OvmfPkg/PlatformPei: Retrieve APIC IDs from the hypervisor

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4654

If the hypervisor supports retrieval of the vCPU APIC IDs, retrieve
them before any APs are actually started. The APIC IDs can be used
to start the APs for any SEV-SNP guest, but is a requirement for an
SEV-SNP guest that is running under an SVSM.

After retrieving the APIC IDs, save the address of the APIC ID data
structure in a GUIDed HOB.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: Min Xu <min.m.xu@intel.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

OvmfPkg/PlatformPei/AmdSev.c

@@ -1,7 +1,7 @@
 /**@file
   Initialize Secure Encrypted Virtualization (SEV) support
 
-  Copyright (c) 2017 - 2020, Advanced Micro Devices. All rights reserved.<BR>
+  Copyright (c) 2017 - 2024, Advanced Micro Devices. All rights reserved.<BR>
 
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
@@ -9,6 +9,7 @@
 //
 // The package level header files this module uses
 //
+#include <Guid/GhcbApicIds.h>
 #include <IndustryStandard/Q35MchIch9.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/DebugLib.h>
@@ -31,6 +32,87 @@ GetHypervisorFeature (
   VOID
   );
 
+/**
+  Retrieve APIC IDs from the hypervisor.
+
+**/
+STATIC
+VOID
+AmdSevSnpGetApicIds (
+  VOID
+  )
+{
+  MSR_SEV_ES_GHCB_REGISTER  Msr;
+  GHCB                      *Ghcb;
+  BOOLEAN                   InterruptState;
+  UINT64                    VmgExitStatus;
+  UINT64                    PageCount;
+  BOOLEAN                   PageCountValid;
+  VOID                      *ApicIds;
+  RETURN_STATUS             Status;
+  UINT64                    GuidData;
+
+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+  Ghcb                    = Msr.Ghcb;
+
+  PageCount      = 0;
+  PageCountValid = FALSE;
+
+  CcExitVmgInit (Ghcb, &InterruptState);
+  Ghcb->SaveArea.Rax = PageCount;
+  CcExitVmgSetOffsetValid (Ghcb, GhcbRax);
+  VmgExitStatus = CcExitVmgExit (Ghcb, SVM_EXIT_GET_APIC_IDS, 0, 0);
+  if (CcExitVmgIsOffsetValid (Ghcb, GhcbRax)) {
+    PageCount      = Ghcb->SaveArea.Rax;
+    PageCountValid = TRUE;
+  }
+
+  CcExitVmgDone (Ghcb, InterruptState);
+
+  ASSERT (VmgExitStatus == 0);
+  ASSERT (PageCountValid);
+  if ((VmgExitStatus != 0) || !PageCountValid) {
+    return;
+  }
+
+  //
+  // Allocate the memory for the APIC IDs
+  //
+  ApicIds = AllocateReservedPages ((UINTN)PageCount);
+  ASSERT (ApicIds != NULL);
+
+  Status = MemEncryptSevClearPageEncMask (
+             0,
+             (UINTN)ApicIds,
+             (UINTN)PageCount
+             );
+  ASSERT_RETURN_ERROR (Status);
+
+  ZeroMem (ApicIds, EFI_PAGES_TO_SIZE ((UINTN)PageCount));
+
+  PageCountValid = FALSE;
+
+  CcExitVmgInit (Ghcb, &InterruptState);
+  Ghcb->SaveArea.Rax = PageCount;
+  CcExitVmgSetOffsetValid (Ghcb, GhcbRax);
+  VmgExitStatus = CcExitVmgExit (Ghcb, SVM_EXIT_GET_APIC_IDS, (UINTN)ApicIds, 0);
+  if (CcExitVmgIsOffsetValid (Ghcb, GhcbRax) && (Ghcb->SaveArea.Rax == PageCount)) {
+    PageCountValid = TRUE;
+  }
+
+  CcExitVmgDone (Ghcb, InterruptState);
+
+  ASSERT (VmgExitStatus == 0);
+  ASSERT (PageCountValid);
+  if ((VmgExitStatus != 0) || !PageCountValid) {
+    FreePages (ApicIds, (UINTN)PageCount);
+    return;
+  }
+
+  GuidData = (UINT64)(UINTN)ApicIds;
+  BuildGuidDataHob (&gGhcbApicIdsGuid, &GuidData, sizeof (GuidData));
+}
+
 /**
   Initialize SEV-SNP support if running as an SEV-SNP guest.
 
@@ -78,6 +160,14 @@ AmdSevSnpInitialize (
       }
     }
   }
+
+  //
+  // Retrieve the APIC IDs if the hypervisor supports it. These will be used
+  // to always start APs using SNP AP Create.
+  //
+  if ((HvFeatures & GHCB_HV_FEATURES_APIC_ID_LIST) == GHCB_HV_FEATURES_APIC_ID_LIST) {
+    AmdSevSnpGetApicIds ();
+  }
 }
 
 /**

OvmfPkg/PlatformPei/PlatformPei.inf

@@ -45,6 +45,7 @@
   gEfiMemoryTypeInformationGuid
   gFdtHobGuid
   gUefiOvmfPkgPlatformInfoGuid
+  gGhcbApicIdsGuid
 
 [LibraryClasses]
   BaseLib