[PATCH v2 3/4] virtio: Protect vqs list access

[Parav Pandit via Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

VQs may be accessed to mark the device broken while they are
created/destroyed. Hence protect the access to the vqs list.

Fixes: e2dcdfe95c0b ("virtio: virtio_break_device() to mark all virtqueues broken.")
Signed-off-by: Parav Pandit <parav@xxxxxxxxxx>
---
changelog:
v1->v2:
 - use the hole in current struct to place vqs_list_lock to have natural packing
v0->v1:
 - use spinlock instead of rwlock
---
 drivers/virtio/virtio.c      | 1 +
 drivers/virtio/virtio_ring.c | 8 ++++++++
 include/linux/virtio.h       | 1 +
 3 files changed, 10 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 4b15c00c0a0a..49984d2cba24 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -355,6 +355,7 @@ int register_virtio_device(struct virtio_device *dev)
 	virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
 
 	INIT_LIST_HEAD(&dev->vqs);
+	spin_lock_init(&dev->vqs_list_lock);
 
 	/*
 	 * device_add() causes the bus infrastructure to look for a matching
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index d5934c2e5a89..c2aaa0eff6df 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1755,7 +1755,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
 			cpu_to_le16(vq->packed.event_flags_shadow);
 	}
 
+	spin_lock(&vdev->vqs_list_lock);
 	list_add_tail(&vq->vq.list, &vdev->vqs);
+	spin_unlock(&vdev->vqs_list_lock);
 	return &vq->vq;
 
 err_desc_extra:
@@ -2229,7 +2231,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	memset(vq->split.desc_state, 0, vring.num *
 			sizeof(struct vring_desc_state_split));
 
+	spin_lock(&vdev->vqs_list_lock);
 	list_add_tail(&vq->vq.list, &vdev->vqs);
+	spin_unlock(&vdev->vqs_list_lock);
 	return &vq->vq;
 
 err_extra:
@@ -2291,7 +2295,9 @@ void vring_del_virtqueue(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
+	spin_lock(&vq->vq.vdev->vqs_list_lock);
 	list_del(&_vq->list);
+	spin_unlock(&vq->vq.vdev->vqs_list_lock);
 
 	if (vq->we_own_ring) {
 		if (vq->packed_ring) {
@@ -2386,12 +2392,14 @@ void virtio_break_device(struct virtio_device *dev)
 {
 	struct virtqueue *_vq;
 
+	spin_lock(&dev->vqs_list_lock);
 	list_for_each_entry(_vq, &dev->vqs, list) {
 		struct vring_virtqueue *vq = to_vvq(_vq);
 
 		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
 		WRITE_ONCE(vq->broken, true);
 	}
+	spin_unlock(&dev->vqs_list_lock);
 }
 EXPORT_SYMBOL_GPL(virtio_break_device);
 
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index b1894e0323fa..41edbc01ffa4 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -110,6 +110,7 @@ struct virtio_device {
 	bool config_enabled;
 	bool config_change_pending;
 	spinlock_t config_lock;
+	spinlock_t vqs_list_lock; /* Protects VQs list access */
 	struct device dev;
 	struct virtio_device_id id;
 	const struct virtio_config_ops *config;
-- 
2.27.0

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