Re: [PATCH V1 1/3] OvmfPkg/IoMmuDxe: Reserve shared memory region for DMA operation

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

On 12/5/22 02:08, Min Xu wrote:
> From: Min M Xu <min.m.xu@intel.com>
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4171
> 
> A typical QEMU fw_cfg read bytes with IOMMU for td guest is that:
> (QemuFwCfgReadBytes@QemuFwCfgLib.c is the example)
> 1) Allocate DMA Access buffer
> 2) Map actual data buffer
> 3) start the transfer and wait for the transfer to complete
> 4) Free DMA Access buffer
> 5) Un-map actual data buffer
> 
> In step 1/2, Private memories are allocated, converted to shared memories.
> In Step 4/5 the shared memories are converted to private memories and
> accepted again. The final step is to free the pages.
> 
> This is time-consuming and impacts td guest's boot perf (both direct boot
> and grub boot) badly.
> 
> In a typical grub boot, there are about 5000 calls of page allocation and
> private/share conversion. Most of page size is less than 32KB.
> 
> This patch allocates a memory region and initializes it into pieces of
> memory with different sizes. A piece of such memory consists of 2 parts:
> the first page is of private memory, and the other pages are shared
> memory. This is to meet the layout of common buffer.
> 
> When allocating bounce buffer in IoMmuMap(), IoMmuAllocateBounceBuffer()
> is called to allocate the buffer. Accordingly when freeing bounce buffer
> in IoMmuUnmapWorker(), IoMmuFreeBounceBuffer() is called to free the
> bounce buffer. CommonBuffer is allocated by IoMmuAllocateCommonBuffer
> and accordingly freed by IoMmuFreeCommonBuffer.
> 
> This feature is tested in Intel TDX pre-production platform. It saves up
> to hundreds of ms in a grub boot.

This crashes SEV guests. I presume because the call to
IoMmuReleaseReservedSharedMem() is not bracketed by a check for TDX.

I plan to add support for SEV, which would avoid the crash, not sure if
you want to integrate it into a single series or not. Here's the patch I
was looking to add that should be pretty easy to integrate. Let me know if
you would like to integrate it in your series or just have me submit it as
a reply to your series:


OvmfPkg/IoMmuDxe: Add SEV support for reserved shared memory

From: Tom Lendacky <thomas.lendacky@amd.com>

Add support to use the reserved shared memory within the IoMmu library.
This improves boot times for all SEV guests, with SEV-SNP benefiting the
most as it avoids the page state change call to the hypervisor.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
  OvmfPkg/IoMmuDxe/CcIoMmu.c     |   82 ++++++++++++++++++++--------------------
  OvmfPkg/IoMmuDxe/IoMmuBuffer.c |   54 ++++++++++++++++++++------
  2 files changed, 83 insertions(+), 53 deletions(-)

diff --git a/OvmfPkg/IoMmuDxe/CcIoMmu.c b/OvmfPkg/IoMmuDxe/CcIoMmu.c
index 1479af469881..7c2843cd238a 100644
--- a/OvmfPkg/IoMmuDxe/CcIoMmu.c
+++ b/OvmfPkg/IoMmuDxe/CcIoMmu.c
@@ -223,30 +223,32 @@ IoMmuMap (
        goto FreeMapInfo;
    }
  
-  if (CC_GUEST_IS_SEV (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+  if (MapInfo->ReservedMemBitmap == 0) {
      //
-    // Clear the memory encryption mask on the plaintext buffer.
-    //
-    Status = MemEncryptSevClearPageEncMask (
-               0,
-               MapInfo->PlainTextAddress,
-               MapInfo->NumberOfPages
-               );
-  } else if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
-    //
-    // Set the memory shared bit.
      // If MapInfo->ReservedMemBitmap is 0, it means the bounce buffer is not allocated
      // from the pre-allocated shared memory, so it must be converted to shared memory here.
      //
-    if (MapInfo->ReservedMemBitmap == 0) {
+    if (CC_GUEST_IS_SEV (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+      //
+      // Clear the memory encryption mask on the plaintext buffer.
+      //
+      Status = MemEncryptSevClearPageEncMask (
+                 0,
+                 MapInfo->PlainTextAddress,
+                 MapInfo->NumberOfPages
+                 );
+    } else if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+      //
+      // Set the memory shared bit.
+      //
        Status = MemEncryptTdxSetPageSharedBit (
                   0,
                   MapInfo->PlainTextAddress,
                   MapInfo->NumberOfPages
                   );
+    } else {
+      ASSERT (FALSE);
      }
-  } else {
-    ASSERT (FALSE);
    }
  
    ASSERT_EFI_ERROR (Status);
@@ -396,30 +398,30 @@ IoMmuUnmapWorker (
        break;
    }
  
-  if (CC_GUEST_IS_SEV (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
-    //
-    // Restore the memory encryption mask on the area we used to hold the
-    // plaintext.
-    //
-    Status = MemEncryptSevSetPageEncMask (
-               0,
-               MapInfo->PlainTextAddress,
-               MapInfo->NumberOfPages
-               );
-  } else if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
-    //
-    // Restore the memory shared bit mask on the area we used to hold the
-    // plaintext.
-    //
-    if (MapInfo->ReservedMemBitmap == 0) {
+  if (MapInfo->ReservedMemBitmap == 0) {
+    if (CC_GUEST_IS_SEV (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+      //
+      // Restore the memory encryption mask on the area we used to hold the
+      // plaintext.
+      //
+      Status = MemEncryptSevSetPageEncMask (
+                 0,
+                 MapInfo->PlainTextAddress,
+                 MapInfo->NumberOfPages
+                 );
+    } else if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+      //
+      // Restore the memory shared bit mask on the area we used to hold the
+      // plaintext.
+      //
        Status = MemEncryptTdxClearPageSharedBit (
                   0,
                   MapInfo->PlainTextAddress,
                   MapInfo->NumberOfPages
                   );
+    } else {
+      ASSERT (FALSE);
      }
-  } else {
-    ASSERT (FALSE);
    }
  
    ASSERT_EFI_ERROR (Status);
@@ -924,16 +926,14 @@ InstallIoMmuProtocol (
    }
  
    //
-  // Currently only Tdx guest support Reserved shared memory for DMA operation.
+  // For CC guests, use reserved shared memory for DMA operation.
    //
-  if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
-    mReservedSharedMemSupported = TRUE;
-    Status                      = IoMmuInitReservedSharedMem ();
-    if (EFI_ERROR (Status)) {
-      mReservedSharedMemSupported = FALSE;
-    } else {
-      DEBUG ((DEBUG_INFO, "%a: Feature of reserved memory for DMA is supported.\n", __FUNCTION__));
-    }
+  mReservedSharedMemSupported = TRUE;
+  Status                      = IoMmuInitReservedSharedMem ();
+  if (EFI_ERROR (Status)) {
+    mReservedSharedMemSupported = FALSE;
+  } else {
+    DEBUG ((DEBUG_INFO, "%a: Feature of reserved memory for DMA is supported.\n", __FUNCTION__));
    }
  
    return EFI_SUCCESS;
diff --git a/OvmfPkg/IoMmuDxe/IoMmuBuffer.c b/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
index 5ada8e9d57bd..d69969b6b763 100644
--- a/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
+++ b/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
@@ -9,7 +9,9 @@
  #include <Library/BaseMemoryLib.h>
  #include <Library/DebugLib.h>
  #include <Library/MemoryAllocationLib.h>
+#include <Library/MemEncryptSevLib.h>
  #include <Library/MemEncryptTdxLib.h>
+#include <Library/PcdLib.h>
  #include <Library/UefiBootServicesTableLib.h>
  #include "IoMmuInternal.h"
  
@@ -105,6 +107,7 @@ IoMmuInitReservedSharedMem (
    UINTN                     TotalPages;
    IOMMU_RESERVED_MEM_RANGE  *MemRange;
    EFI_PHYSICAL_ADDRESS      PhysicalAddress;
+  UINT64                    SharedAddress;
  
    if (!mReservedSharedMemSupported) {
      return EFI_UNSUPPORTED;
@@ -129,12 +132,25 @@ IoMmuInitReservedSharedMem (
      MemRange->StartAddressOfMemRange = PhysicalAddress;
  
      for (Index2 = 0; Index2 < MemRange->Slots; Index2++) {
-      Status = MemEncryptTdxSetPageSharedBit (
-                 0,
-                 (UINT64)(UINTN)(MemRange->StartAddressOfMemRange + Index2 * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize),
-                 EFI_SIZE_TO_PAGES (MemRange->DataSize)
-                 );
-      ASSERT (!EFI_ERROR (Status));
+      SharedAddress = (UINT64)(UINTN)(MemRange->StartAddressOfMemRange + Index2 * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize);
+
+      if (CC_GUEST_IS_SEV (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+        Status = MemEncryptSevClearPageEncMask (
+                   0,
+                   SharedAddress,
+                   EFI_SIZE_TO_PAGES (MemRange->DataSize)
+                   );
+        ASSERT (!EFI_ERROR (Status));
+      } else if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+        Status = MemEncryptTdxSetPageSharedBit (
+                   0,
+                   SharedAddress,
+                   EFI_SIZE_TO_PAGES (MemRange->DataSize)
+                   );
+        ASSERT (!EFI_ERROR (Status));
+      } else {
+        ASSERT (FALSE);
+      }
      }
  
      PhysicalAddress += (MemRange->Slots * SIZE_OF_MEM_RANGE (MemRange));
@@ -156,16 +172,30 @@ IoMmuReleaseReservedSharedMem (
    EFI_STATUS                Status;
    UINT32                    Index1, Index2;
    IOMMU_RESERVED_MEM_RANGE  *MemRange;
+  UINT64                    SharedAddress;
  
    for (Index1 = 0; Index1 < ARRAY_SIZE (mReservedMemRanges); Index1++) {
      MemRange = &mReservedMemRanges[Index1];
      for (Index2 = 0; Index2 < MemRange->Slots; Index2++) {
-      Status = MemEncryptTdxClearPageSharedBit (
-                 0,
-                 (UINT64)(UINTN)(MemRange->StartAddressOfMemRange + Index2 * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize),
-                 EFI_SIZE_TO_PAGES (MemRange->DataSize)
-                 );
-      ASSERT (!EFI_ERROR (Status));
+      SharedAddress = (UINT64)(UINTN)(MemRange->StartAddressOfMemRange + Index2 * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize);
+
+      if (CC_GUEST_IS_SEV (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+        Status = MemEncryptSevSetPageEncMask (
+                   0,
+                   SharedAddress,
+                   EFI_SIZE_TO_PAGES (MemRange->DataSize)
+                   );
+        ASSERT (!EFI_ERROR (Status));
+      } else if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
+        Status = MemEncryptTdxClearPageSharedBit (
+                   0,
+                   SharedAddress,
+                   EFI_SIZE_TO_PAGES (MemRange->DataSize)
+                   );
+        ASSERT (!EFI_ERROR (Status));
+      } else {
+        ASSERT (FALSE);
+      }
      }
    }
  

> 
> Cc: Erdem Aktas <erdemaktas@google.com>
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Min Xu <min.m.xu@intel.com>
> ---
>   OvmfPkg/IoMmuDxe/AmdSevIoMmu.c   | 142 +++++------
>   OvmfPkg/IoMmuDxe/IoMmuBuffer.c   | 425 +++++++++++++++++++++++++++++++
>   OvmfPkg/IoMmuDxe/IoMmuDxe.inf    |   1 +
>   OvmfPkg/IoMmuDxe/IoMmuInternal.h | 179 +++++++++++++
>   4 files changed, 676 insertions(+), 71 deletions(-)
>   create mode 100644 OvmfPkg/IoMmuDxe/IoMmuBuffer.c
>   create mode 100644 OvmfPkg/IoMmuDxe/IoMmuInternal.h
> 
> diff --git a/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c b/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c
> index 6b65897f032a..77e46bbf4a60 100644
> --- a/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c
> +++ b/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c
> @@ -15,18 +15,7 @@
>   #include <Library/PcdLib.h>
>   #include <ConfidentialComputingGuestAttr.h>
>   #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;
> +#include "IoMmuInternal.h"
>   
>   //
>   // List of the MAP_INFO structures that have been set up by IoMmuMap() and not
> @@ -35,7 +24,10 @@ typedef struct {
>   //
>   STATIC LIST_ENTRY  mMapInfos = INITIALIZE_LIST_HEAD_VARIABLE (mMapInfos);
>   
> -#define COMMON_BUFFER_SIG  SIGNATURE_64 ('C', 'M', 'N', 'B', 'U', 'F', 'F', 'R')
> +//
> +// Indicate if the feature of reserved memory is supported in DMA operation.
> +//
> +BOOLEAN  mReservedSharedMemSupported = FALSE;
>   
>   //
>   // ASCII names for EDKII_IOMMU_OPERATION constants, for debug logging.
> @@ -50,30 +42,6 @@ mBusMasterOperationName[EdkiiIoMmuOperationMaximum] = {
>     "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/TDX guest, the DMA operations must be performed on
> @@ -139,6 +107,8 @@ IoMmuMap (
>       return EFI_INVALID_PARAMETER;
>     }
>   
> +  Status = EFI_SUCCESS;
> +
>     //
>     // Allocate a MAP_INFO structure to remember the mapping when Unmap() is
>     // called later.
> @@ -153,11 +123,12 @@ IoMmuMap (
>     // 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;
> +  MapInfo->Signature         = MAP_INFO_SIG;
> +  MapInfo->Operation         = Operation;
> +  MapInfo->NumberOfBytes     = *NumberOfBytes;
> +  MapInfo->NumberOfPages     = EFI_SIZE_TO_PAGES (MapInfo->NumberOfBytes);
> +  MapInfo->CryptedAddress    = (UINTN)HostAddress;
> +  MapInfo->ReservedMemBitmap = 0;
>   
>     //
>     // In the switch statement below, we point "MapInfo->PlainTextAddress" to the
> @@ -185,12 +156,11 @@ IoMmuMap (
>         //
>         // Allocate the implicit plaintext bounce buffer.
>         //
> -      Status = gBS->AllocatePages (
> -                      AllocateType,
> -                      EfiBootServicesData,
> -                      MapInfo->NumberOfPages,
> -                      &MapInfo->PlainTextAddress
> -                      );
> +      Status = IoMmuAllocateBounceBuffer (
> +                 AllocateType,
> +                 EfiBootServicesData,
> +                 MapInfo
> +                 );
>         if (EFI_ERROR (Status)) {
>           goto FreeMapInfo;
>         }
> @@ -241,7 +211,8 @@ IoMmuMap (
>         // Point "DecryptionSource" to the stash buffer so that we decrypt
>         // it to the original location, after the switch statement.
>         //
> -      DecryptionSource = CommonBufferHeader->StashBuffer;
> +      DecryptionSource           = CommonBufferHeader->StashBuffer;
> +      MapInfo->ReservedMemBitmap = CommonBufferHeader->ReservedMemBitmap;
>         break;
>   
>       default:
> @@ -264,12 +235,16 @@ IoMmuMap (
>     } else if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
>       //
>       // Set the memory shared bit.
> +    // If MapInfo->ReservedMemBitmap is 0, it means the bounce buffer is not allocated
> +    // from the pre-allocated shared memory, so it must be converted to shared memory here.
>       //
> -    Status = MemEncryptTdxSetPageSharedBit (
> -               0,
> -               MapInfo->PlainTextAddress,
> -               MapInfo->NumberOfPages
> -               );
> +    if (MapInfo->ReservedMemBitmap == 0) {
> +      Status = MemEncryptTdxSetPageSharedBit (
> +                 0,
> +                 MapInfo->PlainTextAddress,
> +                 MapInfo->NumberOfPages
> +                 );
> +    }
>     } else {
>       ASSERT (FALSE);
>     }
> @@ -311,12 +286,13 @@ IoMmuMap (
>   
>     DEBUG ((
>       DEBUG_VERBOSE,
> -    "%a: Mapping=0x%p Device(PlainText)=0x%Lx Crypted=0x%Lx Pages=0x%Lx\n",
> +    "%a: Mapping=0x%p Device(PlainText)=0x%Lx Crypted=0x%Lx Pages=0x%Lx, ReservedMemBitmap=0x%Lx\n",
>       __FUNCTION__,
>       MapInfo,
>       MapInfo->PlainTextAddress,
>       MapInfo->CryptedAddress,
> -    (UINT64)MapInfo->NumberOfPages
> +    (UINT64)MapInfo->NumberOfPages,
> +    MapInfo->ReservedMemBitmap
>       ));
>   
>     return EFI_SUCCESS;
> @@ -435,11 +411,13 @@ IoMmuUnmapWorker (
>       // Restore the memory shared bit mask on the area we used to hold the
>       // plaintext.
>       //
> -    Status = MemEncryptTdxClearPageSharedBit (
> -               0,
> -               MapInfo->PlainTextAddress,
> -               MapInfo->NumberOfPages
> -               );
> +    if (MapInfo->ReservedMemBitmap == 0) {
> +      Status = MemEncryptTdxClearPageSharedBit (
> +                 0,
> +                 MapInfo->PlainTextAddress,
> +                 MapInfo->NumberOfPages
> +                 );
> +    }
>     } else {
>       ASSERT (FALSE);
>     }
> @@ -470,8 +448,9 @@ IoMmuUnmapWorker (
>         (VOID *)(UINTN)MapInfo->PlainTextAddress,
>         EFI_PAGES_TO_SIZE (MapInfo->NumberOfPages)
>         );
> +
>       if (!MemoryMapLocked) {
> -      gBS->FreePages (MapInfo->PlainTextAddress, MapInfo->NumberOfPages);
> +      IoMmuFreeBounceBuffer (MapInfo);
>       }
>     }
>   
> @@ -551,6 +530,7 @@ IoMmuAllocateBuffer (
>     VOID                  *StashBuffer;
>     UINTN                 CommonBufferPages;
>     COMMON_BUFFER_HEADER  *CommonBufferHeader;
> +  UINT32                ReservedMemBitmap;
>   
>     DEBUG ((
>       DEBUG_VERBOSE,
> @@ -620,12 +600,13 @@ IoMmuAllocateBuffer (
>       PhysicalAddress = SIZE_4GB - 1;
>     }
>   
> -  Status = gBS->AllocatePages (
> -                  AllocateMaxAddress,
> -                  MemoryType,
> -                  CommonBufferPages,
> -                  &PhysicalAddress
> -                  );
> +  Status = IoMmuAllocateCommonBuffer (
> +             MemoryType,
> +             CommonBufferPages,
> +             &PhysicalAddress,
> +             &ReservedMemBitmap
> +             );
> +
>     if (EFI_ERROR (Status)) {
>       goto FreeStashBuffer;
>     }
> @@ -633,8 +614,9 @@ IoMmuAllocateBuffer (
>     CommonBufferHeader = (VOID *)(UINTN)PhysicalAddress;
>     PhysicalAddress   += EFI_PAGE_SIZE;
>   
> -  CommonBufferHeader->Signature   = COMMON_BUFFER_SIG;
> -  CommonBufferHeader->StashBuffer = StashBuffer;
> +  CommonBufferHeader->Signature         = COMMON_BUFFER_SIG;
> +  CommonBufferHeader->StashBuffer       = StashBuffer;
> +  CommonBufferHeader->ReservedMemBitmap = ReservedMemBitmap;
>   
>     *HostAddress = (VOID *)(UINTN)PhysicalAddress;
>   
> @@ -707,7 +689,7 @@ IoMmuFreeBuffer (
>     // Release the common buffer itself. Unmap() has re-encrypted it in-place, so
>     // no need to zero it.
>     //
> -  return gBS->FreePages ((UINTN)CommonBufferHeader, CommonBufferPages);
> +  return IoMmuFreeCommonBuffer (CommonBufferHeader, CommonBufferPages);
>   }
>   
>   /**
> @@ -878,6 +860,11 @@ IoMmuUnmapAllMappings (
>         TRUE      // MemoryMapLocked
>         );
>     }
> +
> +  //
> +  // Release the reserved shared memory as well.
> +  //
> +  IoMmuReleaseReservedSharedMem (TRUE);
>   }
>   
>   /**
> @@ -936,6 +923,19 @@ InstallIoMmuProtocol (
>       goto CloseExitBootEvent;
>     }
>   
> +  //
> +  // Currently only Tdx guest support Reserved shared memory for DMA operation.
> +  //
> +  if (CC_GUEST_IS_TDX (PcdGet64 (PcdConfidentialComputingGuestAttr))) {
> +    mReservedSharedMemSupported = TRUE;
> +    Status                      = IoMmuInitReservedSharedMem ();
> +    if (EFI_ERROR (Status)) {
> +      mReservedSharedMemSupported = FALSE;
> +    } else {
> +      DEBUG ((DEBUG_INFO, "%a: Feature of reserved memory for DMA is supported.\n", __FUNCTION__));
> +    }
> +  }
> +
>     return EFI_SUCCESS;
>   
>   CloseExitBootEvent:
> diff --git a/OvmfPkg/IoMmuDxe/IoMmuBuffer.c b/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
> new file mode 100644
> index 000000000000..5ada8e9d57bd
> --- /dev/null
> +++ b/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
> @@ -0,0 +1,425 @@
> +/** @file
> +
> +  Copyright (c) 2022, Intel Corporation. All rights reserved.<BR>
> +
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +#include <Library/BaseLib.h>
> +#include <Library/BaseMemoryLib.h>
> +#include <Library/DebugLib.h>
> +#include <Library/MemoryAllocationLib.h>
> +#include <Library/MemEncryptTdxLib.h>
> +#include <Library/UefiBootServicesTableLib.h>
> +#include "IoMmuInternal.h"
> +
> +extern BOOLEAN  mReservedSharedMemSupported;
> +
> +#define SIZE_OF_MEM_RANGE(MemRange)  (MemRange->HeaderSize + MemRange->DataSize)
> +
> +#define RESERVED_MEM_BITMAP_4K_MASK    0xf
> +#define RESERVED_MEM_BITMAP_32K_MASK   0xff0
> +#define RESERVED_MEM_BITMAP_128K_MASK  0x3000
> +#define RESERVED_MEM_BITMAP_1M_MASK    0x40000
> +#define RESERVED_MEM_BITMAP_2M_MASK    0x180000
> +#define RESERVED_MEM_BITMAP_MASK       0x1fffff
> +
> +STATIC IOMMU_RESERVED_MEM_RANGE  mReservedMemRanges[] = {
> +  { RESERVED_MEM_BITMAP_4K_MASK,   0,  4, SIZE_4KB,   SIZE_4KB, 0 },
> +  { RESERVED_MEM_BITMAP_32K_MASK,  4,  8, SIZE_32KB,  SIZE_4KB, 0 },
> +  { RESERVED_MEM_BITMAP_128K_MASK, 12, 2, SIZE_128KB, SIZE_4KB, 0 },
> +  { RESERVED_MEM_BITMAP_1M_MASK,   14, 1, SIZE_1MB,   SIZE_4KB, 0 },
> +  { RESERVED_MEM_BITMAP_2M_MASK,   15, 2, SIZE_2MB,   SIZE_4KB, 0 },
> +};
> +
> +//
> +// Bitmap of the allocation of reserved memory.
> +//
> +STATIC UINT32  mReservedMemBitmap = 0;
> +
> +//
> +// Start address of the reserved memory region.
> +//
> +STATIC EFI_PHYSICAL_ADDRESS  mReservedSharedMemAddress = 0;
> +
> +//
> +// Total size of the reserved memory region.
> +//
> +STATIC UINT32  mReservedSharedMemSize = 0;
> +
> +/**
> + * Calculate the size of reserved memory.
> + *
> + * @retval UINT32   Size of the reserved memory
> + */
> +STATIC
> +UINT32
> +CalcuateReservedMemSize (
> +  VOID
> +  )
> +{
> +  UINT32                    Index;
> +  IOMMU_RESERVED_MEM_RANGE  *MemRange;
> +
> +  if (mReservedSharedMemSize != 0) {
> +    return mReservedSharedMemSize;
> +  }
> +
> +  for (Index = 0; Index < ARRAY_SIZE (mReservedMemRanges); Index++) {
> +    MemRange                = &mReservedMemRanges[Index];
> +    mReservedSharedMemSize += (SIZE_OF_MEM_RANGE (MemRange) * MemRange->Slots);
> +  }
> +
> +  return mReservedSharedMemSize;
> +}
> +
> +/**
> + * Allocate a memory region and convert it to be shared. This memory region will be
> + * used in the DMA operation.
> + *
> + * The pre-alloc memory contains pieces of memory regions with different size. The
> + * allocation of the shared memory regions are indicated by a 32-bit bitmap (mReservedMemBitmap).
> + *
> + * The memory regions are consumed by IoMmuAllocateBuffer (in which CommonBuffer is allocated) and
> + * IoMmuMap (in which bounce buffer is allocated).
> + *
> + * The CommonBuffer contains 2 parts, one page for CommonBufferHeader which is private memory,
> + * the other part is shared memory. So the layout of a piece of memory region after initialization
> + * looks like:
> + *
> + *     |------------|----------------------------|
> + *     | Header     |    Data                    |  <-- a piece of pre-alloc memory region
> + *     | 4k, private| 4k/32k/128k/etc, shared    |
> + *     |-----------------------------------------|
> + *
> + * @retval EFI_SUCCESS      Successfully initialize the reserved memory.
> + * @retval EFI_UNSUPPORTED  This feature is not supported.
> + */
> +EFI_STATUS
> +IoMmuInitReservedSharedMem (
> +  VOID
> +  )
> +{
> +  EFI_STATUS                Status;
> +  UINT32                    Index1, Index2;
> +  UINTN                     TotalPages;
> +  IOMMU_RESERVED_MEM_RANGE  *MemRange;
> +  EFI_PHYSICAL_ADDRESS      PhysicalAddress;
> +
> +  if (!mReservedSharedMemSupported) {
> +    return EFI_UNSUPPORTED;
> +  }
> +
> +  TotalPages = EFI_SIZE_TO_PAGES (CalcuateReservedMemSize ());
> +
> +  PhysicalAddress = (EFI_PHYSICAL_ADDRESS)(UINTN)AllocatePages (TotalPages);
> +  DEBUG ((
> +    DEBUG_VERBOSE,
> +    "%a: ReservedMem (%d pages) address = 0x%llx\n",
> +    __FUNCTION__,
> +    TotalPages,
> +    PhysicalAddress
> +    ));
> +
> +  mReservedMemBitmap        = 0;
> +  mReservedSharedMemAddress = PhysicalAddress;
> +
> +  for (Index1 = 0; Index1 < ARRAY_SIZE (mReservedMemRanges); Index1++) {
> +    MemRange                         = &mReservedMemRanges[Index1];
> +    MemRange->StartAddressOfMemRange = PhysicalAddress;
> +
> +    for (Index2 = 0; Index2 < MemRange->Slots; Index2++) {
> +      Status = MemEncryptTdxSetPageSharedBit (
> +                 0,
> +                 (UINT64)(UINTN)(MemRange->StartAddressOfMemRange + Index2 * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize),
> +                 EFI_SIZE_TO_PAGES (MemRange->DataSize)
> +                 );
> +      ASSERT (!EFI_ERROR (Status));
> +    }
> +
> +    PhysicalAddress += (MemRange->Slots * SIZE_OF_MEM_RANGE (MemRange));
> +  }
> +
> +  return EFI_SUCCESS;
> +}
> +
> +/**
> + * Release the pre-alloc shared memory.
> + *
> + * @retval EFI_SUCCESS  Successfully release the shared memory
> + */
> +EFI_STATUS
> +IoMmuReleaseReservedSharedMem (
> +  BOOLEAN  MemoryMapLocked
> +  )
> +{
> +  EFI_STATUS                Status;
> +  UINT32                    Index1, Index2;
> +  IOMMU_RESERVED_MEM_RANGE  *MemRange;
> +
> +  for (Index1 = 0; Index1 < ARRAY_SIZE (mReservedMemRanges); Index1++) {
> +    MemRange = &mReservedMemRanges[Index1];
> +    for (Index2 = 0; Index2 < MemRange->Slots; Index2++) {
> +      Status = MemEncryptTdxClearPageSharedBit (
> +                 0,
> +                 (UINT64)(UINTN)(MemRange->StartAddressOfMemRange + Index2 * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize),
> +                 EFI_SIZE_TO_PAGES (MemRange->DataSize)
> +                 );
> +      ASSERT (!EFI_ERROR (Status));
> +    }
> +  }
> +
> +  if (!MemoryMapLocked) {
> +    FreePages ((VOID *)(UINTN)mReservedSharedMemAddress, EFI_SIZE_TO_PAGES (CalcuateReservedMemSize ()));
> +    mReservedSharedMemAddress = 0;
> +    mReservedMemBitmap        = 0;
> +  }
> +
> +  return EFI_SUCCESS;
> +}
> +
> +/**
> + * Allocate from the reserved memory pool.
> + * If the reserved shared memory is exausted or there is no suitalbe size, it turns
> + * to the LegacyAllocateBuffer.
> + *
> + * @param Type                Allocate type
> + * @param MemoryType          The memory type to be allocated
> + * @param Pages               Pages to be allocated.
> + * @param ReservedMemBitmap   Bitmap of the allocated memory region
> + * @param PhysicalAddress     Pointer to the data part of allocated memory region
> + *
> + * @retval EFI_SUCCESS        Successfully allocate the buffer
> + * @retval Other              As the error code indicates
> + */
> +STATIC
> +EFI_STATUS
> +InternalAllocateBuffer (
> +  IN  EFI_ALLOCATE_TYPE        Type,
> +  IN  EFI_MEMORY_TYPE          MemoryType,
> +  IN  UINTN                    Pages,
> +  IN OUT UINT32                *ReservedMemBitmap,
> +  IN OUT EFI_PHYSICAL_ADDRESS  *PhysicalAddress
> +  )
> +{
> +  UINT32                    MemBitmap;
> +  UINT8                     Index;
> +  IOMMU_RESERVED_MEM_RANGE  *MemRange;
> +  UINTN                     PagesOfLastMemRange;
> +
> +  *ReservedMemBitmap = 0;
> +
> +  if (Pages == 0) {
> +    ASSERT (FALSE);
> +    return EFI_INVALID_PARAMETER;
> +  }
> +
> +  if (!mReservedSharedMemSupported) {
> +    goto LegacyAllocateBuffer;
> +  }
> +
> +  if (mReservedSharedMemAddress == 0) {
> +    goto LegacyAllocateBuffer;
> +  }
> +
> +  PagesOfLastMemRange = 0;
> +
> +  for (Index = 0; Index < ARRAY_SIZE (mReservedMemRanges); Index++) {
> +    if ((Pages > PagesOfLastMemRange) && (Pages <= EFI_SIZE_TO_PAGES (mReservedMemRanges[Index].DataSize))) {
> +      break;
> +    }
> +
> +    PagesOfLastMemRange = EFI_SIZE_TO_PAGES (mReservedMemRanges[Index].DataSize);
> +  }
> +
> +  if (Index == ARRAY_SIZE (mReservedMemRanges)) {
> +    // There is no suitable size of reserved memory. Turn to legacy allocate.
> +    goto LegacyAllocateBuffer;
> +  }
> +
> +  MemRange = &mReservedMemRanges[Index];
> +
> +  if ((mReservedMemBitmap & MemRange->BitmapMask) == MemRange->BitmapMask) {
> +    // The reserved memory is exausted. Turn to legacy allocate.
> +    goto LegacyAllocateBuffer;
> +  }
> +
> +  MemBitmap = (mReservedMemBitmap & MemRange->BitmapMask) >> MemRange->Shift;
> +
> +  for (Index = 0; Index < MemRange->Slots; Index++) {
> +    if ((MemBitmap & (UINT8)(1<<Index)) == 0) {
> +      break;
> +    }
> +  }
> +
> +  ASSERT (Index != MemRange->Slots);
> +
> +  *PhysicalAddress   = MemRange->StartAddressOfMemRange + Index * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize;
> +  *ReservedMemBitmap = (UINT32)(1 << (Index + MemRange->Shift));
> +
> +  DEBUG ((
> +    DEBUG_VERBOSE,
> +    "%a: range-size: %lx, start-address=0x%llx, pages=0x%llx, bits=0x%lx, bitmap: %lx => %lx\n",
> +    __FUNCTION__,
> +    MemRange->DataSize,
> +    *PhysicalAddress,
> +    Pages,
> +    *ReservedMemBitmap,
> +    mReservedMemBitmap,
> +    mReservedMemBitmap | *ReservedMemBitmap
> +    ));
> +
> +  return EFI_SUCCESS;
> +
> +LegacyAllocateBuffer:
> +
> +  *ReservedMemBitmap = 0;
> +  return gBS->AllocatePages (Type, MemoryType, Pages, PhysicalAddress);
> +}
> +
> +/**
> + * Allocate reserved shared memory for bounce buffer.
> + *
> + * @param Type        Allocate type
> + * @param MemoryType  The memory type to be allocated
> + * @param MapInfo     Pointer to the MAP_INFO
> + *
> + * @retval EFI_SUCCESS        Successfully allocate the bounce buffer
> + * @retval Other              As the error code indicates
> +
> + */
> +EFI_STATUS
> +IoMmuAllocateBounceBuffer (
> +  IN     EFI_ALLOCATE_TYPE  Type,
> +  IN     EFI_MEMORY_TYPE    MemoryType,
> +  IN OUT MAP_INFO           *MapInfo
> +  )
> +{
> +  EFI_STATUS  Status;
> +  UINT32      ReservedMemBitmap;
> +
> +  ReservedMemBitmap = 0;
> +  Status            = InternalAllocateBuffer (
> +                        Type,
> +                        MemoryType,
> +                        MapInfo->NumberOfPages,
> +                        &ReservedMemBitmap,
> +                        &MapInfo->PlainTextAddress
> +                        );
> +  MapInfo->ReservedMemBitmap = ReservedMemBitmap;
> +  mReservedMemBitmap        |= ReservedMemBitmap;
> +
> +  ASSERT (Status == EFI_SUCCESS);
> +
> +  return Status;
> +}
> +
> +/**
> + * Free the bounce buffer allocated in IoMmuAllocateBounceBuffer.
> + *
> + * @param MapInfo       Pointer to the MAP_INFO
> + * @return EFI_SUCCESS  Successfully free the bounce buffer.
> + */
> +EFI_STATUS
> +IoMmuFreeBounceBuffer (
> +  IN OUT     MAP_INFO  *MapInfo
> +  )
> +{
> +  if (MapInfo->ReservedMemBitmap == 0) {
> +    gBS->FreePages (MapInfo->PlainTextAddress, MapInfo->NumberOfPages);
> +  } else {
> +    DEBUG ((
> +      DEBUG_VERBOSE,
> +      "%a: PlainTextAddress=0x%Lx, bits=0x%Lx, bitmap: %Lx => %Lx\n",
> +      __FUNCTION__,
> +      MapInfo->PlainTextAddress,
> +      MapInfo->ReservedMemBitmap,
> +      mReservedMemBitmap,
> +      mReservedMemBitmap & ((UINT32)(~MapInfo->ReservedMemBitmap))
> +      ));
> +    MapInfo->PlainTextAddress  = 0;
> +    mReservedMemBitmap        &= (UINT32)(~MapInfo->ReservedMemBitmap);
> +    MapInfo->ReservedMemBitmap = 0;
> +  }
> +
> +  return EFI_SUCCESS;
> +}
> +
> +/**
> + * Allocate CommonBuffer from pre-allocated shared memory.
> + *
> + * @param MemoryType          Memory type
> + * @param CommonBufferPages   Pages of CommonBuffer
> + * @param PhysicalAddress     Allocated physical address
> + * @param ReservedMemBitmap   Bitmap which indicates the allocation of reserved memory
> + *
> + * @retval EFI_SUCCESS        Successfully allocate the common buffer
> + * @retval Other              As the error code indicates
> + */
> +EFI_STATUS
> +IoMmuAllocateCommonBuffer (
> +  IN EFI_MEMORY_TYPE        MemoryType,
> +  IN UINTN                  CommonBufferPages,
> +  OUT EFI_PHYSICAL_ADDRESS  *PhysicalAddress,
> +  OUT UINT32                *ReservedMemBitmap
> +  )
> +{
> +  EFI_STATUS  Status;
> +
> +  Status = InternalAllocateBuffer (
> +             AllocateMaxAddress,
> +             MemoryType,
> +             CommonBufferPages,
> +             ReservedMemBitmap,
> +             PhysicalAddress
> +             );
> +  ASSERT (Status == EFI_SUCCESS);
> +
> +  mReservedMemBitmap |= *ReservedMemBitmap;
> +
> +  if (*ReservedMemBitmap != 0) {
> +    *PhysicalAddress -= SIZE_4KB;
> +  }
> +
> +  return Status;
> +}
> +
> +/**
> + * Free CommonBuffer which is allocated by IoMmuAllocateCommonBuffer().
> + *
> + * @param CommonBufferHeader  Pointer to the CommonBufferHeader
> + * @param CommonBufferPages   Pages of CommonBuffer
> + *
> + * @retval EFI_SUCCESS        Successfully free the common buffer
> + * @retval Other              As the error code indicates
> + */
> +EFI_STATUS
> +IoMmuFreeCommonBuffer (
> +  IN COMMON_BUFFER_HEADER  *CommonBufferHeader,
> +  IN UINTN                 CommonBufferPages
> +  )
> +{
> +  if (!mReservedSharedMemSupported) {
> +    goto LegacyFreeCommonBuffer;
> +  }
> +
> +  if (CommonBufferHeader->ReservedMemBitmap == 0) {
> +    goto LegacyFreeCommonBuffer;
> +  }
> +
> +  DEBUG ((
> +    DEBUG_VERBOSE,
> +    "%a: CommonBuffer=0x%Lx, bits=0x%Lx, bitmap: %Lx => %Lx\n",
> +    __FUNCTION__,
> +    (UINT64)(UINTN)CommonBufferHeader + SIZE_4KB,
> +    CommonBufferHeader->ReservedMemBitmap,
> +    mReservedMemBitmap,
> +    mReservedMemBitmap & ((UINT32)(~CommonBufferHeader->ReservedMemBitmap))
> +    ));
> +
> +  mReservedMemBitmap &= (UINT32)(~CommonBufferHeader->ReservedMemBitmap);
> +  return EFI_SUCCESS;
> +
> +LegacyFreeCommonBuffer:
> +  return gBS->FreePages ((UINTN)CommonBufferHeader, CommonBufferPages);
> +}
> diff --git a/OvmfPkg/IoMmuDxe/IoMmuDxe.inf b/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
> index e10be1dcff49..2192145ea661 100644
> --- a/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
> +++ b/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
> @@ -21,6 +21,7 @@
>     AmdSevIoMmu.c
>     AmdSevIoMmu.h
>     IoMmuDxe.c
> +  IoMmuBuffer.c
>   
>   [Packages]
>     MdePkg/MdePkg.dec
> diff --git a/OvmfPkg/IoMmuDxe/IoMmuInternal.h b/OvmfPkg/IoMmuDxe/IoMmuInternal.h
> new file mode 100644
> index 000000000000..936c35aa536c
> --- /dev/null
> +++ b/OvmfPkg/IoMmuDxe/IoMmuInternal.h
> @@ -0,0 +1,179 @@
> +/** @file
> +
> +  Copyright (c) 2022, Intel Corporation. All rights reserved.<BR>
> +
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#ifndef IOMMU_INTERNAL_H_
> +#define IOMMU_INTERNAL_H_
> +
> +#include <Base.h>
> +#include <Protocol/IoMmu.h>
> +#include <Uefi/UefiBaseType.h>
> +#include <Uefi/UefiSpec.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;
> +  UINT32                   ReservedMemBitmap;
> +} MAP_INFO;
> +
> +#define COMMON_BUFFER_SIG  SIGNATURE_64 ('C', 'M', 'N', 'B', 'U', 'F', 'F', 'R')
> +
> +#pragma pack (1)
> +//
> +// 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().
> +//
> +typedef struct {
> +  UINT64    Signature;
> +
> +  //
> +  // Always allocated from EfiBootServicesData type memory, and always
> +  // encrypted.
> +  //
> +  VOID      *StashBuffer;
> +
> +  //
> +  // Bitmap of reserved memory
> +  //
> +  UINT32    ReservedMemBitmap;
> +
> +  //
> +  // Followed by the actual common buffer, starting at the next page.
> +  //
> +} COMMON_BUFFER_HEADER;
> +
> +//
> +// This data structure defines a memory range in the reserved memory region.
> +// Please refer to IoMmuInitReservedSharedMem() for detailed information.
> +//
> +// The memory region looks like:
> +//     |------------|----------------------------|
> +//     | Header     |    Data                    |
> +//     | 4k, private| 4k/32k/128k/etc, shared    |
> +//     |-----------------------------------------|
> +//
> +typedef struct {
> +  UINT32                  BitmapMask;
> +  UINT32                  Shift;
> +  UINT32                  Slots;
> +  UINT32                  DataSize;
> +  UINT32                  HeaderSize;
> +  EFI_PHYSICAL_ADDRESS    StartAddressOfMemRange;
> +} IOMMU_RESERVED_MEM_RANGE;
> +#pragma pack()
> +
> +/**
> + * Allocate a memory region and convert it to be shared. This memory region will be
> + * used in the DMA operation.
> + *
> + * The pre-alloc memory contains pieces of memory regions with different size. The
> + * allocation of the shared memory regions are indicated by a 32-bit bitmap (mReservedMemBitmap).
> + *
> + * The memory regions are consumed by IoMmuAllocateBuffer (in which CommonBuffer is allocated) and
> + * IoMmuMap (in which bounce buffer is allocated).
> + *
> + * The CommonBuffer contains 2 parts, one page for CommonBufferHeader which is private memory,
> + * the other part is shared memory. So the layout of a piece of memory region after initialization
> + * looks like:
> + *
> + *     |------------|----------------------------|
> + *     | Header     |    Data                    |  <-- a piece of pre-alloc memory region
> + *     | 4k, private| 4k/32k/128k/etc, shared    |
> + *     |-----------------------------------------|
> + *
> + * @retval EFI_SUCCESS      Successfully initialize the reserved memory.
> + * @retval EFI_UNSUPPORTED  This feature is not supported.
> + */
> +EFI_STATUS
> +IoMmuInitReservedSharedMem (
> +  VOID
> +  );
> +
> +/**
> + * Release the pre-alloc shared memory.
> + *
> + * @retval EFI_SUCCESS  Successfully release the shared memory
> + */
> +EFI_STATUS
> +IoMmuReleaseReservedSharedMem (
> +  BOOLEAN  MemoryMapLocked
> +  );
> +
> +/**
> + * Allocate reserved shared memory for bounce buffer.
> + *
> + * @param Type        Allocate type
> + * @param MemoryType  The memory type to be allocated
> + * @param MapInfo     Pointer to the MAP_INFO
> + *
> + * @retval EFI_SUCCESS        Successfully allocate the bounce buffer
> + * @retval Other              As the error code indicates
> + */
> +EFI_STATUS
> +IoMmuAllocateBounceBuffer (
> +  IN     EFI_ALLOCATE_TYPE  Type,
> +  IN     EFI_MEMORY_TYPE    MemoryType,
> +  IN OUT MAP_INFO           *MapInfo
> +  );
> +
> +/**
> + * Free the bounce buffer allocated in IoMmuAllocateBounceBuffer.
> + *
> + * @param MapInfo       Pointer to the MAP_INFO
> + * @return EFI_SUCCESS  Successfully free the bounce buffer.
> + */
> +EFI_STATUS
> +IoMmuFreeBounceBuffer (
> +  IN OUT     MAP_INFO  *MapInfo
> +  );
> +
> +/**
> + * Allocate CommonBuffer from pre-allocated shared memory.
> + *
> + * @param MemoryType          Memory type
> + * @param CommonBufferPages   Pages of CommonBuffer
> + * @param PhysicalAddress     Allocated physical address
> + * @param ReservedMemBitmap   Bitmap which indicates the allocation of reserved memory
> + *
> + * @retval EFI_SUCCESS        Successfully allocate the common buffer
> + * @retval Other              As the error code indicates
> + */
> +EFI_STATUS
> +IoMmuAllocateCommonBuffer (
> +  IN EFI_MEMORY_TYPE        MemoryType,
> +  IN UINTN                  CommonBufferPages,
> +  OUT EFI_PHYSICAL_ADDRESS  *PhysicalAddress,
> +  OUT UINT32                *ReservedMemBitmap
> +  );
> +
> +/**
> + * Free CommonBuffer which is allocated by IoMmuAllocateCommonBuffer().
> + *
> + * @param CommonBufferHeader  Pointer to the CommonBufferHeader
> + * @param CommonBufferPages   Pages of CommonBuffer
> + *
> + * @retval EFI_SUCCESS        Successfully free the common buffer
> + * @retval Other              As the error code indicates
> + */
> +EFI_STATUS
> +IoMmuFreeCommonBuffer (
> +  IN COMMON_BUFFER_HEADER  *CommonBufferHeader,
> +  IN UINTN                 CommonBufferPages
> +  );
> +
> +#endif