[RFC PATCH 22/28] UefiCpuPkg/CpuExceptionHandler: Add support for MONITOR/MONITORX NAE events

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

From: Tom Lendacky <thomas.lendacky@amd.com>

Under SEV-ES, a MONITOR/MONITORX intercept generates a #VC exception.
VMGEXIT must be used to allow the hypervisor to handle this intercept.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 .../X64/AMDSevVcCommon.c                      | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
index 8f9b742f942c..154ca091936d 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
@@ -528,6 +528,33 @@ UnsupportedExit (
   return Status;
 }
 
+STATIC
+UINTN
+MonitorExit (
+  GHCB                     *Ghcb,
+  EFI_SYSTEM_CONTEXT_X64   *Regs,
+  SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  UINTN   Status;
+
+  DecodeModRm (Regs, InstructionData);
+
+  Ghcb->SaveArea.Rax = Regs->Rax;  // Identity mapped, so VA = PA
+  GhcbSetRegValid (Ghcb, GhcbRax);
+  Ghcb->SaveArea.Rcx = Regs->Rcx;
+  GhcbSetRegValid (Ghcb, GhcbRcx);
+  Ghcb->SaveArea.Rdx = Regs->Rdx;
+  GhcbSetRegValid (Ghcb, GhcbRdx);
+
+  Status = VmgExit (Ghcb, SvmExitMonitor, 0, 0);
+  if (Status) {
+    return Status;
+  }
+
+  return 0;
+}
+
 STATIC
 UINTN
 WbinvdExit (
@@ -1043,6 +1070,10 @@ DoVcCommon (
     NaeExit = WbinvdExit;
     break;
 
+  case SvmExitMonitor:
+    NaeExit = MonitorExit;
+    break;
+
   case SvmExitNpf:
     NaeExit = MmioExit;
     break;
-- 
2.17.1