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SubjectRe: [PATCH v6 6/8] virtio_vdpa: setup correct vq size with callbacks get_vq_num_{max,min}
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在 2021/10/25 上午10:44, Wu Zongyong 写道:
> On Mon, Oct 25, 2021 at 10:22:30AM +0800, Jason Wang wrote:
>> On Fri, Oct 22, 2021 at 10:45 AM Wu Zongyong
>> <wuzongyong@linux.alibaba.com> wrote:
>>> For the devices which implement the get_vq_num_min callback, the driver
>>> should not negotiate with virtqueue size with the backend vdpa device if
>>> the value returned by get_vq_num_min equals to the value returned by
>>> get_vq_num_max.
>>> This is useful for vdpa devices based on legacy virtio specfication.
>>>
>>> Signed-off-by: Wu Zongyong <wuzongyong@linux.alibaba.com>
>>> ---
>>> drivers/virtio/virtio_vdpa.c | 21 ++++++++++++++++-----
>>> 1 file changed, 16 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
>>> index 72eaef2caeb1..e42ace29daa1 100644
>>> --- a/drivers/virtio/virtio_vdpa.c
>>> +++ b/drivers/virtio/virtio_vdpa.c
>>> @@ -145,7 +145,8 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
>>> /* Assume split virtqueue, switch to packed if necessary */
>>> struct vdpa_vq_state state = {0};
>>> unsigned long flags;
>>> - u32 align, num;
>>> + u32 align, max_num, min_num = 0;
>>> + bool may_reduce_num = true;
>>> int err;
>>>
>>> if (!name)
>>> @@ -163,22 +164,32 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
>>> if (!info)
>>> return ERR_PTR(-ENOMEM);
>>>
>>> - num = ops->get_vq_num_max(vdpa);
>>> - if (num == 0) {
>>> + max_num = ops->get_vq_num_max(vdpa);
>>> + if (max_num == 0) {
>>> err = -ENOENT;
>>> goto error_new_virtqueue;
>>> }
>>>
>>> + if (ops->get_vq_num_min)
>>> + min_num = ops->get_vq_num_min(vdpa);
>>> +
>>> + may_reduce_num = (max_num == min_num) ? false : true;
>>> +
>>> /* Create the vring */
>>> align = ops->get_vq_align(vdpa);
>>> - vq = vring_create_virtqueue(index, num, align, vdev,
>>> - true, true, ctx,
>>> + vq = vring_create_virtqueue(index, max_num, align, vdev,
>>> + true, may_reduce_num, ctx,
>>> virtio_vdpa_notify, callback, name);
>>> if (!vq) {
>>> err = -ENOMEM;
>>> goto error_new_virtqueue;
>>> }
>>>
>>> + if (virtqueue_get_vring_size(vq) < min_num) {
>>> + err = -EINVAL;
>>> + goto err_vq;
>>> + }
>> I wonder under which case can we hit this?
>>
>> Thanks
> If min_vq_num < max_vq_num, may_reduce_num should be true, then it is
> possible to allocate a virtqueue with a small size which value is less
> than the min_vq_num since we only set the upper bound for virtqueue size
> when creating virtqueue.
>
> Refers to vring_create_virtqueue_split in driver/virtio/virtio_vring.c:
>
> for (; num && vring_size(num, vring_align) > PAGE_SIZE; num /= 2) {
> queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
> &dma_addr,
> GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
> if (queue)
> break;
> if (!may_reduce_num)
> return NULL;
> }


It looks to me it's better to fix this function instead of checking it
in the caller?


>
> BTW, I have replied this mail on Nov.18, have you ever received it?


For some reason I dont' get that.

Thanks


>>> +
>>> /* Setup virtqueue callback */
>>> cb.callback = virtio_vdpa_virtqueue_cb;
>>> cb.private = info;
>>> --
>>> 2.31.1
>>>

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