[PATCH v2] OvmfPkg: Create additional PML1 entries for large SEV-SNP VMs

["Mikolaj Lisik" <lisik@google.com>]

Edk2 was failing, rather than creating more PML4 entries, when they
weren't present in the initial memory acceptance flow. Because of that
VMs with more than 512G memory were crashing. This code fixes that.

This change affects only SEV-SNP VMs.

The code was tested by successfully booting a 512G SEV-SNP VM.

Signed-off-by: Mikolaj Lisik <lisik@google.com>
---
 .../X64/PeiDxeVirtualMemory.c                 | 26 ++++++++++++-------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
index b9c0a5b25a..75c2c36bb4 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
@@ -548,6 +548,7 @@ InternalMemEncryptSevCreateIdentityMap1G (
   PAGE_MAP_AND_DIRECTORY_POINTER  *PageMapLevel4Entry;
   PAGE_TABLE_1G_ENTRY             *PageDirectory1GEntry;
   UINT64                          PgTableMask;
+  UINT64                          *NewPageTable;
   UINT64                          AddressEncMask;
   BOOLEAN                         IsWpEnabled;
   RETURN_STATUS                   Status;
@@ -602,15 +603,22 @@ InternalMemEncryptSevCreateIdentityMap1G (
     PageMapLevel4Entry  = (VOID *)(Cr3BaseAddress & ~PgTableMask);
     PageMapLevel4Entry += PML4_OFFSET (PhysicalAddress);
     if (!PageMapLevel4Entry->Bits.Present) {
-      DEBUG ((
-        DEBUG_ERROR,
-        "%a:%a: bad PML4 for Physical=0x%Lx\n",
-        gEfiCallerBaseName,
-        __FUNCTION__,
-        PhysicalAddress
-        ));
-      Status = RETURN_NO_MAPPING;
-      goto Done;
+      NewPageTable = AllocatePageTableMemory (1);
+      if (NewPageTable == NULL) {
+        DEBUG ((
+          DEBUG_ERROR,
+          "%a:%a: failed to allocate a new PML4 entry\n",
+          gEfiCallerBaseName,
+          __FUNCTION__
+          ));
+        Status = RETURN_NO_MAPPING;
+        goto Done;
+      }
+      SetMem (NewPageTable, EFI_PAGE_SIZE, 0);
+      PageMapLevel4Entry->Uint64          = (UINT64)(UINTN)NewPageTable | AddressEncMask;
+      PageMapLevel4Entry->Bits.MustBeZero = 0;
+      PageMapLevel4Entry->Bits.ReadWrite  = 1;
+      PageMapLevel4Entry->Bits.Present    = 1;
     }
 
     PageDirectory1GEntry = (VOID *)(
-- 
2.39.1.456.gfc5497dd1b-goog