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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>
Brijesh Singh %!s(int64=6) %!d(string=hai) anos
pai
achega
75b7aa9528

+ 1 - 0
OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf

@@ -53,6 +53,7 @@
   DebugLib
   DevicePathLib
   DxeServicesTableLib
+  MemEncryptSevLib
   MemoryAllocationLib
   PcdLib
   UefiBootServicesTableLib

+ 17 - 0
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;
 }