[PATCH 2/2] OvmfPkg/QemuFlashFvbServicesRuntimeDxe: Clear C-bit when SEV is active

[Brijesh Singh <brijesh.singh@amd.com>]

Commit:24e4ad7 (OvmfPkg: Add AmdSevDxe driver) added a driver which runs
early in PEI phase and clears the C-bit from all MMIO regions (including
Qemu Flash). When SMM is enabled, we build two sets of page tables; first
page table is used when executing code in non SMM mode (SMM-less-pgtable)
and second page table is used when we are executing code in SMM mode
(SMM-pgtable).

During boot time, AmdSevDxe driver clears the C-bit from the
SMM-less-pgtable. But when SMM is enabled, Qemu Flash services are used
from SMM mode.

In this patch we explicitly clear the C-bit from Qemu flash MMIO range
before we probe the flash. When OVMF is built with SMM_REQUIRE then
call to initialize the flash services happen after the SMM-pgtable is
created and processor is serving the first SMI. At this time we will
have access to the SMM-pgtable.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesSmm.inf  |  1 +
 OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.h    |  5 +++
 OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c    |  5 +++
 OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c | 10 ++++++
 OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceSmm.c | 35 ++++++++++++++++++++
 5 files changed, 56 insertions(+)

diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesSmm.inf b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesSmm.inf
index ba2d3679a46d..d365e27cbe59 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesSmm.inf
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesSmm.inf
@@ -53,6 +53,7 @@ [LibraryClasses]
   DevicePathLib
   DxeServicesTableLib
   MemoryAllocationLib
+  MemEncryptSevLib
   PcdLib
   SmmServicesTableLib
   UefiBootServicesTableLib
diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.h b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.h
index 1f9287b08769..704ed477ba14 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.h
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.h
@@ -189,4 +189,9 @@ VOID
 InstallVirtualAddressChangeHandler (
   VOID
   );
+
+VOID
+FvbBeforeFlashProbe (
+  VOID
+  );
 #endif
diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c
index 558b395dff4a..b7b9bf1fb8d9 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c
@@ -967,6 +967,11 @@ FvbInitialize (
   UINTN                               NumOfBlocks;
   RETURN_STATUS                       PcdStatus;
 
+  //
+  // execute platform specific hooks before probing the flash
+  //
+  FvbBeforeFlashProbe ();
+
   if (EFI_ERROR (QemuFlashInitialize ())) {
     //
     // Return an error so image will be unloaded
diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
index 63b308658e36..7d274c08ad12 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
@@ -155,3 +155,13 @@ InstallVirtualAddressChangeHandler (
                   );
   ASSERT_EFI_ERROR (Status);
 }
+
+VOID
+FvbBeforeFlashProbe (
+  VOID
+  )
+{
+  //
+  // Do nothing
+  //
+}
diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceSmm.c b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceSmm.c
index e0617f2503a2..d97b13f47bf7 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceSmm.c
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceSmm.c
@@ -17,6 +17,7 @@
 #include <Library/DebugLib.h>
 #include <Library/PcdLib.h>
 #include <Library/SmmServicesTableLib.h>
+#include <Library/MemEncryptSevLib.h>
 #include <Protocol/DevicePath.h>
 #include <Protocol/SmmFirmwareVolumeBlock.h>
 
@@ -67,3 +68,37 @@ InstallVirtualAddressChangeHandler (
   // Nothing.
   //
 }
+
+VOID
+FvbBeforeFlashProbe (
+  VOID
+  )
+{
+
+  ASSERT (FeaturePcdGet (PcdSmmSmramRequire));
+
+  //
+  // When SEV is enabled, AmdSevDxe runs early in PEI phase and clears the C-bit
+  // from the MMIO space (including flash ranges) but the driver runs in non SMM
+  // context hence it cleared the flash ranges from non SMM page table.
+  // When SMM is enabled, the flash services are accessed from the SMM mode
+  // hence we explicitly clear the C-bit on flash ranges from SMM page table.
+  //
+  if (MemEncryptSevIsEnabled ()) {
+    EFI_STATUS              Status;
+    EFI_PHYSICAL_ADDRESS    BaseAddress;
+    UINTN                   FdBlockSize, FdBlockCount;
+
+    BaseAddress = (EFI_PHYSICAL_ADDRESS) PcdGet32 (PcdOvmfFdBaseAddress);
+    FdBlockSize = PcdGet32 (PcdOvmfFirmwareBlockSize);
+    FdBlockCount = PcdGet32 (PcdOvmfFirmwareFdSize) / FdBlockSize;
+
+    Status = MemEncryptSevClearPageEncMask (
+               0,
+               BaseAddress,
+               EFI_SIZE_TO_PAGES (FdBlockSize * FdBlockCount),
+               FALSE
+              );
+    ASSERT_EFI_ERROR (Status);
+  }
+}
-- 
2.14.3