Re: [PATCH v3 0/4] x86: Drop cross-vendor support

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

On Wed Mar 11, 2026 at 9:54 AM CET, Jan Beulich wrote:
> On 13.02.2026 12:42, Alejandro Vallejo wrote:
>> Alejandro Vallejo (4):
>>   x86: Reject CPU policies with vendors other than the host's
>>   x86/hvm: Disable cross-vendor handling in #UD handler
>>   x86/hvm: Remove cross-vendor checks from MSR handlers.
>>   x86/svm: Drop emulation of Intel's SYSENTER behaviour on AMD systems
>
> With this, do we actually want to keep emulation of SYS{ENTER,EXIT,CALL,RET}
> in the insn emulator? Or at least gate that on e.g. VM_EVENT, to still allow
> its use by introspection? Whether to then also permit those with HVM_FEP=y
> (but VM_EVENT=n) would be a follow-on question.
>
> Jan

I can force emulation of anything by writing an instruction to an xAPIC register
followed by RET and then CALL-ing it that address. If we want a hypervisor
capable of running such ridiculous cases the emulator must be complete. If not,
the question is what to do otherwise. Inject #UD? Crash the domain?

Cheers,
Alejandro