[edk2-devel] [PATCH v2 14/15] OvmfPkg/PlatformPei: Reserve GHCB backup pages if S3 is supported

[Lendacky, Thomas]

From: Tom Lendacky <thomas.lendacky at amd.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3108

Protect the GHCB backup pages used by an SEV-ES guest when S3 is
supported.

Regarding the lifecycle of the GHCB backup pages:
  PcdOvmfSecGhcbBackupBase

(a) when and how it is initialized after first boot of the VM

  If SEV-ES is enabled, the GHCB backup pages are initialized when a
  nested #VC is received during the SEC phase
  [OvmfPkg/Library/VmgExitLib/SecVmgExitVcHandler.c].

(b) how it is protected from memory allocations during DXE

  If S3 and SEV-ES are enabled, then InitializeRamRegions()
  [OvmfPkg/PlatformPei/MemDetect.c] protects the ranges with an AcpiNVS
  memory allocation HOB, in PEI.

  If S3 is disabled, then these ranges are not protected. PEI switches to
  the GHCB backup pages in permanent PEI memory and DXE will use these
  PEI GHCB backup pages, so we don't have to preserve
  PcdOvmfSecGhcbBackupBase.

(c) how it is protected from the OS

  If S3 is enabled, then (b) reserves it from the OS too.

  If S3 is disabled, then the range needs no protection.

(d) how it is accessed on the S3 resume path

  It is rewritten same as in (a), which is fine because (b) reserved it.

(e) how it is accessed on the warm reset path

  It is rewritten same as in (a).

Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Laszlo Ersek <lersek at redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel at arm.com>
Cc: Anthony Perard <anthony.perard at citrix.com>
Cc: Julien Grall <julien at xen.org>
Cc: Brijesh Singh <brijesh.singh at amd.com>
Reviewed-by: Laszlo Ersek <lersek at redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
---
 OvmfPkg/PlatformPei/PlatformPei.inf | 2 ++
 OvmfPkg/PlatformPei/MemDetect.c     | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index c53be2f4925c..6ef77ba7bb21 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -118,6 +118,8 @@ [FixedPcd]
   gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
   gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiRuntimeServicesCode
   gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiRuntimeServicesData
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupSize
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaSize
 
diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
index ffbbef891a11..c08aa2e45a53 100644
--- a/OvmfPkg/PlatformPei/MemDetect.c
+++ b/OvmfPkg/PlatformPei/MemDetect.c
@@ -888,6 +888,11 @@ InitializeRamRegions (
         (UINT64)(UINTN) PcdGet32 (PcdOvmfSecGhcbSize),
         EfiACPIMemoryNVS
         );
+      BuildMemoryAllocationHob (
+        (EFI_PHYSICAL_ADDRESS)(UINTN) PcdGet32 (PcdOvmfSecGhcbBackupBase),
+        (UINT64)(UINTN) PcdGet32 (PcdOvmfSecGhcbBackupSize),
+        EfiACPIMemoryNVS
+        );
     }
 #endif
   }
-- 
2.30.0



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