[mirror_edk2.git] / OvmfPkg / IoMmuDxe / AmdSevIoMmu.c

/** @file

  The protocol provides support to allocate, free, map and umap a DMA buffer
  for bus master (e.g PciHostBridge). When SEV is enabled, the DMA operations
  must be performed on unencrypted buffer hence we use a bounce buffer to map
  the guest buffer into an unencrypted DMA buffer.

  Copyright (c) 2017, AMD Inc. All rights reserved.<BR>
  Copyright (c) 2017, Intel Corporation. All rights reserved.<BR>

  This program and the accompanying materials are licensed and made available
  under the terms and conditions of the BSD License which accompanies this
  distribution.  The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/

#include "AmdSevIoMmu.h"

#define MAP_INFO_SIG SIGNATURE_64 ('M', 'A', 'P', '_', 'I', 'N', 'F', 'O')

typedef struct {
  UINT64                                    Signature;
  LIST_ENTRY                                Link;
  EDKII_IOMMU_OPERATION                     Operation;
  UINTN                                     NumberOfBytes;
  UINTN                                     NumberOfPages;
  EFI_PHYSICAL_ADDRESS                      CryptedAddress;
  EFI_PHYSICAL_ADDRESS                      PlainTextAddress;
} MAP_INFO;

//
// List of MAP_INFO structures recycled by Unmap().
//
// Recycled MAP_INFO structures are equally good for future recycling and
// freeing.
//
STATIC LIST_ENTRY mRecycledMapInfos = INITIALIZE_LIST_HEAD_VARIABLE (
                                        mRecycledMapInfos
                                        );

#define COMMON_BUFFER_SIG SIGNATURE_64 ('C', 'M', 'N', 'B', 'U', 'F', 'F', 'R')

//
// ASCII names for EDKII_IOMMU_OPERATION constants, for debug logging.
//
STATIC CONST CHAR8 * CONST
mBusMasterOperationName[EdkiiIoMmuOperationMaximum] = {
  "Read",
  "Write",
  "CommonBuffer",
  "Read64",
  "Write64",
  "CommonBuffer64"
};

//
// The following structure enables Map() and Unmap() to perform in-place
// decryption and encryption, respectively, for BusMasterCommonBuffer[64]
// operations, without dynamic memory allocation or release.
//
// Both COMMON_BUFFER_HEADER and COMMON_BUFFER_HEADER.StashBuffer are allocated
// by AllocateBuffer() and released by FreeBuffer().
//
#pragma pack (1)
typedef struct {
  UINT64 Signature;

  //
  // Always allocated from EfiBootServicesData type memory, and always
  // encrypted.
  //
  VOID *StashBuffer;

  //
  // Followed by the actual common buffer, starting at the next page.
  //
} COMMON_BUFFER_HEADER;
#pragma pack ()

/**
  Provides the controller-specific addresses required to access system memory
  from a DMA bus master. On SEV guest, the DMA operations must be performed on
  shared buffer hence we allocate a bounce buffer to map the HostAddress to a
  DeviceAddress. The Encryption attribute is removed from the DeviceAddress
  buffer.

  @param  This                  The protocol instance pointer.
  @param  Operation             Indicates if the bus master is going to read or
                                write to system memory.
  @param  HostAddress           The system memory address to map to the PCI
                                controller.
  @param  NumberOfBytes         On input the number of bytes to map. On output
                                the number of bytes that were mapped.
  @param  DeviceAddress         The resulting map address for the bus master
                                PCI controller to use to access the hosts
                                HostAddress.
  @param  Mapping               A resulting value to pass to Unmap().

  @retval EFI_SUCCESS           The range was mapped for the returned
                                NumberOfBytes.
  @retval EFI_UNSUPPORTED       The HostAddress cannot be mapped as a common
                                buffer.
  @retval EFI_INVALID_PARAMETER One or more parameters are invalid.
  @retval EFI_OUT_OF_RESOURCES  The request could not be completed due to a
                                lack of resources.
  @retval EFI_DEVICE_ERROR      The system hardware could not map the requested
                                address.

**/
EFI_STATUS
EFIAPI
IoMmuMap (
  IN     EDKII_IOMMU_PROTOCOL                       *This,
  IN     EDKII_IOMMU_OPERATION                      Operation,
  IN     VOID                                       *HostAddress,
  IN OUT UINTN                                      *NumberOfBytes,
  OUT    EFI_PHYSICAL_ADDRESS                       *DeviceAddress,
  OUT    VOID                                       **Mapping
  )
{
  EFI_STATUS                                        Status;
  LIST_ENTRY                                        *RecycledMapInfo;
  MAP_INFO                                          *MapInfo;
  EFI_ALLOCATE_TYPE                                 AllocateType;
  COMMON_BUFFER_HEADER                              *CommonBufferHeader;
  VOID                                              *DecryptionSource;

  DEBUG ((
    DEBUG_VERBOSE,
    "%a: Operation=%a Host=0x%p Bytes=0x%Lx\n",
    __FUNCTION__,
    ((Operation >= 0 &&
      Operation < ARRAY_SIZE (mBusMasterOperationName)) ?
     mBusMasterOperationName[Operation] :
     "Invalid"),
    HostAddress,
    (UINT64)((NumberOfBytes == NULL) ? 0 : *NumberOfBytes)
    ));

  if (HostAddress == NULL || NumberOfBytes == NULL || DeviceAddress == NULL ||
      Mapping == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // Allocate a MAP_INFO structure to remember the mapping when Unmap() is
  // called later.
  //
  RecycledMapInfo = GetFirstNode (&mRecycledMapInfos);
  if (RecycledMapInfo == &mRecycledMapInfos) {
    //
    // No recycled MAP_INFO structure, allocate a new one.
    //
    MapInfo = AllocatePool (sizeof (MAP_INFO));
    if (MapInfo == NULL) {
      Status = EFI_OUT_OF_RESOURCES;
      goto Failed;
    }
  } else {
    MapInfo = CR (RecycledMapInfo, MAP_INFO, Link, MAP_INFO_SIG);
    RemoveEntryList (RecycledMapInfo);
  }

  //
  // Initialize the MAP_INFO structure, except the PlainTextAddress field
  //
  ZeroMem (&MapInfo->Link, sizeof MapInfo->Link);
  MapInfo->Signature         = MAP_INFO_SIG;
  MapInfo->Operation         = Operation;
  MapInfo->NumberOfBytes     = *NumberOfBytes;
  MapInfo->NumberOfPages     = EFI_SIZE_TO_PAGES (MapInfo->NumberOfBytes);
  MapInfo->CryptedAddress    = (UINTN)HostAddress;

  //
  // In the switch statement below, we point "MapInfo->PlainTextAddress" to the
  // plaintext buffer, according to Operation. We also set "DecryptionSource".
  //
  MapInfo->PlainTextAddress = MAX_ADDRESS;
  AllocateType = AllocateAnyPages;
  DecryptionSource = (VOID *)(UINTN)MapInfo->CryptedAddress;
  switch (Operation) {
  //
  // For BusMasterRead[64] and BusMasterWrite[64] operations, a bounce buffer
  // is necessary regardless of whether the original (crypted) buffer crosses
  // the 4GB limit or not -- we have to allocate a separate plaintext buffer.
  // The only variable is whether the plaintext buffer should be under 4GB.
  //
  case EdkiiIoMmuOperationBusMasterRead:
  case EdkiiIoMmuOperationBusMasterWrite:
    MapInfo->PlainTextAddress = BASE_4GB - 1;
    AllocateType = AllocateMaxAddress;
    //
    // fall through
    //
  case EdkiiIoMmuOperationBusMasterRead64:
  case EdkiiIoMmuOperationBusMasterWrite64:
    //
    // Allocate the implicit plaintext bounce buffer.
    //
    Status = gBS->AllocatePages (
                    AllocateType,
                    EfiBootServicesData,
                    MapInfo->NumberOfPages,
                    &MapInfo->PlainTextAddress
                    );
    if (EFI_ERROR (Status)) {
      goto FreeMapInfo;
    }
    break;

  //
  // For BusMasterCommonBuffer[64] operations, a to-be-plaintext buffer and a
  // stash buffer (for in-place decryption) have been allocated already, with
  // AllocateBuffer(). We only check whether the address of the to-be-plaintext
  // buffer is low enough for the requested operation.
  //
  case EdkiiIoMmuOperationBusMasterCommonBuffer:
    if ((MapInfo->CryptedAddress > BASE_4GB) ||
        (EFI_PAGES_TO_SIZE (MapInfo->NumberOfPages) >
         BASE_4GB - MapInfo->CryptedAddress)) {
      //
      // CommonBuffer operations cannot be remapped. If the common buffer is
      // above 4GB, then it is not possible to generate a mapping, so return an
      // error.
      //
      Status = EFI_UNSUPPORTED;
      goto FreeMapInfo;
    }
    //
    // fall through
    //
  case EdkiiIoMmuOperationBusMasterCommonBuffer64:
    //
    // The buffer at MapInfo->CryptedAddress comes from AllocateBuffer().
    //
    MapInfo->PlainTextAddress = MapInfo->CryptedAddress;
    //
    // Stash the crypted data.
    //
    CommonBufferHeader = (COMMON_BUFFER_HEADER *)(
                           (UINTN)MapInfo->CryptedAddress - EFI_PAGE_SIZE
                           );
    ASSERT (CommonBufferHeader->Signature == COMMON_BUFFER_SIG);
    CopyMem (
      CommonBufferHeader->StashBuffer,
      (VOID *)(UINTN)MapInfo->CryptedAddress,
      MapInfo->NumberOfBytes
      );
    //
    // Point "DecryptionSource" to the stash buffer so that we decrypt
    // it to the original location, after the switch statement.
    //
    DecryptionSource = CommonBufferHeader->StashBuffer;
    break;

  default:
    //
    // Operation is invalid
    //
    Status = EFI_INVALID_PARAMETER;
    goto FreeMapInfo;
  }

  //
  // Clear the memory encryption mask on the plaintext buffer.
  //
  Status = MemEncryptSevClearPageEncMask (
             0,
             MapInfo->PlainTextAddress,
             MapInfo->NumberOfPages,
             TRUE
             );
  ASSERT_EFI_ERROR (Status);
  if (EFI_ERROR (Status)) {
    CpuDeadLoop ();
  }

  //
  // If this is a read operation from the Bus Master's point of view,
  // then copy the contents of the real buffer into the mapped buffer
  // so the Bus Master can read the contents of the real buffer.
  //
  // For BusMasterCommonBuffer[64] operations, the CopyMem() below will decrypt
  // the original data (from the stash buffer) back to the original location.
  //
  if (Operation == EdkiiIoMmuOperationBusMasterRead ||
      Operation == EdkiiIoMmuOperationBusMasterRead64 ||
      Operation == EdkiiIoMmuOperationBusMasterCommonBuffer ||
      Operation == EdkiiIoMmuOperationBusMasterCommonBuffer64) {
    CopyMem (
      (VOID *) (UINTN) MapInfo->PlainTextAddress,
      DecryptionSource,
      MapInfo->NumberOfBytes
      );
  }

  //
  // Populate output parameters.
  //
  *DeviceAddress = MapInfo->PlainTextAddress;
  *Mapping       = MapInfo;

  DEBUG ((
    DEBUG_VERBOSE,
    "%a: Mapping=0x%p Device(PlainText)=0x%Lx Crypted=0x%Lx Pages=0x%Lx\n",
    __FUNCTION__,
    MapInfo,
    MapInfo->PlainTextAddress,
    MapInfo->CryptedAddress,
    (UINT64)MapInfo->NumberOfPages
    ));

  return EFI_SUCCESS;

FreeMapInfo:
  FreePool (MapInfo);

Failed:
  *NumberOfBytes = 0;
  return Status;
}

/**
  Completes the Map() operation and releases any corresponding resources.

  @param  This                  The protocol instance pointer.
  @param  Mapping               The mapping value returned from Map().

  @retval EFI_SUCCESS           The range was unmapped.
  @retval EFI_INVALID_PARAMETER Mapping is not a value that was returned by
                                Map().
  @retval EFI_DEVICE_ERROR      The data was not committed to the target system
                                memory.
**/
EFI_STATUS
EFIAPI
IoMmuUnmap (
  IN  EDKII_IOMMU_PROTOCOL                     *This,
  IN  VOID                                     *Mapping
  )
{
  MAP_INFO                 *MapInfo;
  EFI_STATUS               Status;
  COMMON_BUFFER_HEADER     *CommonBufferHeader;
  VOID                     *EncryptionTarget;

  DEBUG ((DEBUG_VERBOSE, "%a: Mapping=0x%p\n", __FUNCTION__, Mapping));

  if (Mapping == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  MapInfo = (MAP_INFO *)Mapping;

  //
  // set CommonBufferHeader to suppress incorrect compiler/analyzer warnings
  //
  CommonBufferHeader = NULL;

  //
  // For BusMasterWrite[64] operations and BusMasterCommonBuffer[64] operations
  // we have to encrypt the results, ultimately to the original place (i.e.,
  // "MapInfo->CryptedAddress").
  //
  // For BusMasterCommonBuffer[64] operations however, this encryption has to
  // land in-place, so divert the encryption to the stash buffer first.
  //
  EncryptionTarget = (VOID *)(UINTN)MapInfo->CryptedAddress;

  switch (MapInfo->Operation) {
  case EdkiiIoMmuOperationBusMasterCommonBuffer:
  case EdkiiIoMmuOperationBusMasterCommonBuffer64:
    ASSERT (MapInfo->PlainTextAddress == MapInfo->CryptedAddress);

    CommonBufferHeader = (COMMON_BUFFER_HEADER *)(
                           (UINTN)MapInfo->PlainTextAddress - EFI_PAGE_SIZE
                           );
    ASSERT (CommonBufferHeader->Signature == COMMON_BUFFER_SIG);
    EncryptionTarget = CommonBufferHeader->StashBuffer;
    //
    // fall through
    //

  case EdkiiIoMmuOperationBusMasterWrite:
  case EdkiiIoMmuOperationBusMasterWrite64:
    CopyMem (
      EncryptionTarget,
      (VOID *) (UINTN) MapInfo->PlainTextAddress,
      MapInfo->NumberOfBytes
      );
    break;

  default:
    //
    // nothing to encrypt after BusMasterRead[64] operations
    //
    break;
  }

  //
  // Restore the memory encryption mask on the area we used to hold the
  // plaintext.
  //
  Status = MemEncryptSevSetPageEncMask (
             0,
             MapInfo->PlainTextAddress,
             MapInfo->NumberOfPages,
             TRUE
             );
  ASSERT_EFI_ERROR (Status);
  if (EFI_ERROR (Status)) {
    CpuDeadLoop ();
  }

  //
  // For BusMasterCommonBuffer[64] operations, copy the stashed data to the
  // original (now encrypted) location.
  //
  // For all other operations, fill the late bounce buffer (which existed as
  // plaintext at some point) with zeros, and then release it.
  //
  if (MapInfo->Operation == EdkiiIoMmuOperationBusMasterCommonBuffer ||
      MapInfo->Operation == EdkiiIoMmuOperationBusMasterCommonBuffer64) {
    CopyMem (
      (VOID *)(UINTN)MapInfo->CryptedAddress,
      CommonBufferHeader->StashBuffer,
      MapInfo->NumberOfBytes
      );

    //
    // Recycle the MAP_INFO structure.
    //
    InsertTailList (&mRecycledMapInfos, &MapInfo->Link);
  } else {
    ZeroMem (
      (VOID *)(UINTN)MapInfo->PlainTextAddress,
      EFI_PAGES_TO_SIZE (MapInfo->NumberOfPages)
      );
    gBS->FreePages (MapInfo->PlainTextAddress, MapInfo->NumberOfPages);

    //
    // Free the MAP_INFO structure.
    //
    FreePool (MapInfo);
  }

  return EFI_SUCCESS;
}

/**
  Allocates pages that are suitable for an OperationBusMasterCommonBuffer or
  OperationBusMasterCommonBuffer64 mapping.

  @param  This                  The protocol instance pointer.
  @param  Type                  This parameter is not used and must be ignored.
  @param  MemoryType            The type of memory to allocate,
                                EfiBootServicesData or EfiRuntimeServicesData.
  @param  Pages                 The number of pages to allocate.
  @param  HostAddress           A pointer to store the base system memory
                                address of the allocated range.
  @param  Attributes            The requested bit mask of attributes for the
                                allocated range.

  @retval EFI_SUCCESS           The requested memory pages were allocated.
  @retval EFI_UNSUPPORTED       Attributes is unsupported. The only legal
                                attribute bits are MEMORY_WRITE_COMBINE and
                                MEMORY_CACHED.
  @retval EFI_INVALID_PARAMETER One or more parameters are invalid.
  @retval EFI_OUT_OF_RESOURCES  The memory pages could not be allocated.

**/
EFI_STATUS
EFIAPI
IoMmuAllocateBuffer (
  IN     EDKII_IOMMU_PROTOCOL                     *This,
  IN     EFI_ALLOCATE_TYPE                        Type,
  IN     EFI_MEMORY_TYPE                          MemoryType,
  IN     UINTN                                    Pages,
  IN OUT VOID                                     **HostAddress,
  IN     UINT64                                   Attributes
  )
{
  EFI_STATUS                Status;
  EFI_PHYSICAL_ADDRESS      PhysicalAddress;
  VOID                      *StashBuffer;
  UINTN                     CommonBufferPages;
  COMMON_BUFFER_HEADER      *CommonBufferHeader;

  DEBUG ((
    DEBUG_VERBOSE,
    "%a: MemoryType=%u Pages=0x%Lx Attributes=0x%Lx\n",
    __FUNCTION__,
    (UINT32)MemoryType,
    (UINT64)Pages,
    Attributes
    ));

  //
  // Validate Attributes
  //
  if ((Attributes & EDKII_IOMMU_ATTRIBUTE_INVALID_FOR_ALLOCATE_BUFFER) != 0) {
    return EFI_UNSUPPORTED;
  }

  //
  // Check for invalid inputs
  //
  if (HostAddress == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // The only valid memory types are EfiBootServicesData and
  // EfiRuntimeServicesData
  //
  if (MemoryType != EfiBootServicesData &&
      MemoryType != EfiRuntimeServicesData) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // We'll need a header page for the COMMON_BUFFER_HEADER structure.
  //
  if (Pages > MAX_UINTN - 1) {
    return EFI_OUT_OF_RESOURCES;
  }
  CommonBufferPages = Pages + 1;

  //
  // Allocate the stash in EfiBootServicesData type memory.
  //
  // Map() will temporarily save encrypted data in the stash for
  // BusMasterCommonBuffer[64] operations, so the data can be decrypted to the
  // original location.
  //
  // Unmap() will temporarily save plaintext data in the stash for
  // BusMasterCommonBuffer[64] operations, so the data can be encrypted to the
  // original location.
  //
  // StashBuffer always resides in encrypted memory.
  //
  StashBuffer = AllocatePages (Pages);
  if (StashBuffer == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  PhysicalAddress = (UINTN)-1;
  if ((Attributes & EDKII_IOMMU_ATTRIBUTE_DUAL_ADDRESS_CYCLE) == 0) {
    //
    // Limit allocations to memory below 4GB
    //
    PhysicalAddress = SIZE_4GB - 1;
  }
  Status = gBS->AllocatePages (
                  AllocateMaxAddress,
                  MemoryType,
                  CommonBufferPages,
                  &PhysicalAddress
                  );
  if (EFI_ERROR (Status)) {
    goto FreeStashBuffer;
  }

  CommonBufferHeader = (VOID *)(UINTN)PhysicalAddress;
  PhysicalAddress += EFI_PAGE_SIZE;

  CommonBufferHeader->Signature = COMMON_BUFFER_SIG;
  CommonBufferHeader->StashBuffer = StashBuffer;

  *HostAddress = (VOID *)(UINTN)PhysicalAddress;

  DEBUG ((
    DEBUG_VERBOSE,
    "%a: Host=0x%Lx Stash=0x%p\n",
    __FUNCTION__,
    PhysicalAddress,
    StashBuffer
    ));
  return EFI_SUCCESS;

FreeStashBuffer:
  FreePages (StashBuffer, Pages);
  return Status;
}

/**
  Frees memory that was allocated with AllocateBuffer().

  @param  This                  The protocol instance pointer.
  @param  Pages                 The number of pages to free.
  @param  HostAddress           The base system memory address of the allocated
                                range.

  @retval EFI_SUCCESS           The requested memory pages were freed.
  @retval EFI_INVALID_PARAMETER The memory range specified by HostAddress and
                                Pages was not allocated with AllocateBuffer().

**/
EFI_STATUS
EFIAPI
IoMmuFreeBuffer (
  IN  EDKII_IOMMU_PROTOCOL                     *This,
  IN  UINTN                                    Pages,
  IN  VOID                                     *HostAddress
  )
{
  UINTN                CommonBufferPages;
  COMMON_BUFFER_HEADER *CommonBufferHeader;

  DEBUG ((
    DEBUG_VERBOSE,
    "%a: Host=0x%p Pages=0x%Lx\n",
    __FUNCTION__,
    HostAddress,
    (UINT64)Pages
    ));

  CommonBufferPages = Pages + 1;
  CommonBufferHeader = (COMMON_BUFFER_HEADER *)(
                         (UINTN)HostAddress - EFI_PAGE_SIZE
                         );

  //
  // Check the signature.
  //
  ASSERT (CommonBufferHeader->Signature == COMMON_BUFFER_SIG);
  if (CommonBufferHeader->Signature != COMMON_BUFFER_SIG) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // Free the stash buffer. This buffer was always encrypted, so no need to
  // zero it.
  //
  FreePages (CommonBufferHeader->StashBuffer, Pages);

  //
  // Release the common buffer itself. Unmap() has re-encrypted it in-place, so
  // no need to zero it.
  //
  return gBS->FreePages ((UINTN)CommonBufferHeader, CommonBufferPages);
}


/**
  Set IOMMU attribute for a system memory.

  If the IOMMU protocol exists, the system memory cannot be used
  for DMA by default.

  When a device requests a DMA access for a system memory,
  the device driver need use SetAttribute() to update the IOMMU
  attribute to request DMA access (read and/or write).

  The DeviceHandle is used to identify which device submits the request.
  The IOMMU implementation need translate the device path to an IOMMU device
  ID, and set IOMMU hardware register accordingly.
  1) DeviceHandle can be a standard PCI device.
     The memory for BusMasterRead need set EDKII_IOMMU_ACCESS_READ.
     The memory for BusMasterWrite need set EDKII_IOMMU_ACCESS_WRITE.
     The memory for BusMasterCommonBuffer need set
     EDKII_IOMMU_ACCESS_READ|EDKII_IOMMU_ACCESS_WRITE.
     After the memory is used, the memory need set 0 to keep it being
     protected.
  2) DeviceHandle can be an ACPI device (ISA, I2C, SPI, etc).
     The memory for DMA access need set EDKII_IOMMU_ACCESS_READ and/or
     EDKII_IOMMU_ACCESS_WRITE.

  @param[in]  This              The protocol instance pointer.
  @param[in]  DeviceHandle      The device who initiates the DMA access
                                request.
  @param[in]  Mapping           The mapping value returned from Map().
  @param[in]  IoMmuAccess       The IOMMU access.

  @retval EFI_SUCCESS            The IoMmuAccess is set for the memory range
                                 specified by DeviceAddress and Length.
  @retval EFI_INVALID_PARAMETER  DeviceHandle is an invalid handle.
  @retval EFI_INVALID_PARAMETER  Mapping is not a value that was returned by
                                 Map().
  @retval EFI_INVALID_PARAMETER  IoMmuAccess specified an illegal combination
                                 of access.
  @retval EFI_UNSUPPORTED        DeviceHandle is unknown by the IOMMU.
  @retval EFI_UNSUPPORTED        The bit mask of IoMmuAccess is not supported
                                 by the IOMMU.
  @retval EFI_UNSUPPORTED        The IOMMU does not support the memory range
                                 specified by Mapping.
  @retval EFI_OUT_OF_RESOURCES   There are not enough resources available to
                                 modify the IOMMU access.
  @retval EFI_DEVICE_ERROR       The IOMMU device reported an error while
                                 attempting the operation.

**/
EFI_STATUS
EFIAPI
IoMmuSetAttribute (
  IN EDKII_IOMMU_PROTOCOL  *This,
  IN EFI_HANDLE            DeviceHandle,
  IN VOID                  *Mapping,
  IN UINT64                IoMmuAccess
  )
{
  return EFI_UNSUPPORTED;
}

EDKII_IOMMU_PROTOCOL  mAmdSev = {
  EDKII_IOMMU_PROTOCOL_REVISION,
  IoMmuSetAttribute,
  IoMmuMap,
  IoMmuUnmap,
  IoMmuAllocateBuffer,
  IoMmuFreeBuffer,
};

/**
  Initialize Iommu Protocol.

**/
EFI_STATUS
EFIAPI
AmdSevInstallIoMmuProtocol (
  VOID
  )
{
  EFI_STATUS  Status;
  EFI_HANDLE  Handle;

  Handle = NULL;
  Status = gBS->InstallMultipleProtocolInterfaces (
                  &Handle,
                  &gEdkiiIoMmuProtocolGuid, &mAmdSev,
                  NULL
                  );
  return Status;
}