Re: [PATCH v4 4/4] OvmfPkg/PlatformDxe: Add support for SEV live migration.

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

On 6/21/21 8:57 AM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
> 
> Detect for KVM hypervisor and check for SEV live migration
> feature support via KVM_FEATURE_CPUID, if detected setup a new
> UEFI enviroment variable to indicate OVMF support for SEV
> live migration.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  OvmfPkg/Include/Guid/MemEncryptLib.h |  20 ++++
>  OvmfPkg/OvmfPkg.dec                  |   1 +
>  OvmfPkg/PlatformDxe/AmdSev.c         | 108 ++++++++++++++++++++
>  OvmfPkg/PlatformDxe/Platform.c       |   5 +
>  OvmfPkg/PlatformDxe/Platform.inf     |   2 +
>  OvmfPkg/PlatformDxe/PlatformConfig.h |   5 +
>  6 files changed, 141 insertions(+)
> 
> diff --git a/OvmfPkg/Include/Guid/MemEncryptLib.h b/OvmfPkg/Include/Guid/MemEncryptLib.h
> new file mode 100644
> index 0000000000..4c046ba439
> --- /dev/null
> +++ b/OvmfPkg/Include/Guid/MemEncryptLib.h
> @@ -0,0 +1,20 @@
> +/** @file
> +
> +  AMD Memory Encryption GUID, define a new GUID for defining
> +  new UEFI enviroment variables assocaiated with SEV Memory Encryption.
> +
> +  Copyright (c) 2020, AMD Inc. All rights reserved.<BR>
> +
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#ifndef __MEMENCRYPT_LIB_H__
> +#define __MEMENCRYPT_LIB_H__
> +
> +#define MEMENCRYPT_GUID \
> +{0x0cf29b71, 0x9e51, 0x433a, {0xa3, 0xb7, 0x81, 0xf3, 0xab, 0x16, 0xb8, 0x75}}
> +
> +extern EFI_GUID gMemEncryptGuid;
> +
> +#endif
> diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec
> index 6ae733f6e3..e452dc8494 100644
> --- a/OvmfPkg/OvmfPkg.dec
> +++ b/OvmfPkg/OvmfPkg.dec
> @@ -122,6 +122,7 @@
>    gQemuKernelLoaderFsMediaGuid          = {0x1428f772, 0xb64a, 0x441e, {0xb8, 0xc3, 0x9e, 0xbd, 0xd7, 0xf8, 0x93, 0xc7}}
>    gGrubFileGuid                         = {0xb5ae312c, 0xbc8a, 0x43b1, {0x9c, 0x62, 0xeb, 0xb8, 0x26, 0xdd, 0x5d, 0x07}}
>    gConfidentialComputingSecretGuid      = {0xadf956ad, 0xe98c, 0x484c, {0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47}}
> +  gMemEncryptGuid                       = {0x0cf29b71, 0x9e51, 0x433a, {0xa3, 0xb7, 0x81, 0xf3, 0xab, 0x16, 0xb8, 0x75}}
>  
>  [Ppis]
>    # PPI whose presence in the PPI database signals that the TPM base address
> diff --git a/OvmfPkg/PlatformDxe/AmdSev.c b/OvmfPkg/PlatformDxe/AmdSev.c
> new file mode 100644
> index 0000000000..3dbf17a8cd
> --- /dev/null
> +++ b/OvmfPkg/PlatformDxe/AmdSev.c

Can this be done in OvmfPkg/AmdSevDxe/AmdSevDxe.c or is that too early?

> @@ -0,0 +1,108 @@
> +/**@file
> +  Detect KVM hypervisor support for SEV live migration and if
> +  detected, setup a new UEFI enviroment variable indicating
> +  OVMF support for SEV live migration.
> +
> +  Copyright (c) 2020, Advanced Micro Devices. All rights reserved.<BR>
> +
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +//
> +// The package level header files this module uses
> +//
> +
> +#include <Library/BaseLib.h>
> +#include <Library/BaseMemoryLib.h>
> +#include <Library/DebugLib.h>
> +#include <Library/UefiBootServicesTableLib.h>
> +#include <Library/UefiRuntimeServicesTableLib.h>
> +#include <Guid/MemEncryptLib.h>
> +
> +#define KVM_FEATURE_MIGRATION_CONTROL   17

BIT17

> +
> +/**
> +  Figures out if we are running inside KVM HVM and
> +  KVM HVM supports SEV Live Migration feature.
> +
> +  @retval TRUE   KVM was detected and Live Migration supported
> +  @retval FALSE  KVM was not detected or Live Migration not supported
> +
> +**/
> +BOOLEAN
> +KvmDetectSevLiveMigrationFeature(
> +  VOID
> +  )
> +{
> +  UINT8 Signature[13];
> +  UINT32 mKvmLeaf = 0;
> +  UINT32 RegEax, RegEbx, RegEcx, RegEdx;
> +
> +  Signature[12] = '\0';
> +  for (mKvmLeaf = 0x40000000; mKvmLeaf < 0x40010000; mKvmLeaf += 0x100) {

What's the reason for the loop? I would think that just checking
0x40000000 would be enough, so a comment seems to be warranted.

> +    AsmCpuid (mKvmLeaf,
> +              NULL,
> +              (UINT32 *) &Signature[0],
> +              (UINT32 *) &Signature[4],
> +              (UINT32 *) &Signature[8]);
> +
> +    if (!AsciiStrCmp ((CHAR8 *) Signature, "KVMKVMKVM\0\0\0")) {
> +      DEBUG ((
> +        DEBUG_ERROR,

DEBUG_INFO, it doesn't seem like an error.

> +        "%a: KVM Detected, signature = %s\n",
> +        __FUNCTION__,
> +        Signature
> +        ));
> +> +      RegEax = 0x40000001;

Should this be mKvmLeaf + 1? It is confusing that you may check 0x40000100
and then not do 0x40000101.

> +      RegEcx = 0;
> +      AsmCpuid (0x40000001, &RegEax, &RegEbx, &RegEcx, &RegEdx);
> +      if (RegEax & (1 << KVM_FEATURE_MIGRATION_CONTROL)) {

This needs to be (assuming BIT17 is used above):

  if ((RegEax & KVM_FEATURE_MIGRATION_CONTROL) != 0) {

You must use an actual comparison if the variable is not a boolean.

> +        DEBUG ((
> +          DEBUG_ERROR,
> +          "%a: Live Migration feature supported\n",

DEBUG_INFO again.

> +          __FUNCTION__
> +          ));
> +        return TRUE;
> +      }
> +    }
> +  }
> +
> +  return FALSE;
> +}
> +
> +/**
> +
> +  Function checks if SEV Live Migration support is available, if present then it sets
> +  a UEFI enviroment variable to be queried later using Runtime services.
> +
> +  **/
> +VOID
> +AmdSevSetConfig(

Kind of a generic name for what is being done.

> +  VOID
> +  )
> +{
> +  EFI_STATUS Status;
> +  BOOLEAN SevLiveMigrationEnabled;
> +
> +  SevLiveMigrationEnabled = KvmDetectSevLiveMigrationFeature();
> +
> +  if (SevLiveMigrationEnabled) {
> +   Status = gRT->SetVariable (
> +                L"SevLiveMigrationEnabled",
> +                &gMemEncryptGuid,
> +                EFI_VARIABLE_NON_VOLATILE |
> +                EFI_VARIABLE_BOOTSERVICE_ACCESS |
> +                EFI_VARIABLE_RUNTIME_ACCESS,
> +                sizeof (BOOLEAN),
> +                &SevLiveMigrationEnabled
> +               );
> +
> +   DEBUG ((
> +    DEBUG_ERROR,
> +    "%a: Setting SevLiveMigrationEnabled variable, status = %lx\n",

DEBUG_INFO.

Thanks,
Tom

> +    __FUNCTION__,
> +    Status
> +    ));
> +  }
> +}
> diff --git a/OvmfPkg/PlatformDxe/Platform.c b/OvmfPkg/PlatformDxe/Platform.c
> index f2e51960ce..f61302d98b 100644
> --- a/OvmfPkg/PlatformDxe/Platform.c
> +++ b/OvmfPkg/PlatformDxe/Platform.c
> @@ -763,6 +763,11 @@ PlatformInit (
>  {
>    EFI_STATUS Status;
>  
> +  //
> +  // Set Amd Sev configuation
> +  //
> +  AmdSevSetConfig();
> +
>    ExecutePlatformConfig ();
>  
>    mConfigAccess.ExtractConfig = &ExtractConfig;
> diff --git a/OvmfPkg/PlatformDxe/Platform.inf b/OvmfPkg/PlatformDxe/Platform.inf
> index 14727c1220..2896f0a1d1 100644
> --- a/OvmfPkg/PlatformDxe/Platform.inf
> +++ b/OvmfPkg/PlatformDxe/Platform.inf
> @@ -24,6 +24,7 @@
>    PlatformConfig.c
>    PlatformConfig.h
>    PlatformForms.vfr
> +  AmdSev.c
>  
>  [Packages]
>    MdePkg/MdePkg.dec
> @@ -56,6 +57,7 @@
>  [Guids]
>    gEfiIfrTianoGuid
>    gOvmfPlatformConfigGuid
> +  gMemEncryptGuid
>  
>  [Depex]
>    gEfiHiiConfigRoutingProtocolGuid  AND
> diff --git a/OvmfPkg/PlatformDxe/PlatformConfig.h b/OvmfPkg/PlatformDxe/PlatformConfig.h
> index 716514da21..4f662aafa4 100644
> --- a/OvmfPkg/PlatformDxe/PlatformConfig.h
> +++ b/OvmfPkg/PlatformDxe/PlatformConfig.h
> @@ -44,6 +44,11 @@ PlatformConfigLoad (
>    OUT UINT64          *OptionalElements
>    );
>  
> +VOID
> +AmdSevSetConfig(
> +  VOID
> +  );
> +
>  //
>  // Feature flags for OptionalElements.
>  //
>