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

[Eugenio Perez Martin]

On Thu, Mar 14, 2024 at 5:06 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
>
>
>
> 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?
>

No, that needs to be kept. I meant the access to vdev->vq[i] without
checking for a valid i.

You can get the VirtQueue in the caller with virtio_get_queue. Which
also does not check for a valid index, but that way is clearer the
caller needs to check it.

As a side note, the check for desc != 0 is widespread in QEMU but the
driver may use 0 address for desc, so it's not 100% valid. But to
change that now requires a deeper change out of the scope of this
series, so let's keep it for now :).

Thanks!

> >>>> +{
> >>>> +    /* 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
> >>>>
> >>>
> >>
> >
>