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Commit 788e5b3a authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

virtio_ring: use virt_store_mb 



We need a full barrier after writing out event index, using
virt_store_mb there seems better than open-coding.  As usual, we need a
wrapper to account for strong barriers.

It's tempting to use this in vhost as well, for that, we'll
need a variant of smp_store_mb that works on __user pointers.

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
parent 9e3f84ce

drivers/virtio/virtio_ring.c

+9 −6
Original line number Diff line number Diff line
@@ -517,10 +517,10 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len) 
	/* If we expect an interrupt for the next entry, tell host

	 * by writing event index and flush out the write before

	 * the read in the next get_buf call. */

	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {

		vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx);

		virtio_mb(vq->weak_barriers);

	}

	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))

		virtio_store_mb(vq->weak_barriers,

				&vring_used_event(&vq->vring),

				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));



#ifdef DEBUG

	vq->last_add_time_valid = false;
@@ -653,8 +653,11 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) 
	}

	/* TODO: tune this threshold */

	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;

	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs);

	virtio_mb(vq->weak_barriers);



	virtio_store_mb(vq->weak_barriers,

			&vring_used_event(&vq->vring),

			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));



	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) - vq->last_used_idx) > bufs)) {

		END_USE(vq);

		return false;

include/linux/virtio_ring.h

+11 −0
Original line number Diff line number Diff line
@@ -45,6 +45,17 @@ static inline void virtio_wmb(bool weak_barriers) 
		wmb();

}



static inline void virtio_store_mb(bool weak_barriers,

				   __virtio16 *p, __virtio16 v)

{

	if (weak_barriers) {

		virt_store_mb(*p, v);

	} else {

		WRITE_ONCE(*p, v);

		mb();

	}

}



struct virtio_device;

struct virtqueue;