Date:   Tue, 8 Feb 2022 10:55:37 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 13/17] virtio_pci: queue_reset: support VIRTIO_F_RING_RESET

On Mon, Feb 7, 2022 at 4:19 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Mon, 7 Feb 2022 14:57:13 +0800, Jason Wang <jasowang@...hat.com> wrote:
> >
> > 在 2022/1/26 下午3:35, Xuan Zhuo 写道:
> > > This patch implements virtio pci support for QUEUE RESET.
> > >
> > > Performing reset on a queue is divided into two steps:
> > >
> > > 1. reset_vq: reset one vq
> > > 2. enable_reset_vq: re-enable the reset queue
> > >
> > > In the first step, these tasks will be completed:
> > >     1. notify the hardware queue to reset
> > >     2. recycle the buffer from vq
> > >     3. release the ring of the vq
> > >
> > > The process of enable reset vq:
> > >      vp_modern_enable_reset_vq()
> > >      vp_enable_reset_vq()
> > >      __vp_setup_vq()
> > >      setup_vq()
> > >      vring_setup_virtqueue()
> > >
> > > In this process, we added two parameters, vq and num, and finally passed
> > > them to vring_setup_virtqueue().  And reuse the original info and vq.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > ---
> > >   drivers/virtio/virtio_pci_common.c |  36 +++++++----
> > >   drivers/virtio/virtio_pci_common.h |   5 ++
> > >   drivers/virtio/virtio_pci_modern.c | 100 +++++++++++++++++++++++++++++
> > >   3 files changed, 128 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> > > index c02936d29a31..ad21638fbf66 100644
> > > --- a/drivers/virtio/virtio_pci_common.c
> > > +++ b/drivers/virtio/virtio_pci_common.c
> > > @@ -205,23 +205,28 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
> > >     return err;
> > >   }
> > >
> > > -static struct virtqueue *vp_setup_vq(struct virtio_device *vdev, unsigned index,
> > > -                                void (*callback)(struct virtqueue *vq),
> > > -                                const char *name,
> > > -                                bool ctx,
> > > -                                u16 msix_vec, u16 num)
> > > +struct virtqueue *vp_setup_vq(struct virtio_device *vdev, unsigned index,
> > > +                         void (*callback)(struct virtqueue *vq),
> > > +                         const char *name,
> > > +                         bool ctx,
> > > +                         u16 msix_vec, u16 num)
> > >   {
> > >     struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> > > -   struct virtio_pci_vq_info *info = kmalloc(sizeof *info, GFP_KERNEL);
> > > +   struct virtio_pci_vq_info *info;
> > >     struct virtqueue *vq;
> > >     unsigned long flags;
> > >
> > > -   /* fill out our structure that represents an active queue */
> > > -   if (!info)
> > > -           return ERR_PTR(-ENOMEM);
> > > +   info = vp_dev->vqs[index];
> > > +   if (!info) {
> > > +           info = kzalloc(sizeof *info, GFP_KERNEL);
> > > +
> > > +           /* fill out our structure that represents an active queue */
> > > +           if (!info)
> > > +                   return ERR_PTR(-ENOMEM);
> > > +   }
> > >
> > >     vq = vp_dev->setup_vq(vp_dev, info, index, callback, name, ctx,
> > > -                         msix_vec, NULL, num);
> > > +                         msix_vec, info->vq, num);
> > >     if (IS_ERR(vq))
> > >             goto out_info;
> > >
> > > @@ -238,6 +243,9 @@ static struct virtqueue *vp_setup_vq(struct virtio_device *vdev, unsigned index,
> > >     return vq;
> > >
> > >   out_info:
> > > +   if (info->vq && info->vq->reset)
> > > +           return vq;
> > > +
> > >     kfree(info);
> > >     return vq;
> > >   }
> > > @@ -248,9 +256,11 @@ 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_common.h b/drivers/virtio/virtio_pci_common.h
> > > index 65db92245e41..c1d15f7c0be4 100644
> > > --- a/drivers/virtio/virtio_pci_common.h
> > > +++ b/drivers/virtio/virtio_pci_common.h
> > > @@ -119,6 +119,11 @@ int vp_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> > >             struct virtqueue *vqs[], vq_callback_t *callbacks[],
> > >             const char * const names[], const bool *ctx,
> > >             struct irq_affinity *desc);
> > > +struct virtqueue *vp_setup_vq(struct virtio_device *vdev, unsigned index,
> > > +                         void (*callback)(struct virtqueue *vq),
> > > +                         const char *name,
> > > +                         bool ctx,
> > > +                         u16 msix_vec, u16 num);
> > >   const char *vp_bus_name(struct virtio_device *vdev);
> > >
> > >   /* Setup the affinity for a virtqueue:
> > > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > > index 2ce58de549de..6789411169e4 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 +179,94 @@ static void vp_reset(struct virtio_device *vdev)
> > >     vp_disable_cbs(vdev);
> > >   }
> > >
> > > +static int vp_modern_reset_vq(struct virtio_reset_vq *param)
> > > +{
> > > +   struct virtio_pci_device *vp_dev = to_vp_device(param->vdev);
> > > +   struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
> > > +   struct virtio_pci_vq_info *info;
> > > +   u16 msix_vec, queue_index;
> > > +   unsigned long flags;
> > > +   void *buf;
> > > +
> > > +   if (!virtio_has_feature(param->vdev, VIRTIO_F_RING_RESET))
> > > +           return -ENOENT;
> > > +
> > > +   queue_index = param->queue_index;
> > > +
> > > +   vp_modern_set_queue_reset(mdev, queue_index);
> > > +
> > > +   /* After write 1 to queue reset, the driver MUST wait for a read of
> > > +    * queue reset to return 1.
> > > +    */
> > > +   while (vp_modern_get_queue_reset(mdev, queue_index) != 1)
> > > +           msleep(1);
> >
> >
> > Is this better to move this logic into vp_modern_set_queue_reset()?
> >
>
> OK.
>
> >
> > > +
> > > +   info = vp_dev->vqs[queue_index];
> > > +   msix_vec = info->msix_vector;
> > > +
> > > +   /* Disable VQ callback. */
> > > +   if (vp_dev->per_vq_vectors && msix_vec != VIRTIO_MSI_NO_VECTOR)
> > > +           disable_irq(pci_irq_vector(vp_dev->pci_dev, msix_vec));
> >
> >
> > How about the INTX case where irq is shared? I guess we need to disable
> > and enable the irq as well.
>
> For the INTX scenario, I don't think we need to disable/enable the irq. But I do
> have a mistake, I should put the following list_del(&info->node) here, so that
> when the irq comes, it will no longer operate this vq.
>
> In fact, for no INTX case, the disable_irq here is not necessary, according to
> the requirements of the spec, after reset, the device should not generate irq
> anymore.

I may miss something but I don't think INTX differs from MSI from the
vq handler perspective.

> Here just to prevent accidents.

The problem is that if you don't disable/sync IRQ there could be a
race between the vq irq handler and the virtqueue_detach_unused_buf()?

>
> >
> >
> > > +
> > > +   while ((buf = virtqueue_detach_unused_buf(info->vq)) != NULL)
> > > +           param->free_unused_cb(param, buf);
> >
> >
> > Any reason that we can't leave this logic to driver? (Or is there any
> > operations that must be done before the following operations?)
>
> As you commented before, we merged free unused buf and reset queue.
>
> I think it's a good note, otherwise, we're going to
>
>         1. reset vq
>         2. free unused(by driver)
>         3. free ring of vq

Rethink about this, I'd prefer to leave it to the driver for consistency.

E.g the virtqueue_detach_unused_buf() is called by each driver nowdays.

>
>
> >
> >
> > > +
> > > +   /* delete vq */
> > > +   spin_lock_irqsave(&vp_dev->lock, flags);
> > > +   list_del(&info->node);
> > > +   spin_unlock_irqrestore(&vp_dev->lock, flags);
> > > +
> > > +   INIT_LIST_HEAD(&info->node);
> > > +
> > > +   if (vp_dev->msix_enabled)
> > > +           vp_modern_queue_vector(mdev, info->vq->index,
> > > +                                  VIRTIO_MSI_NO_VECTOR);
> >
> >
> > I wonder if this is a must.
> >
> >
> > > +
> > > +   if (!mdev->notify_base)
> > > +           pci_iounmap(mdev->pci_dev,
> > > +                       (void __force __iomem *)info->vq->priv);
> >
> >
> > Is this a must? what happens if we simply don't do this?
> >
>
> The purpose of these two operations is mainly to be symmetrical with del_vq().

This is another question I want to ask. Any reason for calling
del_vq()? Is it because you need to exclude a vq from the vq handler?

For any case, the MSI and notification stuff seems unnecessary.

Thanks

>
>
> >
> > > +
> > > +   vring_reset_virtqueue(info->vq);
> > > +
> > > +   return 0;
> > > +}
> > > +
> > > +static struct virtqueue *vp_modern_enable_reset_vq(struct virtio_reset_vq *param)
> > > +{
> > > +   struct virtio_pci_device *vp_dev = to_vp_device(param->vdev);
> > > +   struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
> > > +   struct virtio_pci_vq_info *info;
> > > +   u16 msix_vec, queue_index;
> > > +   struct virtqueue *vq;
> > > +
> > > +   if (!virtio_has_feature(param->vdev, VIRTIO_F_RING_RESET))
> > > +           return ERR_PTR(-ENOENT);
> > > +
> > > +   queue_index = param->queue_index;
> > > +
> > > +   info = vp_dev->vqs[queue_index];
> > > +
> > > +   if (!info->vq->reset)
> > > +           return ERR_PTR(-EPERM);
> > > +
> > > +   /* check queue reset status */
> > > +   if (vp_modern_get_queue_reset(mdev, queue_index) != 1)
> > > +           return ERR_PTR(-EBUSY);
> > > +
> > > +   vq = vp_setup_vq(param->vdev, queue_index, param->callback, param->name,
> > > +                    param->ctx, info->msix_vector, param->ring_num);
> > > +   if (IS_ERR(vq))
> > > +           return vq;
> > > +
> > > +   vp_modern_set_queue_enable(&vp_dev->mdev, vq->index, true);
> > > +
> > > +   msix_vec = vp_dev->vqs[queue_index]->msix_vector;
> > > +   if (vp_dev->per_vq_vectors && msix_vec != VIRTIO_MSI_NO_VECTOR)
> > > +           enable_irq(pci_irq_vector(vp_dev->pci_dev, msix_vec));
> >
> >
> > How about the INT-X case?
>
> Explained above.
>
> Thanks.
>
> >
> > Thanks
> >
> >
> > > +
> > > +   return vq;
> > > +}
> > > +
> > >   static u16 vp_config_vector(struct virtio_pci_device *vp_dev, u16 vector)
> > >   {
> > >     return vp_modern_config_vector(&vp_dev->mdev, vector);
> > > @@ -284,6 +375,11 @@ static void del_vq(struct virtio_pci_vq_info *info)
> > >     struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
> > >     struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
> > >
> > > +   if (vq->reset) {
> > > +           vring_del_virtqueue(vq);
> > > +           return;
> > > +   }
> > > +
> > >     if (vp_dev->msix_enabled)
> > >             vp_modern_queue_vector(mdev, vq->index,
> > >                                    VIRTIO_MSI_NO_VECTOR);
> > > @@ -403,6 +499,8 @@ 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 = {
> > > @@ -421,6 +519,8 @@ 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 */
> >
>

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