Re: [PATCH v5 1/7] OvmfPkg: Realize EfiMemoryAcceptProtocol in AmdSevDxe

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

On 9/30/22 18:06, Dionna Glaze wrote:
> From: Sophia Wolf <phiawolf@google.com>
> 
> When a guest OS does not support unaccepted memory, the unaccepted
> memory must be accepted before returning a memory map to the caller.
> 
> EfiMemoryAcceptProtocol is defined in MdePkg and is implemented /
> Installed in AmdSevDxe for AMD SEV-SNP memory acceptance.
> 
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Dionna Glaze <dionnaglaze@google.com>

Just some formatting suggestions and one area of cleanup from previous 
version of the patch below. Assuming you take care of those:

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

> ---
>   OvmfPkg/AmdSevDxe/AmdSevDxe.c                                      | 57 ++++++++++++++++++--
>   OvmfPkg/AmdSevDxe/AmdSevDxe.inf                                    |  3 ++
>   OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c | 24 +++++++--
>   3 files changed, 76 insertions(+), 8 deletions(-)
> 
> diff --git a/OvmfPkg/AmdSevDxe/AmdSevDxe.c b/OvmfPkg/AmdSevDxe/AmdSevDxe.c
> index 662d3c4ccb..77d3caa833 100644
> --- a/OvmfPkg/AmdSevDxe/AmdSevDxe.c
> +++ b/OvmfPkg/AmdSevDxe/AmdSevDxe.c
> @@ -20,6 +20,7 @@
>   #include <Library/UefiBootServicesTableLib.h>
>   #include <Guid/ConfidentialComputingSevSnpBlob.h>
>   #include <Library/PcdLib.h>
> +#include <Protocol/MemoryAccept.h>
>   
>   STATIC CONFIDENTIAL_COMPUTING_SNP_BLOB_LOCATION  mSnpBootDxeTable = {
>     SIGNATURE_32 ('A',                                    'M', 'D', 'E'),
> @@ -31,6 +32,38 @@ STATIC CONFIDENTIAL_COMPUTING_SNP_BLOB_LOCATION  mSnpBootDxeTable = {
>     FixedPcdGet32 (PcdOvmfCpuidSize),
>   };
>   
> +STATIC EFI_HANDLE mAmdSevDxeHandle = NULL;
> +
> +STATIC
> +EFI_STATUS
> +EFIAPI
> +AmdSevMemoryAccept (
> +  IN EFI_MEMORY_ACCEPT_PROTOCOL *This,
> +  IN EFI_PHYSICAL_ADDRESS StartAddress,
> +  IN UINTN Size
> +)
> +{
> +  //
> +  // The StartAddress must be page-aligned, and the Size must be a positive
> +  // multiple of SIZE_4KB. Use an assert instead of returning an erros since
> +  // this is an EDK2-internal protocol.
> +  //
> +  ASSERT (((StartAddress & ~(SIZE_4KB - 1)) == 0) &&
> +          ((Size & ~(SIZE_4KB - 1)) == 0) &&
> +          (Size != 0));

Create a generic alignment check macro?

#define IS_ALIGNED(x, y)  (((x) & ((y) - 1)) == 0)

Maybe keep the ASSERTs separate so they better identify which condition 
caused the assert, e.g.:

   ASSERT (IS_ALIGNED (StartAddress, SIZE_4KB));
   ASSERT (IS_ALIGNED (Size, SIZE_4KB));
   ASSERT (Size != 0);

?

Not sure if those are worth it or not, though.

> +
> +  MemEncryptSevSnpPreValidateSystemRam (
> +    StartAddress,
> +    EFI_SIZE_TO_PAGES (Size)
> +    );
> +
> +  return EFI_SUCCESS;
> +}
> +
> +STATIC EFI_MEMORY_ACCEPT_PROTOCOL mMemoryAcceptProtocol = {
> +  AmdSevMemoryAccept
> +};
> +
>   EFI_STATUS
>   EFIAPI
>   AmdSevDxeEntryPoint (
> @@ -147,11 +180,27 @@ AmdSevDxeEntryPoint (
>       }
>     }
>   
> -  //
> -  // If its SEV-SNP active guest then install the CONFIDENTIAL_COMPUTING_SEV_SNP_BLOB.
> -  // It contains the location for both the Secrets and CPUID page.
> -  //
> +  if (EFI_ERROR (Status)) {
> +    DEBUG ((DEBUG_ERROR, "Install EfiMemoryAcceptProtocol failed.\n"));
> +  }

Looks like this shouldn't be here.

> +
>     if (MemEncryptSevSnpIsEnabled ()) {
> +    //
> +    // Memory acceptance began being required in SEV-SNP, so install the
> +    // memory accept protocol implementation for a SEV-SNP active guest.
> +    //
> +    Status = gBS->InstallProtocolInterface (
> +                  &mAmdSevDxeHandle,
> +                  &gEfiMemoryAcceptProtocolGuid,
> +                  EFI_NATIVE_INTERFACE,
> +                  &mMemoryAcceptProtocol
> +                  );

Need to indent these two more spaces to align with the "s" in Install.

Thanks,
Tom

> +    ASSERT_EFI_ERROR (Status);
> +
> +    //
> +    // If its SEV-SNP active guest then install the CONFIDENTIAL_COMPUTING_SEV_SNP_BLOB.
> +    // It contains the location for both the Secrets and CPUID page.
> +    //
>       return gBS->InstallConfigurationTable (
>                     &gConfidentialComputingSevSnpBlobGuid,
>                     &mSnpBootDxeTable
> diff --git a/OvmfPkg/AmdSevDxe/AmdSevDxe.inf b/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
> index 9acf860cf2..5ddddabc32 100644
> --- a/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
> +++ b/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
> @@ -47,6 +47,9 @@
>     gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsBase
>     gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsSize
>   
> +[Protocols]
> +  gEfiMemoryAcceptProtocolGuid
> +
>   [Guids]
>     gConfidentialComputingSevSnpBlobGuid
>   
> diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c
> index d3a95e4913..ee3710f7b3 100644
> --- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c
> +++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c
> @@ -14,6 +14,7 @@
>   #include <Library/MemEncryptSevLib.h>
>   
>   #include "SnpPageStateChange.h"
> +#include "VirtualMemory.h"
>   
>   /**
>     Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
> @@ -29,12 +30,27 @@ MemEncryptSevSnpPreValidateSystemRam (
>     IN UINTN             NumPages
>     )
>   {
> +  EFI_STATUS Status;
> +
>     if (!MemEncryptSevSnpIsEnabled ()) {
>       return;
>     }
>   
> -  //
> -  // All the pre-validation must be completed in the PEI phase.
> -  //
> -  ASSERT (FALSE);
> +  // DXE pre-validation may happen with the memory accept protocol.
> +  // The protocol should only be called outside the prevalidated ranges
> +  // that the PEI stage code explicitly skips. Specifically, only memory
> +  // ranges that are classified as unaccepted.
> +  if (BaseAddress >= SIZE_4GB) {
> +    Status = InternalMemEncryptSevCreateIdentityMap1G (
> +               0,
> +               BaseAddress,
> +               EFI_PAGES_TO_SIZE (NumPages)
> +               );
> +    if (EFI_ERROR (Status)) {
> +      ASSERT (FALSE);
> +      CpuDeadLoop ();
> +    }
> +  }
> +
> +  InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
>   }