Re: [Qemu-devel] [PATCH] target-i386: kvm: Don't enable MONITOR by default on any CPU model

[Eduardo Habkost]

On Tue, Apr 29, 2014 at 10:11:08PM -0300, Marcelo Tosatti wrote:
> On Tue, Apr 29, 2014 at 06:17:17PM -0300, Eduardo Habkost wrote:
> > KVM never supported the MONITOR flag so it doesn't make sense to have it
> > enabled by default when KVM is enabled.
> > 
> > The rationale here is similar to the cases where it makes sense to have
> > a feature enabled by default on all CPU models when on KVM mode (e.g.
> > x2apic). In this case we are having a feature disabled by default for
> > the same reasons.
> > 
> > In this case we don't need machine-type compat code because it is
> > currently impossible to run a KVM VM with the MONITOR flag set.
> > 
> > Signed-off-by: Eduardo Habkost <address@hidden>
> 
> Why relying on the kernel filtering is not sufficient ? 

Because:

 * When "enforce" is used, it will prevent a VM from being started
   because the feature is not supported by the kernel.
 * When "enforce" is not used, it breaks the guest ABI when the values
   returned by GET_SUPPORTED_CPUID change.

-- 
Eduardo