From 6587e08d3a618facf69da6515ce0dd918d1464ea Mon Sep 17 00:00:00 2001
From: Tom Lendacky <thomas.lendacky@amd.com>
Date: Wed, 12 Aug 2020 15:21:37 -0500
Subject: [PATCH] OvmfPkg/VmgExitLib: Add support for CPUID NAE events

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

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

Add support to construct the required GHCB values to support a CPUID NAE
event. Additionally, CPUID 0x0000_000d (CPUID_EXTENDED_STATE) requires
XCR0 to be supplied in the GHCB, so add support to issue the XGETBV
instruction.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c | 60 +++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
index bc2e270a7c..476e94ce5f 100644
--- a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
+++ b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
@@ -11,6 +11,7 @@
 #include <Library/BaseMemoryLib.h>
 #include <Library/VmgExitLib.h>
 #include <Register/Amd/Msr.h>
+#include <Register/Intel/Cpuid.h>
 #include <IndustryStandard/InstructionParsing.h>
 
 //
@@ -597,6 +598,61 @@ IoioExit (
   return 0;
 }
 
+/**
+  Handle a CPUID event.
+
+  Use the VMGEXIT instruction to handle a CPUID 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
+  @return                          New exception value to propagate
+
+**/
+STATIC
+UINT64
+CpuidExit (
+  IN OUT GHCB                     *Ghcb,
+  IN OUT EFI_SYSTEM_CONTEXT_X64   *Regs,
+  IN     SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  UINT64  Status;
+
+  Ghcb->SaveArea.Rax = Regs->Rax;
+  GhcbSetRegValid (Ghcb, GhcbRax);
+  Ghcb->SaveArea.Rcx = Regs->Rcx;
+  GhcbSetRegValid (Ghcb, GhcbRcx);
+  if (Regs->Rax == CPUID_EXTENDED_STATE) {
+    IA32_CR4  Cr4;
+
+    Cr4.UintN = AsmReadCr4 ();
+    Ghcb->SaveArea.XCr0 = (Cr4.Bits.OSXSAVE == 1) ? AsmXGetBv (0) : 1;
+    GhcbSetRegValid (Ghcb, GhcbXCr0);
+  }
+
+  Status = VmgExit (Ghcb, SVM_EXIT_CPUID, 0, 0);
+  if (Status != 0) {
+    return Status;
+  }
+
+  if (!GhcbIsRegValid (Ghcb, GhcbRax) ||
+      !GhcbIsRegValid (Ghcb, GhcbRbx) ||
+      !GhcbIsRegValid (Ghcb, GhcbRcx) ||
+      !GhcbIsRegValid (Ghcb, GhcbRdx)) {
+    return UnsupportedExit (Ghcb, Regs, InstructionData);
+  }
+  Regs->Rax = Ghcb->SaveArea.Rax;
+  Regs->Rbx = Ghcb->SaveArea.Rbx;
+  Regs->Rcx = Ghcb->SaveArea.Rcx;
+  Regs->Rdx = Ghcb->SaveArea.Rdx;
+
+  return 0;
+}
+
 /**
   Handle a #VC exception.
 
@@ -641,6 +697,10 @@ VmgExitHandleVc (
 
   ExitCode = Regs->ExceptionData;
   switch (ExitCode) {
+  case SVM_EXIT_CPUID:
+    NaeExit = CpuidExit;
+    break;
+
   case SVM_EXIT_IOIO_PROT:
     NaeExit = IoioExit;
     break;