Re: [PATCH 0/2] i386: Fix interrupt based Async PF enablement

[Eduardo Habkost]

On Thu, Apr 15, 2021 at 08:14:30PM +0100, Dr. David Alan Gilbert wrote:
> * Paolo Bonzini (pbonzini@redhat.com) wrote:
> > On 06/04/21 13:42, Vitaly Kuznetsov wrote:
> > > older machine types are still available (I disable it for <= 5.1 but we
> > > can consider disabling it for 5.2 too). The feature is upstream since
> > > Linux 5.8, I know that QEMU supports much older kernels but this doesn't
> > > probably mean that we can't enable new KVM PV features unless all
> > > supported kernels have it, we'd have to wait many years otherwise.
> > 
> > Yes, this is a known problem in fact. :(  In 6.0 we even support RHEL 7,
> > though that will go away in 6.1.
> > 
> > We should take the occasion of dropping RHEL7 to be clearer about which
> > kernels are supported.
> 
> It would be nice to be able to define sets of KVM functonality that we
> can either start given machine types with, or provide a separate switch
> to limit kvm functionality back to some defined point.  We do trip over
> the same things pretty regularly when accidentally turning on new
> features.

The same idea can apply to the hyperv=on stuff Vitaly is working
on.  Maybe we should consider making a generic version of the
s390x FeatGroup code, use it to define convenient sets of KVM and
hyperv features.

-- 
Eduardo