SecVmgExitVcHandler.c

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#include <Base.h>
#include <Uefi.h>
#include <Library/BaseMemoryLib.h>
#include <Library/MemEncryptSevLib.h>
#include <Library/VmgExitLib.h>
#include <Register/Amd/Msr.h>
 
#include "VmgExitVcHandler.h"
 
EFI_STATUS
EFIAPI
VmgExitHandleVc (
  IN OUT EFI_EXCEPTION_TYPE  *ExceptionType,
  IN OUT EFI_SYSTEM_CONTEXT  SystemContext
  )
{
  MSR_SEV_ES_GHCB_REGISTER  Msr;
  GHCB                      *Ghcb;
  GHCB                      *GhcbBackup;
  EFI_STATUS                VcRet;
  BOOLEAN                   InterruptState;
  SEV_ES_PER_CPU_DATA       *SevEsData;
 
  InterruptState = GetInterruptState ();
  if (InterruptState) {
    DisableInterrupts ();
  }
 
  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
  ASSERT (Msr.GhcbInfo.Function == 0);
  ASSERT (Msr.Ghcb != 0);
 
  Ghcb       = Msr.Ghcb;
  GhcbBackup = NULL;
 
  SevEsData = (SEV_ES_PER_CPU_DATA *)(Ghcb + 1);
  SevEsData->VcCount++;
 
  //
  // Check for maximum SEC #VC nesting.
  //
  if (SevEsData->VcCount > VMGEXIT_MAXIMUM_VC_COUNT) {
    VmgExitIssueAssert (SevEsData);
  } else if (SevEsData->VcCount > 1) {
    UINTN  GhcbBackupSize;
 
    //
    // Be sure that the proper amount of pages are allocated
    //
    GhcbBackupSize = (VMGEXIT_MAXIMUM_VC_COUNT - 1) * sizeof (*Ghcb);
    if (GhcbBackupSize > FixedPcdGet32 (PcdOvmfSecGhcbBackupSize)) {
      //
      // Not enough SEC backup pages allocated.
      //
      VmgExitIssueAssert (SevEsData);
    }
 
    //
    // Save the active GHCB to a backup page.
    //   To access the correct backup page, increment the backup page pointer
    //   based on the current VcCount.
    //
    GhcbBackup  = (GHCB *)FixedPcdGet32 (PcdOvmfSecGhcbBackupBase);
    GhcbBackup += (SevEsData->VcCount - 2);
 
    CopyMem (GhcbBackup, Ghcb, sizeof (*Ghcb));
  }
 
  VcRet = InternalVmgExitHandleVc (Ghcb, ExceptionType, SystemContext);
 
  if (GhcbBackup != NULL) {
    //
    // Restore the active GHCB from the backup page.
    //
    CopyMem (Ghcb, GhcbBackup, sizeof (*Ghcb));
  }
 
  SevEsData->VcCount--;
 
  if (InterruptState) {
    EnableInterrupts ();
  }
 
  return VcRet;
}