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>

1 files changed, 43 insertions, 0 deletions

diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
index c6e1106c9e..0be86722e5 100644
--- a/OvmfPkg/PlatformPei/Platform.c
+++ b/OvmfPkg/PlatformPei/Platform.c
@@ -68,6 +68,7 @@ EFI_BOOT_MODE mBootMode = BOOT_WITH_FULL_CONFIGURATION;
 

 BOOLEAN mS3Supported = FALSE;

 

+UINT32 mMaxCpuCount;

 

 VOID

 AddIoMemoryBaseSizeHob (

@@ -568,6 +569,47 @@ 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.

 

   @param  FileHandle      Handle of the file being invoked.

@@ -601,6 +643,7 @@ InitializePlatform (
   S3Verification ();

   BootModeInitialization ();

   AddressWidthInitialization ();

+  MaxCpuCountInitialization ();

 

   PublishPeiMemory ();