Re: [Xen-devel] [PATCH 10/24] xen: mask XSAVE from cpuid

Jeremy Fitzhardinge
2009-03-16T00:05:43Z

Arjan van de Ven wrote:
> This is indicative of something that might be a huge bug in Xen:
> Xen should never ever pass through CPUID bits it does not know.
> If Xen does not honor that, there is a fundamental and eternally
> recurring problem.... every time something new gets introduced Xen
> likely breaks.

Yes, I'd agree; Xen should whitelist cpu capabilities rather than
blacklist them. Jan expressed the opposite opinion (on the grounds that
it precludes using features which don't require special OS or hypervisor
support without Xen modifications). But if its just a matter of
sticking a bit into a mask, its easy and quick to roll a new version of
Xen (esp since it can generally be done before CPUs with the new feature
get into people's hands).

J