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

On Wed, 9 Mar 2022 16:54:10 +0800, Jason Wang [off-list ref] wrote:

在 2022/3/8 下午8:35, Xuan Zhuo 写道:

quoted

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.

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;
+}


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