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

[Marcelo Tosatti]

On Wed, Apr 30, 2014 at 10:44:33AM +0200, Paolo Bonzini wrote:
> Il 30/04/2014 03:11, Marcelo Tosatti ha scritto:
> > 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 that would break "-cpu ...,enforce".  In fact many old models 
> are currently broken because they were never tested with "-cpu 
> ...,enforce".  For example:

Isnt the point of enforce to fail if the provided feature cannot be
exposed ?

That is, if the emulated CPU specifies MONITOR, and KVM can't provide
it, then enforce should fail initialization?

QEMU/KVM currently filters both in userspace and kernelspace.