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

Andi Kleen
2009-03-17T00:02:26Z

"Jan Beulich" <jbeulich@novell.com> writes:

>>>> Arjan van de Ven <arjan@infradead.org> 16.03.09 01:09 >>>
>>Well.. pretty much all new instructions need Xen modifications due to
>>the need to be emulate to deal with traps/vmexits/etc right?
>>So I don't quite see many cpuid bits that would NOT involve some Xen
>>modification or another ;)
>
> No, new (user-mode accessible) instructions represent precisely the kind
> of extension that do not require hypervisor (or OS) awareness (see SSE2
> etc, AES, FMA). New registers otoh are examples of where awareness is
> needed (SSE, AVX), as would be new privileged instructions.

Whey would another hypothetical FP register extension need Xen support
once it gets proper XSAVE support? I can't think of a reason why
(assuming XSAVE support) it would need to know of a new kind of
FP register or similar. They very likely won't appear in any
instructions that need mmio. Or are you worried about the real
mode emulator?

-Andi

--
ak@linux.intel.com -- Speaking for myself only.