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

[Paul Brook]

On Thursday 25 June 2009, Andrea Arcangeli wrote:
> On Thu, Jun 25, 2009 at 06:39:19PM +0100, Paul Brook wrote:
> > > What's missing is a comment saying "KVM changes this vendor id to
> > > Intel when run on a VMX-capable host".
> >
> > I don't see how this is anything other than a KVM bug. The user requested
> > an AMD vendor ID. Arbitrarily changing it to something else is just plain
> > wrong.
>
> Oh my, no -cpu is passed on the command line, and by default the only
> thing the user asks is always only one: performance.

I don't buy this. I'd expect a a good proportion of users to care more about 
correct operation over absolute performance. A fast VM is no good if it 
doesn't actually work.

On closer inspection I notice that we use an AMD vendor ID for the "qemu64" 
cpu. IMO this is wrong, we should be using our own ID. However this does not 
change the underlying problem - KVM absolutely should not be unilaterally 
changing the reported vendor ID.  Maybe select a different CPU by default, and 
probably fail to run if the selected CPU ID is incompatible with the host 
hardware features, but not arbitrarily mutate the provided CPUID.

Paul