[RFC PATCH 23/28] UefiCpuPkg/CpuExceptionHandler: Add support for MWAIT/MWAITX NAE events

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

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

Under SEV-ES, a MWAIT/MWAITX 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                      | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
index 154ca091936d..43a3a116af5d 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
@@ -528,6 +528,31 @@ UnsupportedExit (
   return Status;
 }
 
+STATIC
+UINTN
+MwaitExit (
+  GHCB                     *Ghcb,
+  EFI_SYSTEM_CONTEXT_X64   *Regs,
+  SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  UINTN   Status;
+
+  DecodeModRm (Regs, InstructionData);
+
+  Ghcb->SaveArea.Rax = Regs->Rax;
+  GhcbSetRegValid (Ghcb, GhcbRax);
+  Ghcb->SaveArea.Rcx = Regs->Rcx;
+  GhcbSetRegValid (Ghcb, GhcbRcx);
+
+  Status = VmgExit (Ghcb, SvmExitMwait, 0, 0);
+  if (Status) {
+    return Status;
+  }
+
+  return 0;
+}
+
 STATIC
 UINTN
 MonitorExit (
@@ -1074,6 +1099,10 @@ DoVcCommon (
     NaeExit = MonitorExit;
     break;
 
+  case SvmExitMwait:
+    NaeExit = MwaitExit;
+    break;
+
   case SvmExitNpf:
     NaeExit = MmioExit;
     break;
-- 
2.17.1