OvmfPkg/PlatformPei: mark cpuid and secrets memory reserved in EFI map

When SEV-SNP is active, the CPUID and Secrets memory range contains the
information that is used during the VM boot. The content need to be persist
across the kexec boot. Mark the memory range as Reserved in the EFI map
so that guest OS or firmware does not use the range as a system RAM.

Cc: Michael Roth <michael.roth@amd.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

OvmfPkg/PlatformPei/AmdSev.c

@@ -416,3 +416,34 @@ AmdSevInitialize (
 
   ASSERT_RETURN_ERROR (PcdStatus);
 }
+
+/**
+ The function performs SEV specific region initialization.
+
+ **/
+VOID
+SevInitializeRam (
+  VOID
+  )
+{
+  if (MemEncryptSevSnpIsEnabled ()) {
+    //
+    // If SEV-SNP is enabled, reserve the Secrets and CPUID memory area.
+    //
+    // This memory range is given to the PSP by the hypervisor to populate
+    // the information used during the SNP VM boots, and it need to persist
+    // across the kexec boots. Mark it as EfiReservedMemoryType so that
+    // the guest firmware and OS does not use it as a system memory.
+    //
+    BuildMemoryAllocationHob (
+      (EFI_PHYSICAL_ADDRESS)(UINTN)PcdGet32 (PcdOvmfSnpSecretsBase),
+      (UINT64)(UINTN)PcdGet32 (PcdOvmfSnpSecretsSize),
+      EfiReservedMemoryType
+      );
+    BuildMemoryAllocationHob (
+      (EFI_PHYSICAL_ADDRESS)(UINTN)PcdGet32 (PcdOvmfCpuidBase),
+      (UINT64)(UINTN)PcdGet32 (PcdOvmfCpuidSize),
+      EfiReservedMemoryType
+      );
+  }
+}