Re: [PATCH 0/5] vfio/spapr: Handle changes of master irq chip for VFIO devices

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 22 Nov 2019 12:18:24 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Thu, Nov 21, 2019 at 09:57:38AM -0700, Alex Williamson wrote:
> > On Thu, 21 Nov 2019 11:56:02 +1100
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > Due to the way feature negotiation works in PAPR (which is a
> > > paravirtualized platform), we can end up changing the global irq chip
> > > at runtime, including it's KVM accelerate model.  That causes
> > > complications for VFIO devices with INTx, which wire themselves up
> > > directly to the KVM irqchip for performance.
> > > 
> > > This series introduces a new notifier to let VFIO devices (and
> > > anything else that needs to in the future) know about changes to the
> > > master irqchip.  It modifies VFIO to respond to the notifier,
> > > reconnecting itself to the new KVM irqchip as necessary.
> > > 
> > > In particular this removes a misleading (though not wholly inaccurate)
> > > warning that occurs when using VFIO devices on a pseries machine type
> > > guest.
> > > 
> > > Open question: should this go into qemu-4.2 or wait until 5.0?  It's
> > > has medium complexity / intrusiveness, but it *is* a bugfix that I
> > > can't see a simpler way to fix.  It's effectively a regression from
> > > qemu-4.0 to qemu-4.1 (because that introduced XIVE support by
> > > default), although not from 4.1 to 4.2.  
> > 
> > Looks reasonable to me for 4.2, the vfio changes are not as big as they
> > appear.  If Paolo approves this week, I can send a pull request,
> > otherwise I can leave my ack for someone else as I'll be on PTO/holiday
> > next week.  Thanks,  
> 
> I'm happy to take it through my tree, and expect to be sending a PR in
> that timescale, so an ack sounds good.
> 
> I've pulled the series into my ppc-for-4.2 branch tentatively.
> 

Tested-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>