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. Cc: "Michael S. Tsirkin" <mst at redhat.com> Suggested-by: Huawei Xie <huawei.xie at intel.com> Signed-off-by: Yuanhan Liu <yuanhan.liu at linux.intel.com> Acked-by: "Michael S. Tsirkin" <mst at redhat.com> Acked-by: Huawei Xie <huawei.xie at intel.com> --- v2: log on packets resent for Tx and drop for Rx --- lib/librte_vhost/virtio-net.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/lib/librte_vhost/virtio-net.c b/lib/librte_vhost/virtio-net.c index 835ab3a..bd7e55e 100644 --- a/lib/librte_vhost/virtio-net.c +++ b/lib/librte_vhost/virtio-net.c @@ -561,6 +561,15 @@ vhost_set_vring_addr(int vid, struct vhost_vring_addr *addr) 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; LOG_DEBUG(VHOST_CONFIG, "(%d) mapped address desc: %p\n", -- 1.9.0