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Date:   Mon, 26 Dec 2016 10:34:39 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     John Fastabend <john.fastabend@...il.com>, mst@...hat.com,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     john.r.fastabend@...el.com
Subject: Re: [PATCH net 4/9] virtio-net: correctly handle XDP_PASS for
 linearized packets



On 2016年12月23日 23:57, John Fastabend wrote:
> On 16-12-23 06:37 AM, Jason Wang wrote:
>> When XDP_PASS were determined for linearized packets, we try to get
>> new buffers in the virtqueue and build skbs from them. This is wrong,
>> we should create skbs based on existed buffers instead. Fixing them by
>> creating skb based on xdp_page.
>>
>> With this patch "ping 192.168.100.4 -s 3900 -M do" works for XDP_PASS.
>>
>> Cc: John Fastabend <john.r.fastabend@...el.com>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>   drivers/net/virtio_net.c | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 58ad40e..470293e 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -578,8 +578,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>   		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
>>   		switch (act) {
>>   		case XDP_PASS:
>> -			if (unlikely(xdp_page != page))
>> -				__free_pages(xdp_page, 0);
>> +			/* We can only create skb based on xdp_page. */
>> +			if (unlikely(xdp_page != page)) {
>> +				rcu_read_unlock();
>> +				put_page(page);
>> +				head_skb = page_to_skb(vi, rq, xdp_page,
>> +						       0, len, PAGE_SIZE);
>> +				return head_skb;
>> +			}
>>   			break;
>>   		case XDP_TX:
>>   			if (unlikely(xdp_page != page))
>>
> Great thanks. This was likely working before because of the memory
> leak fixed in 3/9.

Looks not, without this and 3/9 the code will try to get buffers and 
build skb for a new packet instead of existed buffers.

Thanks

>
> Acked-by: John Fastabend <john.r.fastabend@...el.com>

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