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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Thu, 12 Mar 2015 09:18:38 +1100
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Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH] virtio-pci: fix host notifiers
 on bi-endian architectures
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To: Greg Kurz <gkurz@linux.vnet.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>, qemu-ppc@nongnu.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, "Michael S. Tsirkin" <mst@redhat.com>

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 ?

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);
> > >      }
> > 
>