Re: [PATCH 0/4] x86: Drop cross-vendor support

[Alejandro Vallejo <alejandro.garciavallejo@amd.com>]

On Thu Jan 22, 2026 at 7:19 PM CET, Andrew Cooper wrote:
> On 22/01/2026 5:42 pm, Alejandro Vallejo wrote:
>> On Thu Jan 22, 2026 at 6:10 PM CET, Andrew Cooper wrote:
>>> On 22/01/2026 4:49 pm, Alejandro Vallejo wrote:
>>>> Open question unrelated to the series: Does it make sense to conditionalise the
>>>> MSR handlers for non intercepted MSRs on HVM_FEP?
>>> I'm not quite sure what you're asking here.
>>>
>>> ~Andrew
>> The handlers for LSTAR and the like are dead code with !CONFIG_HVM_FEP as far
>> as I can tell. The question I'm asking is whether there is another code path
>> that might invoke MSR handlers for non-intercepted MSRs. I can't see it, but
>> I'm not sure.
>>
>> If there isn't I'm considering (conditionally) getting rid of them.
>
> Introspection can (and HVMI does) hook them.  Changes to LSTAR during
> runtime is usually an exploit in progress.
>
> Nested virt also makes it far more complicated to reason about
> "intercepted or not", given that there are multiple opinions merged
> together.
>
> ~Andrew

nSVM definitely would trigger those, ta.

Conditionally removing nSVM is in our roadmap, and VMI is already gated on
ALTP2M. I'll put this on the pile somewhere.

Cheers,
Alejandro