On Thu, Jan 25, 2018 at 04:06:53PM +0100, Maxime Coquelin wrote:
> In the unlikely case the IOTLB memory pool runs out of memory,
> an issue may happen if all entries are used by the IOTLB cache,
> and an IOTLB miss happen. If the iotlb pending list is empty,
> then no memory is freed and allocation fails a second time.
>
> This patch fixes this by doing an IOTLB cache random evict if
> the IOTLB pending list is empty, ensuring the second allocation
> try will succeed.
>
> In the same spirit, the opposite is done when inserting an
> IOTLB entry in the IOTLB cache fails due to out of memory. In
> this case, the IOTLB pending is flushed if the IOTLB cache is
> empty to ensure the new entry can be inserted.
>
> Fixes: d012d1f293f4 ("vhost: add IOTLB helper functions")
> Fixes: f72c2ad63aeb ("vhost: add pending IOTLB miss request list and helpers")
>
[...]
> @@ -95,9 +98,11 @@ vhost_user_iotlb_pending_insert(struct vhost_virtqueue *vq,
>
> ret = rte_mempool_get(vq->iotlb_pool, (void **)&node);
> if (ret) {
> - RTE_LOG(INFO, VHOST_CONFIG,
> - "IOTLB pool empty, clear pending misses\n");
> - vhost_user_iotlb_pending_remove_all(vq);
> + RTE_LOG(INFO, VHOST_CONFIG, "IOTLB pool empty, clear
> entries\n");
> + if (!TAILQ_EMPTY(&vq->iotlb_pending_list))
> + vhost_user_iotlb_pending_remove_all(vq);
> + else
> + vhost_user_iotlb_cache_random_evict(vq);
> ret = rte_mempool_get(vq->iotlb_pool, (void **)&node);
> if (ret) {
> RTE_LOG(ERR, VHOST_CONFIG, "IOTLB pool still empty,
> failure\n");
> @@ -186,8 +191,11 @@ vhost_user_iotlb_cache_insert(struct vhost_virtqueue
> *vq, uint64_t iova,
>
> ret = rte_mempool_get(vq->iotlb_pool, (void **)&new_node);
> if (ret) {
> - RTE_LOG(DEBUG, VHOST_CONFIG, "IOTLB pool empty, evict one
> entry\n");
> - vhost_user_iotlb_cache_random_evict(vq);
> + RTE_LOG(DEBUG, VHOST_CONFIG, "IOTLB pool empty, clear
> entries\n");
Maybe we should use the same log level for both cases?
Currently, the first one is INFO, and this one is DEBUG.
> + if (!TAILQ_EMPTY(&vq->iotlb_list))
> + vhost_user_iotlb_cache_random_evict(vq);
> + else
> + vhost_user_iotlb_pending_remove_all(vq);
The IOTLB entry will be invalidated explicitly if it's
unmapped in the frontend. So all the IOTLB entries in
IOTLB cache are supposed to be valid. So I think maybe
it's better to always prefer to free memory from IOTLB
pending list. Something like:
if (TAILQ_EMPTY(&vq->iotlb_list))
vhost_user_iotlb_pending_remove_all(vq);
else if (TAILQ_EMPTY(&vq->iotlb_pending_list))
vhost_user_iotlb_cache_random_evict(vq);
else
vhost_user_iotlb_pending_random_evict(vq);
Besides, in __vhost_iova_to_vva():
uint64_t
__vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint64_t iova, uint64_t size, uint8_t perm)
{
uint64_t vva, tmp_size;
if (unlikely(!size))
return 0;
tmp_size = size;
vva = vhost_user_iotlb_cache_find(vq, iova, &tmp_size, perm);
if (tmp_size == size)
return vva;
if (!vhost_user_iotlb_pending_miss(vq, iova + tmp_size, perm)) {
/*
* iotlb_lock is read-locked for a full burst,
* but it only protects the iotlb cache.
* In case of IOTLB miss, we might block on the socket,
* which could cause a deadlock with QEMU if an IOTLB update
* is being handled. We can safely unlock here to avoid it.
*/
vhost_user_iotlb_rd_unlock(vq);
vhost_user_iotlb_pending_insert(vq, iova + tmp_size, perm);
vhost_user_iotlb_miss(dev, iova + tmp_size, perm);
The vhost_user_iotlb_miss() may fail. If it fails,
the inserted pending entry should be removed from
the pending list.
Best regards,
Tiwei Bie
