Re: [PATCH -v2] kvm: Emulate MOVBE

[Borislav Petkov <bp@alien8.de>]

On Tue, Apr 16, 2013 at 08:42:36PM +0300, Gleb Natapov wrote:
> > Right, and this is what we have, AFAICT. And if userspace does that what
> > you exemplify above, you get exactly that - a feature bit not set in
> > CPUID but KVM reporting it set means, it is emulated. There's no room
> > for other interpretations here. Which probably means also not optimal
> > because it is not done in hw.
> > 
> This is not true for all emulated CPUID bits. X2APIC is emulated and it
> is preferable for a guest to use it for example.

Right, and on boxes without X2APIC support you will not find
CPUID(1).ECX[21] set. kvm will tell you it is supported, though, which
means, kvm emulates it.

> > Or, do you want to have a way to say with KVM_GET_SUPPORTED_CPUID that
> > "the features I'm reporting to you are those - a subset of them are not
> > optimally supported because I'm emulating them."
> > 
> > Am I close?
> > 
> Yes, you are. I am considering such interface. Adding new specialized
> interfaces is last resort though. I am open to other ideas.

Hmm, ok, so basically we want qemu to query the host CPUID and see which
features are *really* supported, then do KVM_GET_SUPPORTED_CPUID and see
which are emulated.

How's that? Too simple?

I probably am missing something as a novice qemu user.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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