Re: [PATCH v2 1/6] virtio/virtio-pci: Handle extra notification data

[Jonah Palmer]

On 3/14/24 10:55 AM, Eugenio Perez Martin wrote:
> On Thu, Mar 14, 2024 at 1:16 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
> > On 3/13/24 11:01 PM, Jason Wang wrote:
> > > On Wed, Mar 13, 2024 at 7:55 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
> > > > Add support to virtio-pci devices for handling the extra data sent
> > > > from the driver to the device when the VIRTIO_F_NOTIFICATION_DATA
> > > > transport feature has been negotiated.
> > > >
> > > > The extra data that's passed to the virtio-pci device when this
> > > > feature is enabled varies depending on the device's virtqueue
> > > > layout.
> > > >
> > > > In a split virtqueue layout, this data includes:
> > > >    - upper 16 bits: shadow_avail_idx
> > > >    - lower 16 bits: virtqueue index
> > > >
> > > > In a packed virtqueue layout, this data includes:
> > > >    - upper 16 bits: 1-bit wrap counter & 15-bit shadow_avail_idx
> > > >    - lower 16 bits: virtqueue index
> > > >
> > > > Tested-by: Lei Yang <leiyang@redhat.com>
> > > > Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
> > > > Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> > > > ---
> > > >    hw/virtio/virtio-pci.c     | 10 +++++++---
> > > >    hw/virtio/virtio.c         | 18 ++++++++++++++++++
> > > >    include/hw/virtio/virtio.h |  1 +
> > > >    3 files changed, 26 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > > > index cb6940fc0e..0f5c3c3b2f 100644
> > > > --- a/hw/virtio/virtio-pci.c
> > > > +++ b/hw/virtio/virtio-pci.c
> > > > @@ -384,7 +384,7 @@ static void virtio_ioport_write(void *opaque, uint32_t 
> > > > addr, uint32_t val)
> > > >    {
> > > >        VirtIOPCIProxy *proxy = opaque;
> > > >        VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
> > > > -    uint16_t vector;
> > > > +    uint16_t vector, vq_idx;
> > > >        hwaddr pa;
> > > >
> > > >        switch (addr) {
> > > > @@ -408,8 +408,12 @@ static void virtio_ioport_write(void *opaque, uint32_t 
> > > > addr, uint32_t val)
> > > >                vdev->queue_sel = val;
> > > >            break;
> > > >        case VIRTIO_PCI_QUEUE_NOTIFY:
> > > > -        if (val < VIRTIO_QUEUE_MAX) {
> > > > -            virtio_queue_notify(vdev, val);
> > > > +        vq_idx = val;
> > > > +        if (vq_idx < VIRTIO_QUEUE_MAX) {
> > > > +            if (virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA)) {
> > > > +                virtio_queue_set_shadow_avail_data(vdev, val);
> > > > +            }
> > > > +            virtio_queue_notify(vdev, vq_idx);
> > > >            }
> > > >            break;
> > > >        case VIRTIO_PCI_STATUS:
> > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > > > index d229755eae..bcb9e09df0 100644
> > > > --- a/hw/virtio/virtio.c
> > > > +++ b/hw/virtio/virtio.c
> > > > @@ -2255,6 +2255,24 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, 
> > > > int align)
> > > >        }
> > > >    }
> > > >
> > > > +void virtio_queue_set_shadow_avail_data(VirtIODevice *vdev, uint32_t data)
>
> Maybe I didn't explain well, but I think it is better to pass directly
> idx to a VirtQueue *. That way only the caller needs to check for a
> valid vq idx, and (my understanding is) the virtio.c interface is
> migrating to VirtQueue * use anyway.

Oh, are you saying to just pass in a VirtQueue *vq instead of 
VirtIODevice *vdev and get rid of the vq->vring.desc check in the function?

> > > > +{
> > > > +    /* Lower 16 bits is the virtqueue index */
> > > > +    uint16_t i = data;
> > > > +    VirtQueue *vq = &vdev->vq[i];
> > > > +
> > > > +    if (!vq->vring.desc) {
> > > > +        return;
> > > > +    }
> > > > +
> > > > +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> > > > +        vq->shadow_avail_wrap_counter = (data >> 31) & 0x1;
> > > > +        vq->shadow_avail_idx = (data >> 16) & 0x7FFF;
> > > > +    } else {
> > > > +        vq->shadow_avail_idx = (data >> 16);
> > >
> > > Do we need to do a sanity check for this value?
> > >
> > > Thanks
> >
> > It can't hurt, right? What kind of check did you have in mind?
> >
> > if (vq->shadow_avail_idx >= vq->vring.num)
>
> I'm a little bit lost too. shadow_avail_idx can take all uint16_t
> values. Maybe you meant checking for a valid vq index, Jason?
>
> Thanks!
>
> > Or something else?
> >
> > > > +    }
> > > > +}
> > > > +
> > > >    static void virtio_queue_notify_vq(VirtQueue *vq)
> > > >    {
> > > >        if (vq->vring.desc && vq->handle_output) {
> > > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > > > index c8f72850bc..53915947a7 100644
> > > > --- a/include/hw/virtio/virtio.h
> > > > +++ b/include/hw/virtio/virtio.h
> > > > @@ -335,6 +335,7 @@ void virtio_queue_update_rings(VirtIODevice *vdev, int n);
> > > >    void virtio_init_region_cache(VirtIODevice *vdev, int n);
> > > >    void virtio_queue_set_align(VirtIODevice *vdev, int n, int align);
> > > >    void virtio_queue_notify(VirtIODevice *vdev, int n);
> > > > +void virtio_queue_set_shadow_avail_data(VirtIODevice *vdev, uint32_t data);
> > > >    uint16_t virtio_queue_vector(VirtIODevice *vdev, int n);
> > > >    void virtio_queue_set_vector(VirtIODevice *vdev, int n, uint16_t vector);
> > > >    int virtio_queue_set_host_notifier_mr(VirtIODevice *vdev, int n,
> > > > --
> > > > 2.39.3