Re: [PATCH v1 2/8] virtio-pci: Lock ioeventfd state with VIRTIO_F_NOTIFICATION_DATA

[Jonah Palmer]

On 3/8/24 12:36 PM, Eugenio Perez Martin wrote:
> On Fri, Mar 8, 2024 at 6: 01 PM Michael S. Tsirkin <mst@ redhat. com> 
> wrote: > > On Mon, Mar 04, 2024 at 02: 46: 06PM -0500, Jonah Palmer 
> wrote: > > Prevent ioeventfd from being enabled/disabled when a 
> virtio-pci > > device
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> On Fri, Mar 8, 2024 at 6:01 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Mon, Mar 04, 2024 at 02:46:06PM -0500, Jonah Palmer wrote:
> > > Prevent ioeventfd from being enabled/disabled when a virtio-pci
> > > device has negotiated the VIRTIO_F_NOTIFICATION_DATA transport
> > > feature.
> > >
> > > Due to ioeventfd not being able to carry the extra data associated with
> > > this feature, the ioeventfd should be left in a disabled state for
> > > emulated virtio-pci devices using this feature.
> > >
> > > Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
> > > Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> >
> > I thought hard about this. I propose that for now,
> > instead of disabling ioevetfd silently we error out unless
> > user disabled it for us.
> > WDYT?
>
> Yes, error is a better plan than silently disabling it. In the
> (unlikely?) case we are able to make notification data work with
> eventfd in the future, it makes the change more evident.

Will do in v2. I assume we'll also make this the case for virtio-mmio 
and virtio-ccw?

> > > ---
> > >  hw/virtio/virtio-pci.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > > index d12edc567f..287b8f7720 100644
> > > --- a/hw/virtio/virtio-pci.c
> > > +++ b/hw/virtio/virtio-pci.c
> > > @@ -417,13 +417,15 @@ static void virtio_ioport_write(void *opaque, uint32_t 
> > addr, uint32_t val)
> > >          }
> > >          break;
> > >      case VIRTIO_PCI_STATUS:
> > > -        if (!(val & VIRTIO_CONFIG_S_DRIVER_OK)) {
> > > +        if (!(val & VIRTIO_CONFIG_S_DRIVER_OK) &&
> > > +            !virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA)) {
> > >              virtio_pci_stop_ioeventfd(proxy);
> > >          }
> > >
> > >          virtio_set_status(vdev, val & 0xFF);
> > >
> > > -        if (val & VIRTIO_CONFIG_S_DRIVER_OK) {
> > > +        if ((val & VIRTIO_CONFIG_S_DRIVER_OK) &&
> > > +            !virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA)) {
> > >              virtio_pci_start_ioeventfd(proxy);
> > >          }
> > >
> > > --
> > > 2.39.3