When SEV is enabled, the DMA operations must be performed on a shared
(i.e unencrypted) pages. The patch adds SEV specific hooks to use the
bounce buffer when caller map/unmap host address to a DMA address and
similarly clears/set memory encryption attribute when caller allocates or
free the DMA pages.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.c   |   60 +++++++++++++++++++++++++++
 OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.inf |    3 +
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.c b/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.c
index 0d960a8..39814cc 100644
--- a/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.c
+++ b/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.c
@@ -25,6 +25,7 @@
 #include <Library/MemoryAllocationLib.h>
 #include <Library/UefiBootServicesTableLib.h>
 #include <Library/BmDmaLib.h>
+#include <Library/MemEncryptSevLib.h>
 
 
 #define FORCE_BELOW_4GB_TRUE   TRUE
@@ -100,6 +101,15 @@ AllocateBounceBuffer (
   }
 
   //
+  // Clear C-bit on DMA pages
+  //
+  if (MemEncryptSevIsEnabled ()) {
+    Status = MemEncryptSevClearPageEncMask (MapInfo->MappedHostAddress, MapInfo->NumberOfPages);
+    if (Status != EFI_SUCCESS) {
+      return Status;
+    }
+  }
+  //
   // 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.
@@ -170,6 +180,23 @@ BmDmaMap (
 
   PhysicalAddress = (EFI_PHYSICAL_ADDRESS) (UINTN) HostAddress;
   if (DmaAbove4GB || (PhysicalAddress + *NumberOfBytes) <= SIZE_4GB) {
+
+    //
+    // When SEV is enabled the DMA operation must be performed on shared pages. We force to use the
+    // bounce buffer path which will take care of allocating shared Dma buffers mapping
+    //
+    if (MemEncryptSevIsEnabled () &&
+        (Operation == DmaOperationBusMasterRead || Operation == DmaOperationBusMasterWrite)) {
+      return AllocateBounceBuffer (
+                                   FORCE_BELOW_4GB_FALSE,
+                                   Operation,
+                                   PhysicalAddress,
+                                   NumberOfBytes,
+                                   DeviceAddress,
+                                   Mapping
+                                   );
+    }
+
     //
     // If we CAN handle DMA above 4GB or the transfer is below 4GB,
     // the DeviceAddress is simply the HostAddress
@@ -218,7 +245,8 @@ BmDmaUnmap (
   IN  VOID                 *Mapping
   )
 {
-  MAP_INFO  *MapInfo;
+  MAP_INFO           *MapInfo;
+  EFI_STATUS         Status;
 
   //
   // Check for invalid inputs
@@ -251,6 +279,17 @@ BmDmaUnmap (
   }
 
   //
+  // When SEV is enabled then Dma buffer allocate by bounce buffer have C-bit cleared,
+  // restore the C-bit before we release the resources
+  //
+  if (MemEncryptSevIsEnabled ()) {
+    Status = MemEncryptSevSetPageEncMask (MapInfo->MappedHostAddress, MapInfo->NumberOfPages);
+    if (Status != EFI_SUCCESS) {
+      return Status;
+    }
+  }
+
+  //
   // Free the mapped buffer and the MAP_INFO structure.
   //
   gBS->FreePages (MapInfo->MappedHostAddress, MapInfo->NumberOfPages);
@@ -322,8 +361,15 @@ BmDmaAllocateBuffer (
                   );
   if (!EFI_ERROR (Status)) {
     *HostAddress = (VOID *) (UINTN) PhysicalAddress;
+    //
+    // Clear C-bit on Dma pages
+    //
+    if (MemEncryptSevIsEnabled ()) {
+      Status = MemEncryptSevClearPageEncMask (PhysicalAddress, Pages);
+    }
   }
 
+
   return Status;
 }
 
@@ -346,6 +392,18 @@ BmDmaFreeBuffer (
   IN  UINTN                Pages
   )
 {
+  EFI_STATUS           Status;
+
+  //
+  // Restore the C-bit on DMA pages
+  //
+  if (MemEncryptSevIsEnabled ()) {
+    Status = MemEncryptSevSetPageEncMask ((UINTN) HostAddress, Pages);
+    if (Status != EFI_SUCCESS) {
+      return Status;
+    }
+  }
+
   return gBS->FreePages ((EFI_PHYSICAL_ADDRESS) (UINTN) HostAddress, Pages);
 }
 
diff --git a/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.inf b/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.inf
index 4ddb27d..fb97caa 100644
--- a/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.inf
+++ b/OvmfPkg/Library/DxeBmDmaLib/DxeBmDmaLib.inf
@@ -29,6 +29,7 @@
 [Packages]
   MdePkg/MdePkg.dec
   MdeModulePkg/MdeModulePkg.dec
+  OvmfPkg/OvmfPkg.dec
 
 [LibraryClasses]
   BaseLib
@@ -37,5 +38,5 @@
   DxeServicesTableLib
   MemoryAllocationLib
   UefiBootServicesTableLib
-
+  MemEncryptSevLib
 

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