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vhost: workaround stale vring base

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When DPDK app crashes (or quits, or gets killed), a restart of DPDK
app would get stale vring base from QEMU. That would break the kernel
virtio net completely, making it non-work any more, unless a driver
reset is done.

So, instead of getting the stale vring base from QEMU, Huawei suggested
we could get a much saner (and may not the most accurate) vring base
from used->idx. That would work because:

- there is a memory barrier between updating used ring entries and
  used->idx. So, even though we crashed at updating the used ring
  entries, it will not cause any issue, as the guest driver will not
  process those stale used entries, for used-idx is not updated yet.

- DPDK process vring in order, that means a crash may just lead some
  packet retransmission for Tx and drop for Rx.

Suggested-by: Huawei Xie <huawei.xie@intel.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Huawei Xie <huawei.xie@intel.com>
This commit is contained in:
Yuanhan Liu 2016-05-07 06:04:05 +08:00
parent e623e0c6d8
commit 0823c1cb0a
1 changed files with 9 additions and 0 deletions
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9
lib/librte_vhost/virtio-net.c
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@ -561,6 +561,15 @@ vhost_set_vring_addr(int vid, struct vhost_vring_addr *addr)
return -1; return -1;
} }
if (vq->last_used_idx != vq->used->idx) {
RTE_LOG(WARNING, VHOST_CONFIG,
"last_used_idx (%u) and vq->used->idx (%u) mismatches; "
"some packets maybe resent for Tx and dropped for Rx\n",
vq->last_used_idx, vq->used->idx);
vq->last_used_idx = vq->used->idx;
vq->last_used_idx_res = vq->used->idx;
}
vq->log_guest_addr = addr->log_guest_addr; vq->log_guest_addr = addr->log_guest_addr;
LOG_DEBUG(VHOST_CONFIG, "(%d) mapped address desc: %p\n", LOG_DEBUG(VHOST_CONFIG, "(%d) mapped address desc: %p\n",