OvmfPkg/QemuFwCfgLib: Implement SEV internal function for Dxe phase

When SEV is enabled, the DMA must be performed on unencrypted pages.
So when get asked to perfom FWCFG DMA read or write, we allocate a
intermediate (bounce buffer) unencrypted buffer and use this buffer
for DMA read or write.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxe.c

@@ -4,6 +4,7 @@
 
   Copyright (C) 2013, Red Hat, Inc.
   Copyright (c) 2011 - 2013, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2017, Advanced Micro Devices. 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
@@ -14,14 +15,36 @@
   WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 **/
 
+#include <Uefi.h>
+
+#include <Protocol/IoMmu.h>
+
+#include <Library/BaseLib.h>
 #include <Library/DebugLib.h>
 #include <Library/QemuFwCfgLib.h>
+#include <Library/UefiBootServicesTableLib.h>
+#include <Library/MemEncryptSevLib.h>
 
 #include "QemuFwCfgLibInternal.h"
 
 STATIC BOOLEAN mQemuFwCfgSupported = FALSE;
 STATIC BOOLEAN mQemuFwCfgDmaSupported;
 
+STATIC EDKII_IOMMU_PROTOCOL        *mIoMmuProtocol;
+/**
+
+ Returns a boolean indicating whether SEV is enabled
+
+ @retval    TRUE    SEV is enabled
+ @retval    FALSE   SEV is disabled
+**/
+BOOLEAN
+InternalQemuFwCfgSevIsEnabled (
+  VOID
+  )
+{
+  return MemEncryptSevIsEnabled ();
+}
 
 /**
   Returns a boolean indicating if the firmware configuration interface
@@ -79,6 +102,24 @@ QemuFwCfgInitialize (
     mQemuFwCfgDmaSupported = TRUE;
     DEBUG ((DEBUG_INFO, "QemuFwCfg interface (DMA) is supported.\n"));
   }
+
+  if (mQemuFwCfgDmaSupported && MemEncryptSevIsEnabled ()) {
+    EFI_STATUS   Status;
+
+    //
+    // IoMmuDxe driver must have installed the IOMMU protocol. If we are not
+    // able to locate the protocol then something must have gone wrong.
+    //
+    Status = gBS->LocateProtocol (&gEdkiiIoMmuProtocolGuid, NULL, (VOID **)&mIoMmuProtocol);
+    if (EFI_ERROR (Status)) {
+      DEBUG ((DEBUG_ERROR,
+        "QemuFwCfgSevDma %a:%a Failed to locate IOMMU protocol.\n",
+        gEfiCallerBaseName, __FUNCTION__));
+      ASSERT (FALSE);
+      CpuDeadLoop ();
+    }
+  }
+
   return RETURN_SUCCESS;
 }
 
@@ -114,3 +155,76 @@ InternalQemuFwCfgDmaIsAvailable (
 {
   return mQemuFwCfgDmaSupported;
 }
+
+/**
+ Allocate a bounce buffer for SEV DMA.
+
+  @param[in]     NumPage  Number of pages.
+  @param[out]    Buffer   Allocated DMA Buffer pointer
+
+**/
+VOID
+InternalQemuFwCfgSevDmaAllocateBuffer (
+  OUT    VOID     **Buffer,
+  IN     UINT32   NumPages
+  )
+{
+  EFI_STATUS    Status;
+
+  ASSERT (mIoMmuProtocol != NULL);
+
+  Status = mIoMmuProtocol->AllocateBuffer (
+                            mIoMmuProtocol,
+                            0,
+                            EfiBootServicesData,
+                            NumPages,
+                            Buffer,
+                            EDKII_IOMMU_ATTRIBUTE_MEMORY_CACHED
+                          );
+  if (EFI_ERROR (Status)) {
+    DEBUG ((DEBUG_ERROR,
+      "%a:%a failed to allocate %u pages\n", gEfiCallerBaseName, __FUNCTION__,
+      NumPages));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+  }
+
+  DEBUG ((DEBUG_VERBOSE,
+    "%a:%a buffer 0x%Lx Pages %u\n", gEfiCallerBaseName, __FUNCTION__,
+    (UINT64)(UINTN)Buffer, NumPages));
+}
+
+/**
+ Free the DMA buffer allocated using InternalQemuFwCfgSevDmaAllocateBuffer
+
+  @param[in]     NumPage  Number of pages.
+  @param[in]     Buffer   DMA Buffer pointer
+
+**/
+VOID
+InternalQemuFwCfgSevDmaFreeBuffer (
+  IN     VOID     *Buffer,
+  IN     UINT32   NumPages
+  )
+{
+  EFI_STATUS    Status;
+
+  ASSERT (mIoMmuProtocol != NULL);
+
+  Status = mIoMmuProtocol->FreeBuffer (
+                            mIoMmuProtocol,
+                            NumPages,
+                            Buffer
+                          );
+  if (EFI_ERROR (Status)) {
+    DEBUG ((DEBUG_ERROR,
+      "%a:%a failed to free buffer 0x%Lx pages %u\n", gEfiCallerBaseName,
+      __FUNCTION__, (UINT64)(UINTN)Buffer, NumPages));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+  }
+
+  DEBUG ((DEBUG_VERBOSE,
+    "%a:%a buffer 0x%Lx Pages %u\n", gEfiCallerBaseName,__FUNCTION__,
+    (UINT64)(UINTN)Buffer, NumPages));
+}

OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxeLib.inf

@@ -39,6 +39,7 @@
 
 [Packages]
   MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
   OvmfPkg/OvmfPkg.dec
 
 [LibraryClasses]
@@ -47,4 +48,10 @@
   DebugLib
   IoLib
   MemoryAllocationLib
+  MemEncryptSevLib
 
+[Protocols]
+  gEdkiiIoMmuProtocolGuid                         ## SOMETIMES_CONSUMES
+
+[Depex]
+  gEdkiiIoMmuProtocolGuid OR gIoMmuAbsentProtocolGuid