Hi, On 07/19/2016 03:57 PM, Tan, Jianfeng wrote: > > >> -----Original Message----- >> From: Olivier Matz [mailto:olivier.matz at 6wind.com] >> Sent: Tuesday, July 19, 2016 9:11 PM >> To: Tan, Jianfeng; dev at dpdk.org; Xie, Huawei; yuanhan.liu at >> linux.intel.com >> Subject: Re: [PATCH] virtio: fix packet corruption >> >> Hi Jianfeng, >> >> On 07/19/2016 03:03 PM, Tan, Jianfeng wrote: >>> Hi Oliver, >>> >>>> -----Original Message----- >>>> From: Olivier Matz [mailto:olivier.matz at 6wind.com] >>>> Sent: Tuesday, July 19, 2016 8:32 PM >>>> To: dev at dpdk.org; Tan, Jianfeng; Xie, Huawei; >> yuanhan.liu at linux.intel.com >>>> Subject: [PATCH] virtio: fix packet corruption >>>> >>>> The support of virtio-user changed the way the mbuf dma address is >>>> retrieved, using a physical address in case of virtio-pci and a virtual >>>> address in case of virtio-user. >>>> >>>> This change introduced some possible memory corruption in packets, >>>> replacing: >>>> m->buf_physaddr + RTE_PKTMBUF_HEADROOM >>>> by: >>>> m->buf_physaddr + m->data_off (through a macro) >>>> >>>> This patch fixes this issue, restoring the original behavior. >>> >>> Could you be more specific on why we cannot use m->data_off here? >> >> There is no guarantee that m->data_off == RTE_PKTMBUF_HEADROOM here >> as >> virtqueue_enqueue_recv_refill() is called on a mbuf that is just >> allocated with rte_mbuf_raw_alloc(). An alternative would be to set >> data_off to RTE_PKTMBUF_HEADROOM, but as it's a fix and we are close to >> the release, I prefered to restore the initial behavior. > > Oh yes, gotcha. > > But if we do not set data_off properly, it's still buggy when others consume > these mbufs, right? >
This is done later in virtio_recv_pkts*() functions, one the host has written the data in the mbuf.
