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

[Eugenio Perez Martin]

On Thu, Mar 14, 2024 at 9:24 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
>
>
>
> On 3/14/24 3:05 PM, Eugenio Perez Martin wrote:
> > 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.
> >
>
> Ahh okay I see what you mean. But I thought the following was checking
> for a valid VQ index:
>
> if (vq_idx < VIRTIO_QUEUE_MAX)
>

Right, but then the (potentially multiple) callers are responsible to
check for that. If we accept a VirtQueue *, it is assumed it is valid
already.

> Of course the virtio device may not have up to VIRTIO_QUEUE_MAX
> virtqueues, so maybe we should be checking for validity like this?
>
> if (vdev->vq[i].vring.num == 0)
>

Actually yes, if you're going to send a new version I think checking
against num is better. Good find!

> Or was there something else you had in mind? Apologies for the confusion.
>

No worries, virtio.c is full of checks like that :).

Thanks!

> > 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.
> >
>
> Roger, I'll use this instead for clarity.
>
> > 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! >
>
> I'll add it to the todo list =]
>
> >>>>>> +{
> >>>>>> +    /* 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
> >>>>>>
> >>>>>
> >>>>
> >>>
> >>
> >
>