Re: [PATCH] Use WARN_ON_ONCE for missing X86_FEATURE_NRIPS

[Bandan Das <bsd@redhat.com>]

Joerg Roedel <joro@8bytes.org> writes:

> On Mon, Oct 05, 2015 at 01:42:43PM -0400, Bandan Das wrote:
>> Joerg Roedel <joro@8bytes.org> writes:
>> 
>> > On Mon, Oct 05, 2015 at 12:54:43PM -0400, Bandan Das wrote:
>> >> Joerg Roedel <joro@8bytes.org> writes:
>> >> The problems is that the next_rip field could be stale. If the processor supports
>> >> next_rip, then it will clear it out on the next entry. If it doesn't,
>> >> an old value just sits there (no matter who wrote it) and the problem
>> >> happens when skip_emulated_instruction advances the rip with an incorrect
>> >> value.
>> >
>> > So the right fix would be to just set the guests next_rip to 0 when we
>> > emulate vmrun, just like real hardware does, no?
>> 
>> Agreed, resetting to 0 if nrips isn't supported seems right. It would still
>> help having a printk_once in this case IMO :)
>
> I meant to reset it always to 0 on vmrun, like real hardware does.

Atleast the spec don't mention this, I don't know how I got that idea :) The spec
just say that it gets written to by hardware on certain intercepts and for others
it gets reset to 0 on #VMEXIT.

>
>
> 	Joerg