Re: [PATCH 2/9] OvmfPkg/VmgExitLib: Set the SW exit fields when performing VMGEXIT

["Laszlo Ersek" <lersek@redhat.com>]

On 10/15/20 10:47, Laszlo Ersek wrote:
> On 10/10/20 18:07, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> All fields that are set in the GHCB should have their associated bit in
>> the GHCB ValidBitmap field set. Add support to set the bits for the
>> software exit information fields when performing a VMGEXIT (SwExitCode,
>> SwExitInfo1, SwExitInfo2).
>>
>> Fixes: 61bacc0fa16f ("OvmfPkg/VmgExitLib: Implement library support for VmgExitLib in OVMF")
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  OvmfPkg/Library/VmgExitLib/VmgExitLib.c | 30 ++++++++++++++++++++
>>  1 file changed, 30 insertions(+)
>>
>> diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitLib.c b/OvmfPkg/Library/VmgExitLib/VmgExitLib.c
>> index 53040cc6f649..6cf649c6101b 100644
>> --- a/OvmfPkg/Library/VmgExitLib/VmgExitLib.c
>> +++ b/OvmfPkg/Library/VmgExitLib/VmgExitLib.c
>> @@ -78,6 +78,32 @@ VmgExitErrorCheck (
>>    return Status;
>>  }
>>  
>> +/**
>> +  Marks a field at the specified offset as valid in the GHCB.
>> +
>> +  The ValidBitmap area represents the areas of the GHCB that have been marked
>> +  valid. Set the area of the GHCB at the specified offset as valid.
>> +
>> +  @param[in, out] Ghcb    Pointer to the Guest-Hypervisor Communication Block
>> +  @param[in] Offset       Offset in the GHCB to mark valid
>> +
>> +**/
>> +STATIC
>> +VOID
>> +GhcbSetOffsetValid (
>> +  IN OUT GHCB               *Ghcb,
>> +  IN     GHCB_QWORD_OFFSET  Offset
>> +  )
>> +{
>> +  UINT32  OffsetIndex;
>> +  UINT32  OffsetBit;
>> +
>> +  OffsetIndex = Offset / 8;
>> +  OffsetBit   = Offset & 0x07;
> 
> (1) I suggest improving the consistency of operators -- please either
> use division and remainder ("Offset / 8" and "Offset % 8"), or bit shift
> and masking ("Offset >> 3" and "Offset & 0x7")
> 
> With that:
> 
> Acked-by: Laszlo Ersek <lersek@redhat.com>

... I realize I didn't make the same comment for GhcbIsRegValid(), so
I'm taking back the above -- consistency with GhcbIsRegValid() is more
important. No change needed here.

Acked-by: Laszlo Ersek <lersek@redhat.com>

Thanks,
Laszlo

> 
> Thanks
> Laszlo
> 
>> +
>> +  Ghcb->SaveArea.ValidBitmap[OffsetIndex] |= (1 << OffsetBit);
>> +}
>> +
>>  /**
>>    Perform VMGEXIT.
>>  
>> @@ -110,6 +136,10 @@ VmgExit (
>>    Ghcb->SaveArea.SwExitInfo1 = ExitInfo1;
>>    Ghcb->SaveArea.SwExitInfo2 = ExitInfo2;
>>  
>> +  GhcbSetOffsetValid (Ghcb, GhcbSwExitCode);
>> +  GhcbSetOffsetValid (Ghcb, GhcbSwExitInfo1);
>> +  GhcbSetOffsetValid (Ghcb, GhcbSwExitInfo2);
>> +
>>    //
>>    // Guest memory is used for the guest-hypervisor communication, so fence
>>    // the invocation of the VMGEXIT instruction to ensure GHCB accesses are
>>
>