Re: [Qemu-devel] [Qemu-ppc] [PATCH] virtio-pci: fix host notifiers on bi-endian architectures

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Mar 11, 2015 at 11:52:13PM +0100, Greg Kurz wrote:
> On Thu, 12 Mar 2015 09:18:38 +1100
> Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
> 
> > On Wed, 2015-03-11 at 23:03 +0100, Greg Kurz wrote:
> > 
> > > /* The host notifier will be swapped in adjust_endianness() according to the
> > >  * target default endianness. We need to negate this swap if the device uses
> > >  * an endianness that is not the default (ppc64le for example).
> > >  */
> > > 
> > > > > +static uint16_t cpu_to_host_notifier16(VirtIODevice *vdev, uint16_t val)
> > > > > +{
> > > > > +    return virtio_is_big_endian(vdev) ? val : bswap16(val);
> > > > > +}
> > 
> > But but but ... The above ... won't it do things like break x86 ? Ie,
> > shouldn't we swap only if TARGET_BIG_ENDIAN and !virtio_is_big_endian ?
> > Or better, "fixed target endian" ^ "virtio endian" to cover all cases ?
> > 
> 
> Yeah you're right, it's a mess :)
> 
> To avoid virtio-pci.o being built per target, we can use virtio_default_endian()
> instead (to be exported from virtio.c):
> 
> return vdev->device_endian() != virtio_default_endian() ? val : bswap16(val);
> 
> I shall test on x86 and post a v2.
> 
> Thanks.
> 
> --
> G

It's a mess because the issue is not in virtio I think.
virtio common region is just a simple device, using
fixed LE format.
It's some bug in ioeventfd support. Need to understand
whether it's in kernel (and maybe do a work-around)
or in qemu memory core.


> > Cheers,
> > Ben.
> > 
> > > > >  static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
> > > > >                                                   int n, bool assign, bool set_handler)
> > > > >  {
> > > > > @@ -150,10 +155,12 @@ static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
> > > > >          }
> > > > >          virtio_queue_set_host_notifier_fd_handler(vq, true, set_handler);
> > > > >          memory_region_add_eventfd(&proxy->bar, VIRTIO_PCI_QUEUE_NOTIFY, 2,
> > > > > -                                  true, n, notifier);
> > > > > +                                  true, cpu_to_host_notifier16(vdev, n),
> > > > > +                                  notifier);
> > > > >      } else {
> > > > >          memory_region_del_eventfd(&proxy->bar, VIRTIO_PCI_QUEUE_NOTIFY, 2,
> > > > > -                                  true, n, notifier);
> > > > > +                                  true, cpu_to_host_notifier16(vdev, n),
> > > > > +                                  notifier);
> > > > >          virtio_queue_set_host_notifier_fd_handler(vq, false, false);
> > > > >          event_notifier_cleanup(notifier);
> > > > >      }
> > > > 
> > > 
> > 
> >