[RFC PATCH 15/28] UefiCpuPkg/CpuExceptionHandler: Add support for NPF NAE events (MMIO)

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

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

Under SEV-ES, a NPF intercept for an NPT entry with a reserved bit set
generates a #VC exception. This condition is assumed to be an MMIO access.
VMGEXIT must be used to allow the hypervisor to handle this intercept.

Add support to construct the required GHCB values to support a NPF NAE
event for MMIO.  Parse the instruction that generated the #VC exception,
setting the required register values in the GHCB and creating the proper
SW_EXIT_INFO1, SW_EXITINFO2 and SW_SCRATCH values in the GHCB.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 .../X64/AMDSevVcCommon.c                      | 285 +++++++++++++++++-
 1 file changed, 283 insertions(+), 2 deletions(-)

diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
index 2b25919ea496..5b2df92acf72 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/AMDSevVcCommon.c
@@ -78,8 +78,8 @@ typedef struct {
     UINT8  Scale;
   } Sib;
 
-  UINTN  RegData;
-  UINTN  RmData;
+  INTN  RegData;
+  INTN  RmData;
 } SEV_ES_INSTRUCTION_OPCODE_EXT;
 
 typedef struct {
@@ -124,6 +124,198 @@ UINTN
   SEV_ES_INSTRUCTION_DATA  *InstructionData
   );
 
+STATIC
+INT64 *
+GetRegisterPointer (
+  EFI_SYSTEM_CONTEXT_X64   *Regs,
+  UINT8                    Register
+  )
+{
+  UINT64 *Reg;
+
+  switch (Register) {
+  case 0:
+    Reg = &Regs->Rax;
+    break;
+  case 1:
+    Reg = &Regs->Rcx;
+    break;
+  case 2:
+    Reg = &Regs->Rdx;
+    break;
+  case 3:
+    Reg = &Regs->Rbx;
+    break;
+  case 4:
+    Reg = &Regs->Rsp;
+    break;
+  case 5:
+    Reg = &Regs->Rbp;
+    break;
+  case 6:
+    Reg = &Regs->Rsi;
+    break;
+  case 7:
+    Reg = &Regs->Rdi;
+    break;
+  case 8:
+    Reg = &Regs->R8;
+    break;
+  case 9:
+    Reg = &Regs->R9;
+    break;
+  case 10:
+    Reg = &Regs->R10;
+    break;
+  case 11:
+    Reg = &Regs->R11;
+    break;
+  case 12:
+    Reg = &Regs->R12;
+    break;
+  case 13:
+    Reg = &Regs->R13;
+    break;
+  case 14:
+    Reg = &Regs->R14;
+    break;
+  case 15:
+    Reg = &Regs->R15;
+    break;
+  default:
+    Reg = NULL;
+  }
+  ASSERT (Reg);
+
+  return (INT64 *) Reg;
+}
+
+STATIC
+VOID
+UpdateForDisplacement (
+  SEV_ES_INSTRUCTION_DATA  *InstructionData,
+  UINTN                    Size
+  )
+{
+  InstructionData->DisplacementSize = Size;
+  InstructionData->Immediate += Size;
+  InstructionData->End += Size;
+}
+
+STATIC
+BOOLEAN
+IsRipRelative (
+  SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  SEV_ES_INSTRUCTION_OPCODE_EXT  *Ext = &InstructionData->Ext;
+
+  return ((InstructionData == LongMode64Bit) &&
+          (Ext->ModRm.Mod == 0) &&
+          (Ext->ModRm.Rm == 5)  &&
+          (InstructionData->SibPresent == FALSE));
+}
+
+STATIC
+UINTN
+GetEffectiveMemoryAddress (
+  EFI_SYSTEM_CONTEXT_X64   *Regs,
+  SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  SEV_ES_INSTRUCTION_OPCODE_EXT  *Ext = &InstructionData->Ext;
+  INTN                           EffectiveAddress = 0;
+
+  if (IsRipRelative (InstructionData)) {
+    /* RIP-relative displacement is a 32-bit signed value */
+    INT32 RipRelative = *(INT32 *) InstructionData->Displacement;
+
+    UpdateForDisplacement (InstructionData, 4);
+    return (UINTN) ((INTN) Regs->Rip + RipRelative);
+  }
+
+  switch (Ext->ModRm.Mod) {
+  case 1:
+    UpdateForDisplacement (InstructionData, 1);
+    EffectiveAddress += (INT8) (*(INT8 *) (InstructionData->Displacement));
+    break;
+  case 2:
+    switch (InstructionData->AddrSize) {
+    case Size16Bits:
+      UpdateForDisplacement (InstructionData, 2);
+      EffectiveAddress += (INT16) (*(INT16 *) (InstructionData->Displacement));
+      break;
+    default:
+      UpdateForDisplacement (InstructionData, 4);
+      EffectiveAddress += (INT32) (*(INT32 *) (InstructionData->Displacement));
+      break;
+    }
+    break;
+  }
+
+  if (InstructionData->SibPresent) {
+    if (Ext->Sib.Index != 4) {
+      EffectiveAddress += (*GetRegisterPointer (Regs, Ext->Sib.Index) << Ext->Sib.Scale);
+    }
+
+    if ((Ext->Sib.Base != 5) || Ext->ModRm.Mod) {
+      EffectiveAddress += *GetRegisterPointer (Regs, Ext->Sib.Base);
+    } else {
+      UpdateForDisplacement (InstructionData, 4);
+      EffectiveAddress += (INT32) (*(INT32 *) (InstructionData->Displacement));
+    }
+  } else {
+    EffectiveAddress += *GetRegisterPointer (Regs, Ext->ModRm.Rm);
+  }
+
+  return (UINTN) EffectiveAddress;
+}
+
+STATIC
+VOID
+DecodeModRm (
+  EFI_SYSTEM_CONTEXT_X64   *Regs,
+  SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  SEV_ES_INSTRUCTION_REX_PREFIX  *RexPrefix = &InstructionData->RexPrefix;
+  SEV_ES_INSTRUCTION_OPCODE_EXT  *Ext = &InstructionData->Ext;
+  SEV_ES_INSTRUCTION_MODRM       *ModRm = &InstructionData->ModRm;
+  SEV_ES_INSTRUCTION_SIB         *Sib = &InstructionData->Sib;
+
+  InstructionData->ModRmPresent = TRUE;
+  ModRm->Uint8 = *(InstructionData->End);
+
+  InstructionData->Displacement++;
+  InstructionData->Immediate++;
+  InstructionData->End++;
+
+  Ext->ModRm.Mod = ModRm->Bits.Mod;
+  Ext->ModRm.Reg = (RexPrefix->Bits.R << 3) | ModRm->Bits.Reg;
+  Ext->ModRm.Rm  = (RexPrefix->Bits.B << 3) | ModRm->Bits.Rm;
+
+  Ext->RegData = *GetRegisterPointer (Regs, Ext->ModRm.Reg);
+
+  if (Ext->ModRm.Mod == 3) {
+    Ext->RmData = *GetRegisterPointer (Regs, Ext->ModRm.Rm);
+  } else {
+    if (ModRm->Bits.Rm == 4) {
+      InstructionData->SibPresent = TRUE;
+      Sib->Uint8 = *(InstructionData->End);
+
+      InstructionData->Displacement++;
+      InstructionData->Immediate++;
+      InstructionData->End++;
+
+      Ext->Sib.Scale = Sib->Bits.Scale;
+      Ext->Sib.Index = (RexPrefix->Bits.X << 3) | Sib->Bits.Index;
+      Ext->Sib.Base  = (RexPrefix->Bits.B << 3) | Sib->Bits.Base;
+    }
+
+    Ext->RmData = GetEffectiveMemoryAddress (Regs, InstructionData);
+  }
+}
+
 STATIC
 VOID
 DecodePrefixes (
@@ -235,6 +427,91 @@ InitInstructionData (
   DecodePrefixes (Regs, InstructionData);
 }
 
+STATIC
+UINT64
+MmioExit (
+  GHCB                     *Ghcb,
+  EFI_SYSTEM_CONTEXT_X64   *Regs,
+  SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  UINT64  ExitInfo1, ExitInfo2;
+  UINTN   Status;
+  UINTN   Bytes;
+  INTN    *Register;
+
+  Bytes = 0;
+
+  switch (*(InstructionData->OpCodes)) {
+  /* MMIO write */
+  case 0x88:
+    Bytes = 1;
+  case 0x89:
+    DecodeModRm (Regs, InstructionData);
+    Bytes = (Bytes) ? Bytes
+                    : (InstructionData->DataSize == Size16Bits) ? 2
+                    : (InstructionData->DataSize == Size32Bits) ? 4
+                    : (InstructionData->DataSize == Size64Bits) ? 8
+                    : 0;
+
+    if (InstructionData->Ext.ModRm.Mod == 3) {
+      /* NPF on two register operands??? */
+      VmgExit (Ghcb, SvmExitUnsupported, SvmExitNpf, 0);
+      ASSERT (0);
+    }
+
+    ExitInfo1 = InstructionData->Ext.RmData;
+    ExitInfo2 = Bytes;
+    CopyMem (Ghcb->SharedBuffer, &InstructionData->Ext.RegData, Bytes);
+
+    Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
+    Status = VmgExit (Ghcb, SvmExitMmioWrite, ExitInfo1, ExitInfo2);
+    if (Status) {
+      return Status;
+    }
+    break;
+
+  /* MMIO read */
+  case 0x8A:
+    Bytes = 1;
+  case 0x8B:
+    DecodeModRm (Regs, InstructionData);
+    Bytes = (Bytes) ? Bytes
+                    : (InstructionData->DataSize == Size16Bits) ? 2
+                    : (InstructionData->DataSize == Size32Bits) ? 4
+                    : (InstructionData->DataSize == Size64Bits) ? 8
+                    : 0;
+    if (InstructionData->Ext.ModRm.Mod == 3) {
+      /* NPF on two register operands??? */
+      VmgExit (Ghcb, SvmExitUnsupported, SvmExitNpf, 0);
+      ASSERT (0);
+    }
+
+    ExitInfo1 = InstructionData->Ext.RmData;
+    ExitInfo2 = Bytes;
+
+    Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
+    Status = VmgExit (Ghcb, SvmExitMmioRead, ExitInfo1, ExitInfo2);
+    if (Status) {
+      return Status;
+    }
+
+    Register = GetRegisterPointer (Regs, InstructionData->Ext.ModRm.Reg);
+    if (Bytes == 4) {
+      /* Zero-extend for 32-bit operation */
+      *Register = 0;
+    }
+    CopyMem (Register, Ghcb->SharedBuffer, Bytes);
+    break;
+
+  default:
+    Status = GP_EXCEPTION;
+    ASSERT (0);
+  }
+
+  return Status;
+}
+
 STATIC
 UINTN
 UnsupportedExit (
@@ -590,6 +867,10 @@ DoVcCommon (
     NaeExit = MsrExit;
     break;
 
+  case SvmExitNpf:
+    NaeExit = MmioExit;
+    break;
+
   default:
     NaeExit = UnsupportedExit;
   }
-- 
2.17.1