Re: [dpdk-dev] [PATCH] virtio: fix packet corruption

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

Hi Oliver,

> -----Original Message-----
> From: Olivier Matz [mailto:olivier.matz@6wind.com]
> Sent: Tuesday, July 19, 2016 10:00 PM
> To: Tan, Jianfeng; dev@dpdk.org; Xie, Huawei; yuanhan.liu@linux.intel.com
> Subject: Re: [PATCH] virtio: fix packet corruption
> 
> Hi,
> 
> On 07/19/2016 03:57 PM, Tan, Jianfeng wrote:
> >
> >
> >> -----Original Message-----
> >> From: Olivier Matz [mailto:olivier.matz@6wind.com]
> >> Sent: Tuesday, July 19, 2016 9:11 PM
> >> To: Tan, Jianfeng; dev@dpdk.org; Xie, Huawei;
> yuanhan.liu@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@6wind.com]
> >>>> Sent: Tuesday, July 19, 2016 8:32 PM
> >>>> To: dev@dpdk.org; Tan, Jianfeng; Xie, Huawei;
> >> yuanhan.liu@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.

Thanks for clarification. Looks good to me.

Acked-by: Jianfeng Tan <jianfeng.tan@intel.com>