Re: [edk2-devel] [PATCH 2/3] OvmfPkg/VmgExitLib: Add support for new MMIO MOV opcodes

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

On 4/23/21 4:10 AM, Laszlo Ersek wrote:
> On 04/22/21 17:42, Tom Lendacky wrote:
>> On 4/22/21 9:15 AM, Tom Lendacky wrote:
>>> On 4/22/21 12:50 AM, Laszlo Ersek via groups.io wrote:
>>>> On 04/21/21 00:54, Lendacky, Thomas wrote:
>>>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>>>>
>>>>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3345&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Ca0ff778cdbb146a6186508d90637ba60%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637547658699539157%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=vMmmGGXXT8MtM4WOB4gkwtkr0cwwkx98LoOXYg6fclQ%3D&amp;reserved=0
>>>>>
>>>>> Enabling TPM support results in guest termination of an SEV-ES guest
>>>>> because it uses MMIO opcodes that are not currently supported.
>>>>>
>>>>> Add support for the new MMIO opcodes (0xA0 - 0xA3), MOV instructions which
>>>>> use a memory offset directly encoded in the instruction. Also, add a DEBUG
>>>>> statement to identify an unsupported MMIO opcode being used.
>>>>>
>>>>> Fixes: c45f678a1ea2080344e125dc55b14e4b9f98483d
>>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>>>>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>>>>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>>>>> Cc: James Bottomley <jejb@linux.ibm.com>
>>>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>>>> Cc: Min Xu <min.m.xu@intel.com>
>>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>>>> ---
>>>>>  OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c | 99 +++++++++++++++++++
>>>>>  1 file changed, 99 insertions(+)
>>>>>
>>>>> diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
>>>>> index 273f36499988..f9660b757d8e 100644
>>>>> --- a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
>>>>> +++ b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
>>>>> @@ -678,6 +678,7 @@ MmioExit (
>>>>>    UINTN   Bytes;
>>>>>    UINT64  *Register;
>>>>>    UINT8   OpCode, SignByte;
>>>>> +  UINTN   Address;
>>>>>
>>>>>    Bytes = 0;
>>>>>
>>>>> @@ -727,6 +728,51 @@ MmioExit (
>>>>>      }
>>>>>      break;
>>>>>
>>>>> +  //
>>>>> +  // MMIO write (MOV moffsetX, aX)
>>>>> +  //
>>>>> +  case 0xA2:
>>>>> +    Bytes = 1;
>>>>> +    //
>>>>> +    // fall through
>>>>> +    //
>>>>> +  case 0xA3:
>>>>> +    Bytes = ((Bytes != 0) ? Bytes :
>>>>> +             (InstructionData->DataSize == Size16Bits) ? 2 :
>>>>> +             (InstructionData->DataSize == Size32Bits) ? 4 :
>>>>> +             (InstructionData->DataSize == Size64Bits) ? 8 :
>>>>> +             0);
>>>>> +
>>>>> +    InstructionData->ImmediateSize = (UINTN) (1 << InstructionData->AddrSize);
>>>>> +    InstructionData->End += (UINTN) (1 << InstructionData->AddrSize);
>>>>> +
>>>>> +    if (InstructionData->AddrSize == Size8Bits) {
>>>>> +      Address = *(UINT8 *) InstructionData->Immediate;
>>>>> +    } else if (InstructionData->AddrSize == Size16Bits) {
>>>>> +      Address = *(UINT16 *) InstructionData->Immediate;
>>>>> +    } else if (InstructionData->AddrSize == Size32Bits) {
>>>>> +      Address = *(UINT32 *) InstructionData->Immediate;
>>>>> +    } else {
>>>>> +      Address = *(UINTN *) InstructionData->Immediate;
>>>>> +    }
>>>>
>>>> (1) Can we simplify this as follows?
>>>>
>>>>     InstructionData->ImmediateSize = 1 << InstructionData->AddrSize;
>>>>     InstructionData->End += InstructionData->ImmediateSize;
>>>>     Address = 0;
>>>>     CopyMem (&Address, InstructionData->Immediate,
>>>>       InstructionData->ImmediateSize);
>>>
>>> Yup, that can be done.
>>
>> "Address" is a type UINTN, but since this is X64 only code, an 8-byte copy
>> isn't an issue. Should I add a comment about that above the setting of
>> "Address"? Or should I convert "Address" to a UINT64 - although
>> ValidateMmioMemory expects a UINTN...  Thoughts?
> 
> Yes, I had the exact same thought process :)
> 
> The comment looks good, but how about expressing it as a STATIC_ASSERT,
> with sizeof (UINTN) and sizeof (UINT64) being equal? (Alternatively,
> about MAX_UINT64 being equal to MAX_UINTN.)

I like the STATIC_ASSERT idea, I'll do that.

Thanks,
Tom

> 
> If you find that too verbose, a comment is good enough too, of course.
> 
> Thanks!
> Laszlo
> 
>>
>> Thanks,
>> Tom
>>
>>>
>>>>
>>>>> +
>>>>> +    Status = ValidateMmioMemory (Ghcb, Address, Bytes);
>>>>> +    if (Status != 0) {
>>>>> +      return Status;
>>>>> +    }
>>>>> +
>>>>> +    ExitInfo1 = Address;
>>>>> +    ExitInfo2 = Bytes;
>>>>> +    CopyMem (Ghcb->SharedBuffer, &Regs->Rax, Bytes);
>>>>> +
>>>>> +    Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
>>>>> +    VmgSetOffsetValid (Ghcb, GhcbSwScratch);
>>>>> +    Status = VmgExit (Ghcb, SVM_EXIT_MMIO_WRITE, ExitInfo1, ExitInfo2);
>>>>> +    if (Status != 0) {
>>>>> +      return Status;
>>>>> +    }
>>>>> +    break;
>>>>> +
>>>>>    //
>>>>>    // MMIO write (MOV reg/memX, immX)
>>>>>    //
>>>>> @@ -809,6 +855,58 @@ MmioExit (
>>>>>      CopyMem (Register, Ghcb->SharedBuffer, Bytes);
>>>>>      break;
>>>>>
>>>>> +  //
>>>>> +  // MMIO read (MOV aX, moffsetX)
>>>>> +  //
>>>>> +  case 0xA0:
>>>>> +    Bytes = 1;
>>>>> +    //
>>>>> +    // fall through
>>>>> +    //
>>>>> +  case 0xA1:
>>>>> +    Bytes = ((Bytes != 0) ? Bytes :
>>>>> +             (InstructionData->DataSize == Size16Bits) ? 2 :
>>>>> +             (InstructionData->DataSize == Size32Bits) ? 4 :
>>>>> +             (InstructionData->DataSize == Size64Bits) ? 8 :
>>>>> +             0);
>>>>> +
>>>>> +    InstructionData->ImmediateSize = (UINTN) (1 << InstructionData->AddrSize);
>>>>> +    InstructionData->End += (UINTN) (1 << InstructionData->AddrSize);
>>>>> +
>>>>> +    if (InstructionData->AddrSize == Size8Bits) {
>>>>> +      Address = *(UINT8 *) InstructionData->Immediate;
>>>>> +    } else if (InstructionData->AddrSize == Size16Bits) {
>>>>> +      Address = *(UINT16 *) InstructionData->Immediate;
>>>>> +    } else if (InstructionData->AddrSize == Size32Bits) {
>>>>> +      Address = *(UINT32 *) InstructionData->Immediate;
>>>>> +    } else {
>>>>> +      Address = *(UINTN *) InstructionData->Immediate;
>>>>> +    }
>>>>
>>>> (2) Similar question as (1).
>>>
>>> Will do.
>>>
>>>>
>>>>> +
>>>>> +    Status = ValidateMmioMemory (Ghcb, Address, Bytes);
>>>>> +    if (Status != 0) {
>>>>> +      return Status;
>>>>> +    }
>>>>> +
>>>>> +    ExitInfo1 = Address;
>>>>> +    ExitInfo2 = Bytes;
>>>>> +
>>>>> +    Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
>>>>> +    VmgSetOffsetValid (Ghcb, GhcbSwScratch);
>>>>> +    Status = VmgExit (Ghcb, SVM_EXIT_MMIO_READ, ExitInfo1, ExitInfo2);
>>>>> +    if (Status != 0) {
>>>>> +      return Status;
>>>>> +    }
>>>>> +
>>>>> +    if (Bytes == 4) {
>>>>> +      //
>>>>> +      // Zero-extend for 32-bit operation
>>>>> +      //
>>>>> +      Regs->Rax = 0;
>>>>> +    }
>>>>
>>>> (3) This is also seen with opcode 0x8B, but can you remind me please why
>>>> we ignore (Bytes == 1) and (Bytes == 2) for zero extension?
>>>
>>> That comes from the APM Vol 3, Table B-1, that says, in 64-bit mode, for a
>>> 32-bit operand size the 32-bit register results are zero-extended to 64-bits.
>>>
>>>>
>>>>> +    CopyMem (&Regs->Rax, Ghcb->SharedBuffer, Bytes);
>>>>> +    break;
>>>>> +
>>>>>    //
>>>>>    // MMIO read w/ zero-extension ((MOVZX regX, reg/memX)
>>>>>    //
>>>>> @@ -886,6 +984,7 @@ MmioExit (
>>>>>      break;
>>>>>
>>>>>    default:
>>>>> +    DEBUG ((DEBUG_INFO, "Invalid MMIO opcode (%x)\n", OpCode));
>>>>>      Status = GP_EXCEPTION;
>>>>>      ASSERT (FALSE);
>>>>>    }
>>>>>
>>>>
>>>> (4) We should use the DEBUG_ERROR log mask here.
>>>
>>> Will change.
>>>
>>> Thanks,
>>> Tom
>>>
>>>>
>>>> Thanks
>>>> Laszlo
>>>>
>>>>
>>>>
>>>> 
>>>>
>>>>
>>
>