[PATCH v4 4/4] UefiCpuPkg: Store SEV-SNP AP jump table in the secrets page

["Roth, Michael" <Michael.Roth@amd.com>]

A full-featured SEV-SNP guest will not rely on the AP jump table, and
will instead use the AP Creation interface defined by the GHCB. However,
a guest is still allowed to use the AP jump table if desired.

However, unlike with SEV-ES guests, SEV-SNP guests should not
store/retrieve the jump table address via GHCB requests to the
hypervisor, they should instead store/retrieve it via the SEV-SNP
secrets page. Implement the store side of this for OVMF.

Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 UefiCpuPkg/Library/MpInitLib/DxeMpInitLib.inf |  1 +
 UefiCpuPkg/Library/MpInitLib/DxeMpLib.c       | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/UefiCpuPkg/Library/MpInitLib/DxeMpInitLib.inf b/UefiCpuPkg/Library/MpInitLib/DxeMpInitLib.inf
index 8c8b81d933..0c36538d59 100644
--- a/UefiCpuPkg/Library/MpInitLib/DxeMpInitLib.inf
+++ b/UefiCpuPkg/Library/MpInitLib/DxeMpInitLib.inf
@@ -85,3 +85,4 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard                      ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdGhcbBase                           ## CONSUMES
   gEfiMdePkgTokenSpaceGuid.PcdConfidentialComputingGuestAttr           ## CONSUMES
+  gEfiMdePkgTokenSpaceGuid.PcdSevSnpSecretsAddress                     ## CONSUMES
diff --git a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
index beab06a5b1..8edc612772 100644
--- a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
@@ -15,6 +15,7 @@
 #include <Library/CcExitLib.h>
 #include <Register/Amd/Fam17Msr.h>
 #include <Register/Amd/Ghcb.h>
+#include <Register/Amd/SnpSecretsPage.h>
 
 #include <Protocol/Timer.h>
 
@@ -217,6 +218,15 @@ GetSevEsAPMemory (
 
   DEBUG ((DEBUG_INFO, "Dxe: SevEsAPMemory = %lx\n", (UINTN)StartAddress));
 
+  if (ConfidentialComputingGuestHas (CCAttrAmdSevSnp)) {
+    SNP_SECRETS_PAGE  *Secrets;
+
+    Secrets                       = (SNP_SECRETS_PAGE *)(INTN)PcdGet64 (PcdSevSnpSecretsAddress);
+    Secrets->OsArea.ApJumpTablePa = (UINT64)(UINTN)StartAddress;
+
+    return (UINTN)StartAddress;
+  }
+
   //
   // Save the SevEsAPMemory as the AP jump table.
   //
-- 
2.25.1