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

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 1/26/23 14:26, Mikolaj Lisik wrote:
> 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>

Acked-by: Tom Lendacky <thomas.lendacky@amd.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 *)(