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

On 3/14/24 3:05 PM, Eugenio Perez Martin wrote:
> On Thu, Mar 14, 2024 at 5:06 PM Jonah Palmer <[email protected]> wrote:
>>
>>
>>
>> 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?
>>
> 
> 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)

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)

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

> 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
>>>>>>
>>>>>
>>>>
>>>
>>
>