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Commit 98f9ca0a authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
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vhost: replace rcu with mutex 



All memory accesses are done under some VQ mutex.
So lock/unlock all VQs is a faster equivalent of synchronize_rcu()
for memory access changes.
Some guests cause a lot of these changes, so it's helpful
to make them faster.

Reported-by: default avatar"Gonglei (Arei)" <arei.gonglei@huawei.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 23cc5a99

drivers/vhost/vhost.c

+9 −1
Original line number Diff line number Diff line
@@ -593,6 +593,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) 
{

	struct vhost_memory mem, *newmem, *oldmem;

	unsigned long size = offsetof(struct vhost_memory, regions);

	int i;



	if (copy_from_user(&mem, m, size))

		return -EFAULT;
@@ -619,7 +620,14 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) 
	oldmem = rcu_dereference_protected(d->memory,

					   lockdep_is_held(&d->mutex));

	rcu_assign_pointer(d->memory, newmem);

	synchronize_rcu();



	/* All memory accesses are done under some VQ mutex.

	 * So below is a faster equivalent of synchronize_rcu()

	 */

	for (i = 0; i < d->nvqs; ++i) {

		mutex_lock(&d->vqs[i]->mutex);

		mutex_unlock(&d->vqs[i]->mutex);

	}

	kfree(oldmem);

	return 0;

}