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Re: [PATCH v3 0/4] x86: Drop cross-vendor support
- To: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 11 Mar 2026 11:11:07 +0100
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- Cc: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Community Manager <community.manager@xxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 11 Mar 2026 10:11:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 11.03.2026 10:46, Alejandro Vallejo wrote:
> 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.
>
> 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.
Well, yes, hence the question. Or in other words: Do we consider completeness
important for these insns? (There are others we don't currently support.)
> If not,
> the question is what to do otherwise. Inject #UD? Crash the domain?
#UD is what I think we inject for anything the emulator can't handle.
Jan
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