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

[Olivier Matz <olivier.matz@6wind.com>]

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.

I did not include the test plan because it relies on patch that are not
submitted yet (offload patches, they will be upstreamed very soon). It
is a quite simple test case with testpmd.

Regards,
Olivier