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

On 3/14/24 10:55 AM, Eugenio Perez Martin wrote:
> On Thu, Mar 14, 2024 at 1:16 PM Jonah Palmer <[email protected]> wrote:
>>
>>
>>
>> On 3/13/24 11:01 PM, Jason Wang wrote:
>>> On Wed, Mar 13, 2024 at 7:55 PM Jonah Palmer <[email protected]> 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 <[email protected]>
>>>> Reviewed-by: Eugenio Pérez <[email protected]>
>>>> Signed-off-by: Jonah Palmer <[email protected]>
>>>> ---
>>>>    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
>>>>
>>>
>>
>