Re: [PATCH v5 14/22] virtio_pci: queue_reset: support VIRTIO_F_RING_RESET

[Jason Wang <jasowang@redhat.com>]

On Wed, Feb 16, 2022 at 4:08 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Wed, 16 Feb 2022 12:14:25 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > On Mon, Feb 14, 2022 at 4:14 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > This patch implements virtio pci support for QUEUE RESET.
> > >
> > > Performing reset on a queue is divided into these steps:
> > >
> > > 1. reset_vq: reset one vq
> > > 2. recycle the buffer from vq by virtqueue_detach_unused_buf()
> > > 3. release the ring of the vq by vring_release_virtqueue()
> > > 4. enable_reset_vq: re-enable the reset queue
> > >
> > > This patch implements reset_vq, enable_reset_vq 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 | 60 ++++++++++++++++++++++++++++++
> > >  2 files changed, 65 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> > > index 5a4f750a0b97..9ea319b1d404 100644
> > > --- a/drivers/virtio/virtio_pci_common.c
> > > +++ b/drivers/virtio/virtio_pci_common.c
> > > @@ -255,9 +255,11 @@ 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 bed3e9b84272..7d28f4c36fc2 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 */
> > > @@ -176,6 +179,59 @@ static void vp_reset(struct virtio_device *vdev)
> > >         vp_disable_cbs(vdev);
> > >  }
> > >
> > > +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;
> > > +
> > > +       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];
> > > +
> >
> > Any reason that we don't need to disable irq here as the previous versions did?
>
> Based on the spec, for the case of one interrupt per queue, there will be no
> more interrupts after the reset queue operation. Whether the interrupt is turned
> off or not has no effect. I turned off the interrupt before just to be safe.

So:

1) CPU0 -> get an interrupt
2) CPU1 -> vp_modern_reset_vq
2) CPU0 -> do_IRQ()

We still need to synchronize with the irq handler in this case?

Thanks

>
> And for irq sharing scenarios, I don't want to turn off shared interrupts for a
> queue.
>
> And the following list_del has been guaranteed to be safe, so I removed the code
> for closing interrupts in the previous version.
>
> Thanks.
>
> >
> >
> > > +       /* 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 = VIRTQUEUE_RESET_STAGE_DEVICE;
> > > +
> > > +       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;
> > > +       struct virtqueue *_vq;
> > > +
> > > +       if (vq->reset != VIRTQUEUE_RESET_STAGE_RELEASE)
> > > +               return -EBUSY;
> > > +
> > > +       /* check queue reset status */
> > > +       if (vp_modern_get_queue_reset(mdev, vq->index) != 1)
> > > +               return -EBUSY;
> > > +
> > > +       info = vp_dev->vqs[vq->index];
> > > +       _vq = vp_setup_vq(vq->vdev, vq->index, NULL, NULL, NULL,
> > > +                        info->msix_vector);
> >
> > So we only care about moden devices, this means using vp_setup_vq()
> > with NULL seems tricky.
> >
> > As replied in another thread, I would simply ask the caller to call
> > the vring reallocation helper. See the reply for patch 17.

Right.

Thanks.

> >
> > Thanks
> >
> >
> > > +       if (IS_ERR(_vq)) {
> > > +               vq->reset = VIRTQUEUE_RESET_STAGE_RELEASE;
> > > +               return PTR_ERR(_vq);
> > > +       }
> > > +
> > > +       vp_modern_set_queue_enable(&vp_dev->mdev, vq->index, true);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > >  static u16 vp_config_vector(struct virtio_pci_device *vp_dev, u16 vector)
> > >  {
> > >         return vp_modern_config_vector(&vp_dev->mdev, vector);
> > > @@ -397,6 +453,8 @@ static const struct virtio_config_ops virtio_pci_config_nodev_ops = {
> > >         .set_vq_affinity = vp_set_vq_affinity,
> > >         .get_vq_affinity = vp_get_vq_affinity,
> > >         .get_shm_region  = vp_get_shm_region,
> > > +       .reset_vq        = vp_modern_reset_vq,
> > > +       .enable_reset_vq = vp_modern_enable_reset_vq,
> > >  };
> > >
> > >  static const struct virtio_config_ops virtio_pci_config_ops = {
> > > @@ -415,6 +473,8 @@ static const struct virtio_config_ops virtio_pci_config_ops = {
> > >         .set_vq_affinity = vp_set_vq_affinity,
> > >         .get_vq_affinity = vp_get_vq_affinity,
> > >         .get_shm_region  = vp_get_shm_region,
> > > +       .reset_vq        = vp_modern_reset_vq,
> > > +       .enable_reset_vq = vp_modern_enable_reset_vq,
> > >  };
> > >
> > >  /* the PCI probing function */
> > > --
> > > 2.31.0
> > >
> >
>