QemuFlashDxe.c

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#include <Library/UefiRuntimeLib.h>
#include <Library/MemEncryptSevLib.h>
#include <Library/CcExitLib.h>
#include <Register/Amd/Msr.h>
 
#include "QemuFlash.h"
 
STATIC EFI_PHYSICAL_ADDRESS  mSevEsFlashPhysBase;
 
VOID
QemuFlashConvertPointers (
  VOID
  )
{
  if (MemEncryptSevEsIsEnabled ()) {
    mSevEsFlashPhysBase = (UINTN)mFlashBase;
  }
 
  EfiConvertPointer (0x0, (VOID **)&mFlashBase);
}
 
VOID
QemuFlashBeforeProbe (
  IN  EFI_PHYSICAL_ADDRESS  BaseAddress,
  IN  UINTN                 FdBlockSize,
  IN  UINTN                 FdBlockCount
  )
{
  //
  // Do nothing
  //
}
 
VOID
QemuFlashPtrWrite (
  IN        volatile UINT8  *Ptr,
  IN        UINT8           Value
  )
{
  if (MemEncryptSevEsIsEnabled ()) {
    MSR_SEV_ES_GHCB_REGISTER  Msr;
    GHCB                      *Ghcb;
    EFI_PHYSICAL_ADDRESS      PhysAddr;
    BOOLEAN                   InterruptState;
 
    Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
    Ghcb                    = Msr.Ghcb;
 
    //
    // The MMIO write needs to be to the physical address of the flash pointer.
    // Since this service is available as part of the EFI runtime services,
    // account for a non-identity mapped VA after SetVirtualAddressMap().
    //
    if (mSevEsFlashPhysBase == 0) {
      PhysAddr = (UINTN)Ptr;
    } else {
      PhysAddr = mSevEsFlashPhysBase + (Ptr - mFlashBase);
    }
 
    //
    // Writing to flash is emulated by the hypervisor through the use of write
    // protection. This won't work for an SEV-ES guest because the write won't
    // be recognized as a true MMIO write, which would result in the required
    // #VC exception. Instead, use the VMGEXIT MMIO write support directly
    // to perform the update.
    //
    CcExitVmgInit (Ghcb, &InterruptState);
    Ghcb->SharedBuffer[0]    = Value;
    Ghcb->SaveArea.SwScratch = (UINT64)(UINTN)Ghcb->SharedBuffer;
    CcExitVmgSetOffsetValid (Ghcb, GhcbSwScratch);
    CcExitVmgExit (Ghcb, SVM_EXIT_MMIO_WRITE, PhysAddr, 1);
    CcExitVmgDone (Ghcb, InterruptState);
  } else {
    *Ptr = Value;
  }
}