[PATCH v8 19/46] OvmfPkg/VmgExitLib: Add support for RDTSC NAE events

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

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198

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

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 .../Library/VmgExitLib/X64/VmgExitVcHandler.c | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/OvmfPkg/Library/VmgExitLib/X64/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/X64/VmgExitVcHandler.c
index 0cf26c052b32..3d2a9c6f9bc9 100644
--- a/OvmfPkg/Library/VmgExitLib/X64/VmgExitVcHandler.c
+++ b/OvmfPkg/Library/VmgExitLib/X64/VmgExitVcHandler.c
@@ -1214,6 +1214,45 @@ CpuidExit (
   return 0;
 }
 
+/**
+  Handle a RDTSC event.
+
+  Use the VMGEXIT instruction to handle a RDTSC event.
+
+  @param[in, out] Ghcb             Pointer to the Guest-Hypervisor Communication
+                                   Block
+  @param[in, out] Regs             x64 processor context
+  @param[in]      InstructionData  Instruction parsing context
+
+  @retval 0                        Event handled successfully
+  @retval Others                   New exception value to propagate
+
+**/
+STATIC
+UINT64
+RdtscExit (
+  IN OUT GHCB                     *Ghcb,
+  IN OUT EFI_SYSTEM_CONTEXT_X64   *Regs,
+  IN     SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  UINT64  Status;
+
+  Status = VmgExit (Ghcb, SVM_EXIT_RDTSC, 0, 0);
+  if (Status) {
+    return Status;
+  }
+
+  if (!GhcbIsRegValid (Ghcb, GhcbRax) ||
+      !GhcbIsRegValid (Ghcb, GhcbRdx)) {
+    return UnsupportedExit (Ghcb, Regs, InstructionData);
+  }
+  Regs->Rax = Ghcb->SaveArea.Rax;
+  Regs->Rdx = Ghcb->SaveArea.Rdx;
+
+  return 0;
+}
+
 /**
   Handle a #VC exception.
 
@@ -1258,6 +1297,10 @@ VmgExitHandleVc (
 
   ExitCode = Regs->ExceptionData;
   switch (ExitCode) {
+  case SVM_EXIT_RDTSC:
+    NaeExit = RdtscExit;
+    break;
+
   case SVM_EXIT_CPUID:
     NaeExit = CpuidExit;
     break;
-- 
2.17.1