Re: [PATCH v8 04/12] x86emul: support SERIALIZE

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/05/2020 08:34, Jan Beulich wrote:
>>> @@ -5660,6 +5661,18 @@ x86_emulate(
>>>                  goto done;
>>>              break;
>>>  
>>> +        case 0xe8:
>>> +            switch ( vex.pfx )
>>> +            {
>>> +            case vex_none: /* serialize */
>>> +                host_and_vcpu_must_have(serialize);
>>> +                asm volatile ( ".byte 0x0f, 0x01, 0xe8" );
>> There is very little need for an actual implementation here.  The VMExit
>> to get here is good enough.
>>
>> The only question is whether pre-unrestricted_guest Intel boxes are
>> liable to find this in real mode code.
> Apart from this we also shouldn't assume HVM in the core emulator,
> I think.

It's not assuming HVM.  Its just that there is no way we can end up
emulating this instruction from PV context.

If we could end up here in PV context, the exception causing us to
emulate to begin with would be good enough as well.

~Andrew