OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlashDxe.c

   1 /** @file
   2   OVMF support for QEMU system firmware flash device: functions specific to the
   3   runtime DXE driver build.
   4
   5   Copyright (C) 2015, Red Hat, Inc.
   6   Copyright (c) 2009 - 2013, Intel Corporation. All rights reserved.<BR>
   7
   8   SPDX-License-Identifier: BSD-2-Clause-Patent
   9
  10 **/
  11
  12 #include <Library/UefiRuntimeLib.h>
  13 #include <Library/MemEncryptSevLib.h>
  14 #include <Library/VmgExitLib.h>
  15 #include <Register/Amd/Msr.h>
  16
  17 #include "QemuFlash.h"
  18
  19 VOID
  20 QemuFlashConvertPointers (
  21   VOID
  22   )
  23 {
  24   EfiConvertPointer (0x0, (VOID **) &mFlashBase);
  25 }
  26
  27 VOID
  28 QemuFlashBeforeProbe (
  29   IN  EFI_PHYSICAL_ADDRESS    BaseAddress,
  30   IN  UINTN                   FdBlockSize,
  31   IN  UINTN                   FdBlockCount
  32   )
  33 {
  34   //
  35   // Do nothing
  36   //
  37 }
  38
  39 /**
  40   Write to QEMU Flash
  41
  42   @param[in] Ptr    Pointer to the location to write.
  43   @param[in] Value  The value to write.
  44
  45 **/
  46 VOID
  47 QemuFlashPtrWrite (
  48   IN        volatile UINT8    *Ptr,
  49   IN        UINT8             Value
  50   )
  51 {
  52   if (MemEncryptSevEsIsEnabled ()) {
  53     MSR_SEV_ES_GHCB_REGISTER  Msr;
  54     GHCB                      *Ghcb;
  55
  56     Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
  57     Ghcb = Msr.Ghcb;
  58
  59     //
  60     // Writing to flash is emulated by the hypervisor through the use of write
  61     // protection. This won't work for an SEV-ES guest because the write won't
  62     // be recognized as a true MMIO write, which would result in the required
  63     // #VC exception. Instead, use the the VMGEXIT MMIO write support directly
  64     // to perform the update.
  65     //
  66     VmgInit (Ghcb);
  67     Ghcb->SharedBuffer[0] = Value;
  68     Ghcb->SaveArea.SwScratch = (UINT64) (UINTN) Ghcb->SharedBuffer;
  69     VmgExit (Ghcb, SVM_EXIT_MMIO_WRITE, (UINT64) (UINTN) Ptr, 1);
  70     VmgDone (Ghcb);
  71   } else {
  72     *Ptr = Value;
  73   }
  74 }