OvmfPkg/QemuFlashFvbServicesRuntimeDxe: Restore C-bit when SEV is active

AmdSevDxe maps the flash memory range with C=0, but
SetMemorySpaceAttributes() unconditionally resets the C-bit to '1'. Lets
restore the mapping back to C=0.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Julien Grall <julien.grall@linaro.org>
Cc: Justen Jordan L <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>

2 files changed, 18 insertions, 0 deletions

diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
index d7b4ec06c4..86b244a009 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
@@ -53,6 +53,7 @@
   DebugLib

   DevicePathLib

   DxeServicesTableLib

+  MemEncryptSevLib

   MemoryAllocationLib

   PcdLib

   UefiBootServicesTableLib

diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
index 37deece363..1fbe1342a5 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
@@ -18,6 +18,7 @@
 #include <Library/DebugLib.h>

 #include <Library/DevicePathLib.h>

 #include <Library/DxeServicesTableLib.h>

+#include <Library/MemEncryptSevLib.h>

 #include <Library/PcdLib.h>

 #include <Library/UefiBootServicesTableLib.h>

 #include <Library/UefiRuntimeLib.h>

@@ -203,5 +204,21 @@ MarkIoMemoryRangeForRuntimeAccess (
                   );

   ASSERT_EFI_ERROR (Status);

 

+  //

+  // When SEV is active, AmdSevDxe mapped the BaseAddress with C=0 but

+  // SetMemorySpaceAttributes() remaps the range with C=1. Let's restore

+  // the mapping so that both guest and hyervisor can access the flash

+  // memory range.

+  //

+  if (MemEncryptSevIsEnabled ()) {

+    Status = MemEncryptSevClearPageEncMask (

+               0,

+               BaseAddress,

+               EFI_SIZE_TO_PAGES (Length),

+               FALSE

+               );

+    ASSERT_EFI_ERROR (Status);

+  }

+

   return Status;

 }