Re: [PATCH v7 17/26] virtio_pci: queue_reset: support VIRTIO_F_RING_RESET

Jason Wang
2022-03-11T05:09:53Z

在 2022/3/10 下午4:20, Xuan Zhuo 写道:
> On Wed, 9 Mar 2022 16:54:10 +0800, Jason Wang <jasowang@redhat.com> wrote:
>> 在 2022/3/8 下午8:35, Xuan Zhuo 写道:
>>> This patch implements virtio pci support for QUEUE RESET.
>>>
>>> Performing reset on a queue is divided into these steps:
>>>
>>> 1. virtio_reset_vq() - notify the device to reset the queue
>>> 2. virtqueue_detach_unused_buf() - recycle the buffer submitted
>>> 3. virtqueue_reset_vring() - reset the vring (may re-alloc)
>>> 4. virtio_enable_resetq() - mmap vring to device, and enable the queue
>>>
>>> This patch implements virtio_reset_vq(), virtio_enable_resetq() in the
>>> pci scenario.
>>>
>>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>>> ---
>>> drivers/virtio/virtio_pci_common.c | 8 +--
>>> drivers/virtio/virtio_pci_modern.c | 83 ++++++++++++++++++++++++++++++
>>> 2 files changed, 88 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
>>> index fdbde1db5ec5..863d3a8a0956 100644
>>> --- a/drivers/virtio/virtio_pci_common.c
>>> +++ b/drivers/virtio/virtio_pci_common.c
>>> @@ -248,9 +248,11 @@ static void vp_del_vq(struct virtqueue *vq)
>>> struct virtio_pci_vq_info *info = vp_dev->vqs[vq->index];
>>> unsigned long flags;
>>>
>>> - spin_lock_irqsave(&vp_dev->lock, flags);
>>> - list_del(&info->node);
>>> - spin_unlock_irqrestore(&vp_dev->lock, flags);
>>> + if (!vq->reset) {
>>> + spin_lock_irqsave(&vp_dev->lock, flags);
>>> + list_del(&info->node);
>>> + spin_unlock_irqrestore(&vp_dev->lock, flags);
>>> + }
>>>
>>> vp_dev->del_vq(info);
>>> kfree(info);
>>> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
>>> index 49a4493732cf..3c67d3607802 100644
>>> --- a/drivers/virtio/virtio_pci_modern.c
>>> +++ b/drivers/virtio/virtio_pci_modern.c
>>> @@ -34,6 +34,9 @@ static void vp_transport_features(struct virtio_device *vdev, u64 features)
>>> if ((features & BIT_ULL(VIRTIO_F_SR_IOV)) &&
>>> pci_find_ext_capability(pci_dev, PCI_EXT_CAP_ID_SRIOV))
>>> __virtio_set_bit(vdev, VIRTIO_F_SR_IOV);
>>> +
>>> + if (features & BIT_ULL(VIRTIO_F_RING_RESET))
>>> + __virtio_set_bit(vdev, VIRTIO_F_RING_RESET);
>>> }
>>>
>>> /* virtio config->finalize_features() implementation */
>>> @@ -199,6 +202,82 @@ static int vp_active_vq(struct virtqueue *vq, u16 msix_vec)
>>> return 0;
>>> }
>>>
>>> +static int vp_modern_reset_vq(struct virtqueue *vq)
>>> +{
>>> + struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
>>> + struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
>>> + struct virtio_pci_vq_info *info;
>>> + unsigned long flags;
>>> + unsigned int irq;
>>> +
>>> + if (!virtio_has_feature(vq->vdev, VIRTIO_F_RING_RESET))
>>> + return -ENOENT;
>>> +
>>> + vp_modern_set_queue_reset(mdev, vq->index);
>>> +
>>> + info = vp_dev->vqs[vq->index];
>>> +
>>> + /* delete vq from irq handler */
>>> + spin_lock_irqsave(&vp_dev->lock, flags);
>>> + list_del(&info->node);
>>> + spin_unlock_irqrestore(&vp_dev->lock, flags);
>>> +
>>> + INIT_LIST_HEAD(&info->node);
>>> +
>>> + vq->reset = VIRTIO_VQ_RESET_STEP_DEVICE;
>>> +
>>> + /* sync irq callback. */
>>> + if (vp_dev->intx_enabled) {
>>> + irq = vp_dev->pci_dev->irq;
>>> +
>>> + } else {
>>> + if (info->msix_vector == VIRTIO_MSI_NO_VECTOR)
>>> + return 0;
>>> +
>>> + irq = pci_irq_vector(vp_dev->pci_dev, info->msix_vector);
>>> + }
>>> +
>>> + synchronize_irq(irq);
>>
>> Synchronize_irq() is not sufficient here since it breaks the effort of
>> the interrupt hardening which is done by commits:
>>
>> 080cd7c3ac87 virtio-pci: harden INTX interrupts
>> 9e35276a5344 virtio_pci: harden MSI-X interrupts
>>
>> Unfortunately  080cd7c3ac87 introduces an issue that disable_irq() were
>> used for the affinity managed irq but we're discussing a fix.
>>
>
> ok, I think disable_irq() is still used here.
>
> I want to determine the solution for this detail first. So I posted the code, I
> hope Jason can help confirm this point first.
>
> There are three situations in which vq corresponds to an interrupt
>
> 1. intx
> 2. msix: per vq vectors
> 2. msix: share irq
>
> Essentially can be divided into two categories: per vq vectors and share irq.
>
> For share irq is based on virtqueues to find vq, so I think it is safe as long
> as list_del() is executed under the protection of the lock.
>
> In the case of per vq vectors, disable_irq() is used.

See the discussion here[1], disable_irq() could be problematic for the
block and scsi device that using affinity managed irq. We're waiting for
the IRQ maintainer to comment on a solution. Other looks sane.

Thanks

[1] https://lkml.org/lkml/2022/3/8/743

>
> Thanks.
>
> +static int vp_modern_reset_vq(struct virtqueue *vq)
> +{
> + struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
> + struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
> + struct virtio_pci_vq_info *info;
> + unsigned long flags;
> + unsigned int irq;
> +
> + if (!virtio_has_feature(vq->vdev, VIRTIO_F_RING_RESET))
> + return -ENOENT;
> +
> + vp_modern_set_queue_reset(mdev, vq->index);
> +
> + info = vp_dev->vqs[vq->index];
> +
> + /* delete vq from irq handler */
> + spin_lock_irqsave(&vp_dev->lock, flags);
> + list_del(&info->node);
> + vp_modern_set_queue_reset(mdev, vq->index);
> +
> + info = vp_dev->vqs[vq->index];
> +
> + /* delete vq from irq handler */
> + spin_lock_irqsave(&vp_dev->lock, flags);
> + list_del(&info->node);
> + spin_unlock_irqrestore(&vp_dev->lock, flags);
> +
> + INIT_LIST_HEAD(&info->node);
> +
> + /* For the case where vq has an exclusive irq, to prevent the irq from
> + * being received again and the pending irq, call disable_irq().
> + *
> + * In the scenario based on shared interrupts, vq will be searched from
> + * the queue virtqueues. Since the previous list_del() has been deleted
> + * from the queue, it is impossible for vq to be called in this case.
> + * There is no need to close the corresponding interrupt.
> + */
> + if (vp_dev->per_vq_vectors && msix_vec != VIRTIO_MSI_NO_VECTOR)
> + disable_irq(pci_irq_vector(vp_dev->pci_dev, info->msix_vector));
> +
> + vq->reset = true;
> +
> + return 0;
> +}
> +
> +static int vp_modern_enable_reset_vq(struct virtqueue *vq)
> +{
> + struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
> + struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
> + struct virtio_pci_vq_info *info;
> + unsigned long flags, index;
> + int err;
> +
> + if (!vq->reset)
> + return -EBUSY;
> +
> + index = vq->index;
> + info = vp_dev->vqs[index];
> +
> + /* check queue reset status */
> + if (vp_modern_get_queue_reset(mdev, index) != 1)
> + return -EBUSY;
> +
> + err = vp_active_vq(vq, info->msix_vector);
> + if (err)
> + return err;
> +
> + if (vq->callback) {
> + spin_lock_irqsave(&vp_dev->lock, flags);
> + list_add(&info->node, &vp_dev->virtqueues);
> + spin_unlock_irqrestore(&vp_dev->lock, flags);
> + } else {
> + INIT_LIST_HEAD(&info->node);
> + }
> +
> + vp_modern_set_queue_enable(&vp_dev->mdev, index, true);
> + vq->reset = false;
> +
> + if (vp_dev->per_vq_vectors && msix_vec != VIRTIO_MSI_NO_VECTOR)
> + enable_irq(pci_irq_vector(vp_dev->pci_dev, info->msix_vector));
> +
> + return 0;
> +}
>
>