On Mon, Apr 4, 2016 at 1:05 PM, Yuanhan Liu <yuanhan.liu at linux.intel.com> wrote:
> On Mon, Apr 04, 2016 at 03:13:37PM +0200, Thomas Monjalon wrote: > > Huawei, Yuanhan, any comment? > > > > 2016-03-31 13:01, Rich Lane: > > > vq->vq_ring.desc[i + mid_idx].next = i; > > > vq->vq_ring.desc[i + mid_idx].addr = > > > - vq->virtio_net_hdr_mem + > > > - i * vq->hw->vtnet_hdr_size; > > > + vq->virtio_net_hdr_mem; > > I could be wrong, but this looks like a special case when i == 0, > which is by no way that zeroed memory is guaranteed? Huawei, do > you have time to check this patch? This bug exists because the type of the objects pointed to by virtio_net_hdr_mem changed in 6dc5de3a (virtio: use indirect ring elements), but because it isn't a C pointer the compiler didn't catch the type mismatch. We could also fix it with: vq->virtio_net_hdr_mem + i * sizeof(struct virtio_tx_region) + offsetof(struct virtio_tx_region, tx_hdr) Given that tx_hdr is the first member in struct virtio_tx_region, and using a single header optimizes cache use, that simplifies to the code in my patch. The virtio-net header is never written to by simple TX so it remains zeroed. I can respin the patch using offsetof if that's preferred. Note that right now virtio simple TX is broken with DPDK vhost due to the flood of error messages.