Re: [RFC] Expose host cpuid to guest

[Dan Kenigsberg <danken-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

On Thu, Nov 22, 2007 at 10:12:04AM +1030, Mike Lampard wrote:
> On Wed, 21 Nov 2007 09:36:31 pm Dan Kenigsberg wrote:
> > These patches expose host CPU features (that are known to work under
> > KVM) to guests. It makes a couple of benchmarks run faster, and
> > generally gives kvm's user better info on its host.
> >
> > The kernel-space patch adds KVM_GET_SUPPORTED_CPUID ioctl to obtain the
> > table of cpuid functions supported by the host. The user-space patch
> > allows fine-tuning this table from the command-line.
> >
> > I had to define struct kvm_cpuid2, KVM_SET_CPUID2 etc., because cpuid
> > functions are a little more complex than just function-value pairs.
> >
> > Dan.
> 
> With current kvm-git (commit 51727a110220681f6f43b005d069e28c58f5d151) 
> (userspace is current to commit 6a385c9539f9746d7ff51ef34c064c3eba86448b) and 
> the userspace portion of this patch I cannot boot a 64 bit guest (Mandriva 
> 2008 x64) on my AMD x2 without -cpu host.  The guest kernel says "Your CPU 
> does not support long mode.  Use a 32bit distribution.".  Works fine without 
> the userspace portion of the patch.  

Thanks for your report. I'm probably not exposing one(?) of AMD's x86_64
required cpuid features. However, I fail to reproduce this on Dual-Core
AMD Opteron(tm) Processor 2210 running 2.6.18-8.1.15.el5. What is your
host?

Dan.

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