 #
 # Components Section - list of all EDK II Modules needed by this Platform.

OvmfPkg/OvmfPkgX64.dsc

@@ -495,6 +495,10 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdPropertiesTableEnable|FALSE
 
+  # UefiCpuPkg PCDs related to initial AP bringup and general AP management.
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuMaxLogicalProcessorNumber|64
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuApInitTimeOutInMicroSeconds|50000
+
 ################################################################################
 #
 # Components Section - list of all EDK II Modules needed by this Platform.

OvmfPkg/PlatformPei/MemDetect.c

@@ -358,7 +358,7 @@ PublishPeiMemory (
   //
   if (mS3Supported) {
     mS3AcpiReservedMemorySize = SIZE_512KB +
-      PcdGet32 (PcdCpuMaxLogicalProcessorNumber) *
+      mMaxCpuCount *
       PcdGet32 (PcdCpuApStackSize);
     mS3AcpiReservedMemoryBase = LowerMemorySize - mS3AcpiReservedMemorySize;
     LowerMemorySize = mS3AcpiReservedMemoryBase;

OvmfPkg/PlatformPei/Platform.c

@@ -68,6 +68,7 @@ EFI_BOOT_MODE mBootMode = BOOT_WITH_FULL_CONFIGURATION;
 
 BOOLEAN mS3Supported = FALSE;
 
+UINT32 mMaxCpuCount;
 
 VOID
 AddIoMemoryBaseSizeHob (
@@ -567,6 +568,47 @@ S3Verification (
 }
 
 
+/**
+  Fetch the number of boot CPUs from QEMU and expose it to UefiCpuPkg modules.
+  Set the mMaxCpuCount variable.
+**/
+VOID
+MaxCpuCountInitialization (
+  VOID
+  )
+{
+  UINT16        ProcessorCount;
+  RETURN_STATUS PcdStatus;
+
+  QemuFwCfgSelectItem (QemuFwCfgItemSmpCpuCount);
+  ProcessorCount = QemuFwCfgRead16 ();
+  //
+  // If the fw_cfg key or fw_cfg entirely is unavailable, load mMaxCpuCount
+  // from the PCD default. No change to PCDs.
+  //
+  if (ProcessorCount == 0) {
+    mMaxCpuCount = PcdGet32 (PcdCpuMaxLogicalProcessorNumber);
+    return;
+  }
+  //
+  // Otherwise, set mMaxCpuCount to the value reported by QEMU.
+  //
+  mMaxCpuCount = ProcessorCount;
+  //
+  // Additionally, tell UefiCpuPkg modules (a) the exact number of VCPUs, (b)
+  // to wait, in the initial AP bringup, exactly as long as it takes for all of
+  // the APs to report in. For this, we set the longest representable timeout
+  // (approx. 71 minutes).
+  //
+  PcdStatus = PcdSet32S (PcdCpuMaxLogicalProcessorNumber, ProcessorCount);
+  ASSERT_RETURN_ERROR (PcdStatus);
+  PcdStatus = PcdSet32S (PcdCpuApInitTimeOutInMicroSeconds, MAX_UINT32);
+  ASSERT_RETURN_ERROR (PcdStatus);
+  DEBUG ((DEBUG_INFO, "%a: QEMU reports %d processor(s)\n", __FUNCTION__,
+    ProcessorCount));
+}
+
+
 /**
   Perform Platform PEI initialization.
 
@@ -601,6 +643,7 @@ InitializePlatform (
   S3Verification ();
   BootModeInitialization ();
   AddressWidthInitialization ();
+  MaxCpuCountInitialization ();
 
   PublishPeiMemory ();
 

OvmfPkg/PlatformPei/Platform.h

@@ -101,4 +101,6 @@ extern BOOLEAN mS3Supported;
 
 extern UINT8 mPhysMemAddressWidth;
 
+extern UINT32 mMaxCpuCount;
+
 #endif // _PLATFORM_PEI_H_INCLUDED_

OvmfPkg/PlatformPei/PlatformPei.inf

@@ -95,6 +95,7 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdAcpiS3Enable
   gUefiCpuPkgTokenSpaceGuid.PcdCpuLocalApicBaseAddress
   gUefiCpuPkgTokenSpaceGuid.PcdCpuMaxLogicalProcessorNumber
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuApInitTimeOutInMicroSeconds
   gUefiCpuPkgTokenSpaceGuid.PcdCpuApStackSize
 
 [FixedPcd]