[RFC PATCH 21/28] UefiCpuPkg/CpuExceptionHandler: Add support for RDTSCP NAE events

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

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

Under SEV-ES, a RDTSCP 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                      | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
index 1a0a8f5cd718..8f9b742f942c 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
@@ -546,6 +546,36 @@ WbinvdExit (
   return 0;
 }
 
+STATIC
+UINTN
+RdtscpExit (
+  GHCB                     *Ghcb,
+  EFI_SYSTEM_CONTEXT_X64   *Regs,
+  SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  UINTN  Status;
+
+  DecodeModRm (Regs, InstructionData);
+
+  Status = VmgExit (Ghcb, SvmExitRdtscp, 0, 0);
+  if (Status) {
+    return Status;
+  }
+
+  if (!GhcbIsRegValid (Ghcb, GhcbRax) ||
+      !GhcbIsRegValid (Ghcb, GhcbRcx) ||
+      !GhcbIsRegValid (Ghcb, GhcbRdx)) {
+    VmgExit (Ghcb, SvmExitUnsupported, SvmExitRdtscp, 0);
+    ASSERT (0);
+  }
+  Regs->Rax = Ghcb->SaveArea.Rax;
+  Regs->Rcx = Ghcb->SaveArea.Rcx;
+  Regs->Rdx = Ghcb->SaveArea.Rdx;
+
+  return 0;
+}
+
 STATIC
 UINTN
 VmmCallExit (
@@ -1005,6 +1035,10 @@ DoVcCommon (
     NaeExit = VmmCallExit;
     break;
 
+  case SvmExitRdtscp:
+    NaeExit = RdtscpExit;
+    break;
+
   case SvmExitWbinvd:
     NaeExit = WbinvdExit;
     break;
-- 
2.17.1