Re: [Qemu-devel] allow sysenter on 32bit guests running on vmx host

[Andrea Arcangeli <aarcange@redhat.com>]

On Wed, Jun 24, 2009 at 07:48:55PM +0200, Filip Navara wrote:
> On Wed, Jun 24, 2009 at 7:29 PM, Jamie Lokier <jamie@shareable.org> wrote:
> [snip]
> >
> > > Fix is to set model = 3 so it'll be the duron cpu when kvm runs on
> > > amd bare metal (not anymore athlon but userland doesn't see the
> > > difference) and it'll be PII that has sysenter functional like all
> > > cpus that run KVM have too when on intel bare metal.
> >
> > But the vendor id is AMD not Intel in this structure, and the PPro
> > workaround is Intel-only.
> >
> > I've checked Linux kernel code, and it only disables the sep feature
> > if the vendor is GenuineIntel, on old and current kernels.
> >
> > So your patch should make no difference to Linux guests.  Did you
> > check Linux behaviour?  Does Windows ignore the vendor id?
> 
> 
> No, it doesn't ignore the vendor, at least not on NT 5.2 (Windows Server
> 2003) and newer kernels. I'm pretty sure it wasn't ignored even in Windows
> XP, older systems didn't implement it.

Correct, not only windows, skype also doesn't ignore the vendor and
it doesn't attempt to run sysenter if running KVM on amd host (or qemu
in any amd/intel host).

skype crashes because windows on intel ignores sep on 6/2/3 (as well
as linux too) and it disables sysenter, but skype runs sysenter in its
binary even on 6/2/3 (tracked with windbg).