OvmfPkg/Library/VmgExitLib/PeiDxeVmgExitVcHandler.c

   1 /** @file
   2   X64 #VC Exception Handler functon.
   3
   4   Copyright (C) 2020, Advanced Micro Devices, Inc. All rights reserved.<BR>
   5   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9 #include <Base.h>
  10 #include <Uefi.h>
  11 #include <Library/BaseMemoryLib.h>
  12 #include <Library/MemEncryptSevLib.h>
  13 #include <Library/VmgExitLib.h>
  14 #include <Register/Amd/Msr.h>
  15
  16 #include "VmgExitVcHandler.h"
  17
  18 /**
  19   Handle a #VC exception.
  20
  21   Performs the necessary processing to handle a #VC exception.
  22
  23   @param[in, out]  ExceptionType  Pointer to an EFI_EXCEPTION_TYPE to be set
  24                                   as value to use on error.
  25   @param[in, out]  SystemContext  Pointer to EFI_SYSTEM_CONTEXT
  26
  27   @retval  EFI_SUCCESS            Exception handled
  28   @retval  EFI_UNSUPPORTED        #VC not supported, (new) exception value to
  29                                   propagate provided
  30   @retval  EFI_PROTOCOL_ERROR     #VC handling failed, (new) exception value to
  31                                   propagate provided
  32
  33 **/
  34 EFI_STATUS
  35 EFIAPI
  36 VmgExitHandleVc (
  37   IN OUT EFI_EXCEPTION_TYPE  *ExceptionType,
  38   IN OUT EFI_SYSTEM_CONTEXT  SystemContext
  39   )
  40 {
  41   MSR_SEV_ES_GHCB_REGISTER  Msr;
  42   GHCB                      *Ghcb;
  43   GHCB                      *GhcbBackup;
  44   EFI_STATUS                VcRet;
  45   BOOLEAN                   InterruptState;
  46   SEV_ES_PER_CPU_DATA       *SevEsData;
  47
  48   InterruptState = GetInterruptState ();
  49   if (InterruptState) {
  50     DisableInterrupts ();
  51   }
  52
  53   Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
  54   ASSERT (Msr.GhcbInfo.Function == 0);
  55   ASSERT (Msr.Ghcb != 0);
  56
  57   Ghcb       = Msr.Ghcb;
  58   GhcbBackup = NULL;
  59
  60   SevEsData = (SEV_ES_PER_CPU_DATA *)(Ghcb + 1);
  61   SevEsData->VcCount++;
  62
  63   //
  64   // Check for maximum PEI/DXE #VC nesting.
  65   //
  66   if (SevEsData->VcCount > VMGEXIT_MAXIMUM_VC_COUNT) {
  67     VmgExitIssueAssert (SevEsData);
  68   } else if (SevEsData->VcCount > 1) {
  69     //
  70     // Nested #VC
  71     //
  72     if (SevEsData->GhcbBackupPages == NULL) {
  73       VmgExitIssueAssert (SevEsData);
  74     }
  75
  76     //
  77     // Save the active GHCB to a backup page.
  78     //   To access the correct backup page, increment the backup page pointer
  79     //   based on the current VcCount.
  80     //
  81     GhcbBackup  = (GHCB *)SevEsData->GhcbBackupPages;
  82     GhcbBackup += (SevEsData->VcCount - 2);
  83
  84     CopyMem (GhcbBackup, Ghcb, sizeof (*Ghcb));
  85   }
  86
  87   VcRet = InternalVmgExitHandleVc (Ghcb, ExceptionType, SystemContext);
  88
  89   if (GhcbBackup != NULL) {
  90     //
  91     // Restore the active GHCB from the backup page.
  92     //
  93     CopyMem (Ghcb, GhcbBackup, sizeof (*Ghcb));
  94   }
  95
  96   SevEsData->VcCount--;
  97
  98   if (InterruptState) {
  99     EnableInterrupts ();
 100   }
 101
 102   return VcRet;
 103 }