[PATCH net] virtio-net: fix for skb_over_panic inside big mode

[PATCH net] virtio-net: fix for skb_over_panic inside big mode

[Michael S. Tsirkin]

From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

commit 126285651b7f ("Merge ra.kernel.org:/pub/scm/linux/kernel/git/netdev/net")
accidentally reverted the effect of
commit 1a8024239da ("virtio-net: fix for skb_over_panic inside big mode")
on drivers/net/virtio_net.c

As a result, users of crosvm (which is using large packet mode)
are experiencing crashes with 5.14-rc1 and above that do not
occur with 5.13.

Crash trace:

[   61.346677] skbuff: skb_over_panic: text:ffffffff881ae2c7 len:3762 put:3762 head:ffff8a5ec8c22000 data:ffff8a5ec8c22010 tail:0xec2 end:0xec0 dev:<NULL>
[   61.369192] kernel BUG at net/core/skbuff.c:111!
[   61.372840] invalid opcode: 0000 [#1] SMP PTI
[   61.374892] CPU: 5 PID: 0 Comm: swapper/5 Not tainted 5.14.0-rc1 linux-v5.14-rc1-for-mesa-ci.tar.bz2 #1
[   61.376450] Hardware name: ChromiumOS crosvm, BIOS 0

..

[   61.393635] Call Trace:
[   61.394127]  <IRQ>
[   61.394488]  skb_put.cold+0x10/0x10
[   61.395095]  page_to_skb+0xf7/0x410
[   61.395689]  receive_buf+0x81/0x1660
[   61.396228]  ? netif_receive_skb_list_internal+0x1ad/0x2b0
[   61.397180]  ? napi_gro_flush+0x97/0xe0
[   61.397896]  ? detach_buf_split+0x67/0x120
[   61.398573]  virtnet_poll+0x2cf/0x420
[   61.399197]  __napi_poll+0x25/0x150
[   61.399764]  net_rx_action+0x22f/0x280
[   61.400394]  __do_softirq+0xba/0x257
[   61.401012]  irq_exit_rcu+0x8e/0xb0
[   61.401618]  common_interrupt+0x7b/0xa0
[   61.402270]  </IRQ>

See
https://lore.kernel.org/r/5edaa2b7c2fe4abd0347b8454b2ac032b6694e2c.camel%40collabora.com
for the report.

Apply the original 1a8024239da ("virtio-net: fix for skb_over_panic inside big mode")
again, the original logic still holds:

In virtio-net's large packet mode, there is a hole in the space behind
buf.

    hdr_padded_len - hdr_len

We must take this into account when calculating tailroom.

Cc: Greg KH <gregkh@linuxfoundation.org>
Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
Fixes: 126285651b7f ("Merge ra.kernel.org:/pub/scm/linux/kernel/git/netdev/net")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Reported-by: Corentin Noël <corentin.noel@collabora.com>
Tested-by: Corentin Noël <corentin.noel@collabora.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

David, I think we need this in stable, too.

 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 096c2ac6b7a6..6b0812f44bbf 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -406,7 +406,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
 	 */
 	truesize = headroom ? PAGE_SIZE : truesize;
-	tailroom = truesize - len - headroom;
+	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
 	buf = p - headroom;
 
 	len -= hdr_len;
-- 
MST

Re: [PATCH net] virtio-net: fix for skb_over_panic inside big mode

[Jason Wang]

On Sat, Oct 9, 2021 at 5:18 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>
> commit 126285651b7f ("Merge ra.kernel.org:/pub/scm/linux/kernel/git/netdev/net")
> accidentally reverted the effect of
> commit 1a8024239da ("virtio-net: fix for skb_over_panic inside big mode")
> on drivers/net/virtio_net.c
>
> As a result, users of crosvm (which is using large packet mode)
> are experiencing crashes with 5.14-rc1 and above that do not
> occur with 5.13.
>
> Crash trace:
>
> [   61.346677] skbuff: skb_over_panic: text:ffffffff881ae2c7 len:3762 put:3762 head:ffff8a5ec8c22000 data:ffff8a5ec8c22010 tail:0xec2 end:0xec0 dev:<NULL>
> [   61.369192] kernel BUG at net/core/skbuff.c:111!
> [   61.372840] invalid opcode: 0000 [#1] SMP PTI
> [   61.374892] CPU: 5 PID: 0 Comm: swapper/5 Not tainted 5.14.0-rc1 linux-v5.14-rc1-for-mesa-ci.tar.bz2 #1
> [   61.376450] Hardware name: ChromiumOS crosvm, BIOS 0
>
> ..
>
> [   61.393635] Call Trace:
> [   61.394127]  <IRQ>
> [   61.394488]  skb_put.cold+0x10/0x10
> [   61.395095]  page_to_skb+0xf7/0x410
> [   61.395689]  receive_buf+0x81/0x1660
> [   61.396228]  ? netif_receive_skb_list_internal+0x1ad/0x2b0
> [   61.397180]  ? napi_gro_flush+0x97/0xe0
> [   61.397896]  ? detach_buf_split+0x67/0x120
> [   61.398573]  virtnet_poll+0x2cf/0x420
> [   61.399197]  __napi_poll+0x25/0x150
> [   61.399764]  net_rx_action+0x22f/0x280
> [   61.400394]  __do_softirq+0xba/0x257
> [   61.401012]  irq_exit_rcu+0x8e/0xb0
> [   61.401618]  common_interrupt+0x7b/0xa0
> [   61.402270]  </IRQ>
>
> See
> https://lore.kernel.org/r/5edaa2b7c2fe4abd0347b8454b2ac032b6694e2c.camel%40collabora.com
> for the report.
>
> Apply the original 1a8024239da ("virtio-net: fix for skb_over_panic inside big mode")
> again, the original logic still holds:
>
> In virtio-net's large packet mode, there is a hole in the space behind
> buf.
>
>     hdr_padded_len - hdr_len
>
> We must take this into account when calculating tailroom.
>
> Cc: Greg KH <gregkh@linuxfoundation.org>
> Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
> Fixes: 126285651b7f ("Merge ra.kernel.org:/pub/scm/linux/kernel/git/netdev/net")
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Reported-by: Corentin Noël <corentin.noel@collabora.com>
> Tested-by: Corentin Noël <corentin.noel@collabora.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---

Acked-by: Jason Wang <jasowang@redhat.com>

>
> David, I think we need this in stable, too.
>
>  drivers/net/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 096c2ac6b7a6..6b0812f44bbf 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -406,7 +406,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>          * add_recvbuf_mergeable() + get_mergeable_buf_len()
>          */
>         truesize = headroom ? PAGE_SIZE : truesize;
> -       tailroom = truesize - len - headroom;
> +       tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
>         buf = p - headroom;
>
>         len -= hdr_len;
> --
> MST
>

Re: [PATCH net] virtio-net: fix for skb_over_panic inside big mode

[Jason Wang]

在 2021/6/4 上午11:05, Xuan Zhuo 写道:
> On Fri, 4 Jun 2021 11:00:25 +0800, Jason Wang <jasowang@redhat.com> wrote:
>> 在 2021/6/4 上午10:30, Xuan Zhuo 写道:
>>> On Fri, 4 Jun 2021 10:28:41 +0800, Jason Wang <jasowang@redhat.com> wrote:
>>>> 在 2021/6/4 上午1:09, Xuan Zhuo 写道:
>>>>> In virtio-net's large packet mode, there is a hole in the space behind
>>>>> buf.
>>>> before the buf actually or behind the vnet header?
>>>>
>>>>
>>>>>        hdr_padded_len - hdr_len
>>>>>
>>>>> We must take this into account when calculating tailroom.
>>>>>
>>>>> [   44.544385] skb_put.cold (net/core/skbuff.c:5254 (discriminator 1) net/core/skbuff.c:5252 (discriminator 1))
>>>>> [   44.544864] page_to_skb (drivers/net/virtio_net.c:485) [   44.545361] receive_buf (drivers/net/virtio_net.c:849 drivers/net/virtio_net.c:1131)
>>>>> [   44.545870] ? netif_receive_skb_list_internal (net/core/dev.c:5714)
>>>>> [   44.546628] ? dev_gro_receive (net/core/dev.c:6103)
>>>>> [   44.547135] ? napi_complete_done (./include/linux/list.h:35 net/core/dev.c:5867 net/core/dev.c:5862 net/core/dev.c:6565)
>>>>> [   44.547672] virtnet_poll (drivers/net/virtio_net.c:1427 drivers/net/virtio_net.c:1525)
>>>>> [   44.548251] __napi_poll (net/core/dev.c:6985)
>>>>> [   44.548744] net_rx_action (net/core/dev.c:7054 net/core/dev.c:7139)
>>>>> [   44.549264] __do_softirq (./arch/x86/include/asm/jump_label.h:19 ./include/linux/jump_label.h:200 ./include/trace/events/irq.h:142 kernel/softirq.c:560)
>>>>> [   44.549762] irq_exit_rcu (kernel/softirq.c:433 kernel/softirq.c:637 kernel/softirq.c:649)
>>>>> [   44.551384] common_interrupt (arch/x86/kernel/irq.c:240 (discriminator 13))
>>>>> [   44.551991] ? asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
>>>>> [   44.552654] asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
>>>>>
>>>>> Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
>>>>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>>>>> Reported-by: Corentin Noël <corentin.noel@collabora.com>
>>>>> Tested-by: Corentin Noël <corentin.noel@collabora.com>
>>>>> ---
>>>>>     drivers/net/virtio_net.c | 2 +-
>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>>> index fa407eb8b457..78a01c71a17c 100644
>>>>> --- a/drivers/net/virtio_net.c
>>>>> +++ b/drivers/net/virtio_net.c
>>>>> @@ -406,7 +406,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>>>>     	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
>>>>>     	 */
>>>>>     	truesize = headroom ? PAGE_SIZE : truesize;
>>>>> -	tailroom = truesize - len - headroom;
>>>>> +	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
>>>> The patch looks correct and I saw it has been merged.
>>>>
>>>> But I prefer to do that in receive_big() instead of here.
>>>>
>>>> Thanks
>>> How?
>>>
>>> change truesize or headroom?
>>>
>>> I didn't find a good way. Do you have a good way?
>>
>> Something like the following? The API is designed to let the caller to
>> pass a correct headroom instead of figure it out by itself.
>>
>>           struct sk_buff *skb =
>>                   page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0,
>> hdr_padded_len - hdr_len);
>>
>> Thanks
>
> This line may be affected.
>
> 	buf = p - headroom;
>
> In my opinion, this changes the semantics of the original headroom. The meaning
> of headroom in big mode and merge mode has become different. The more confusing
> problem is that the parameters of page_to_skb() are getting more and more
> chaotic.  So I wrote the previous patch. Of course, I understand your concern.
> This patch may bring Here are more questions, although I did a lot of tests.
>
> 	"virtio-net: Refactor the code related to page_to_skb"
>
> But I hope that our code development direction is as close to what this patch
> realizes. I hope that the meaning of the parameters can be more clear.


So I don't object to this method, but as I replied, it's better to do 
some benchmark to see if it introduces any regression


>
> Do you think this is ok?


Looks ok, but if we decide to go with your approach, it can be squashed 
into that patch.

Thanks


>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 78a01c71a17c..6d62bb45a188 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -380,34 +380,20 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>   				   struct page *page, unsigned int offset,
>   				   unsigned int len, unsigned int truesize,
>   				   bool hdr_valid, unsigned int metasize,
> -				   unsigned int headroom)
> +				   int tailroom, char *buf,
> +				   unsigned int hdr_padded_len)
>   {
>   	struct sk_buff *skb;
>   	struct virtio_net_hdr_mrg_rxbuf *hdr;
> -	unsigned int copy, hdr_len, hdr_padded_len;
> +	unsigned int copy, hdr_len;
>   	struct page *page_to_free = NULL;
> -	int tailroom, shinfo_size;
> -	char *p, *hdr_p, *buf;
> +	int shinfo_size;
> +	char *p, *hdr_p;
>
>   	p = page_address(page) + offset;
>   	hdr_p = p;
>
>   	hdr_len = vi->hdr_len;
> -	if (vi->mergeable_rx_bufs)
> -		hdr_padded_len = sizeof(*hdr);
> -	else
> -		hdr_padded_len = sizeof(struct padded_vnet_hdr);
> -
> -	/* If headroom is not 0, there is an offset between the beginning of the
> -	 * data and the allocated space, otherwise the data and the allocated
> -	 * space are aligned.
> -	 *
> -	 * Buffers with headroom use PAGE_SIZE as alloc size, see
> -	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
> -	 */
> -	truesize = headroom ? PAGE_SIZE : truesize;
> -	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
> -	buf = p - headroom;
>
>   	len -= hdr_len;
>   	offset += hdr_padded_len;
> @@ -492,6 +478,51 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>   	return skb;
>   }
>
> +static struct sk_buff *merge_page_to_skb(struct virtnet_info *vi,
> +					 struct receive_queue *rq,
> +					 struct page *page, unsigned int offset,
> +					 unsigned int len, unsigned int truesize,
> +					 bool hdr_valid, unsigned int metasize,
> +					 unsigned int headroom)
> +{
> +	int tailroom;
> +	char *buf;
> +
> +	/* If headroom is not 0, there is an offset between the beginning of the
> +	 * data and the allocated space, otherwise the data and the allocated
> +	 * space are aligned.
> +	 *
> +	 * Buffers with headroom use PAGE_SIZE as alloc size, see
> +	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
> +	 */
> +	truesize = headroom ? PAGE_SIZE : truesize;
> +	tailroom = truesize - len - headroom;
> +	buf = page_address(page) + offset - headroom;
> +
> +	page_to_skb(vi, rq, page, offset, len, truesize, hdr_valid, metasize,
> +		    tailroom, buf, sizeof(struct virtio_net_hdr_mrg_rxbuf))
> +
> +}
> +
> +static struct sk_buff *big_page_to_skb(struct virtnet_info *vi,
> +				       struct receive_queue *rq,
> +				       struct page *page, unsigned int offset,
> +				       unsigned int len, unsigned int truesize,
> +				       bool hdr_valid, unsigned int metasize,
> +				       unsigned int headroom)
> +{
> +	char *p = page_address(page);
> +	int hold;
> +	int tailroom;
> +
> +	hold = sizeof(struct padded_vnet_hdr) - vi->hdr_len;
> +
> +	tailroom = truesize - len - headroom - hold;
> +
> +	page_to_skb(vi, rq, page, offset, len, truesize, hdr_valid, metasize,
> +		    tailroom, p, sizeof(struct padded_vnet_hdr));
> +}
> +
>   static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>   				   struct send_queue *sq,
>   				   struct xdp_frame *xdpf)
>
>
>>
>>> Thanks.
>>>
>>>>
>>>>>     	buf = p - headroom;
>>>>>
>>>>>     	len -= hdr_len;

Re: [PATCH net] virtio-net: fix for skb_over_panic inside big mode

[Jason Wang]

在 2021/6/4 上午10:30, Xuan Zhuo 写道:
> On Fri, 4 Jun 2021 10:28:41 +0800, Jason Wang <jasowang@redhat.com> wrote:
>> 在 2021/6/4 上午1:09, Xuan Zhuo 写道:
>>> In virtio-net's large packet mode, there is a hole in the space behind
>>> buf.
>>
>> before the buf actually or behind the vnet header?
>>
>>
>>>       hdr_padded_len - hdr_len
>>>
>>> We must take this into account when calculating tailroom.
>>>
>>> [   44.544385] skb_put.cold (net/core/skbuff.c:5254 (discriminator 1) net/core/skbuff.c:5252 (discriminator 1))
>>> [   44.544864] page_to_skb (drivers/net/virtio_net.c:485) [   44.545361] receive_buf (drivers/net/virtio_net.c:849 drivers/net/virtio_net.c:1131)
>>> [   44.545870] ? netif_receive_skb_list_internal (net/core/dev.c:5714)
>>> [   44.546628] ? dev_gro_receive (net/core/dev.c:6103)
>>> [   44.547135] ? napi_complete_done (./include/linux/list.h:35 net/core/dev.c:5867 net/core/dev.c:5862 net/core/dev.c:6565)
>>> [   44.547672] virtnet_poll (drivers/net/virtio_net.c:1427 drivers/net/virtio_net.c:1525)
>>> [   44.548251] __napi_poll (net/core/dev.c:6985)
>>> [   44.548744] net_rx_action (net/core/dev.c:7054 net/core/dev.c:7139)
>>> [   44.549264] __do_softirq (./arch/x86/include/asm/jump_label.h:19 ./include/linux/jump_label.h:200 ./include/trace/events/irq.h:142 kernel/softirq.c:560)
>>> [   44.549762] irq_exit_rcu (kernel/softirq.c:433 kernel/softirq.c:637 kernel/softirq.c:649)
>>> [   44.551384] common_interrupt (arch/x86/kernel/irq.c:240 (discriminator 13))
>>> [   44.551991] ? asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
>>> [   44.552654] asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
>>>
>>> Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
>>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>>> Reported-by: Corentin Noël <corentin.noel@collabora.com>
>>> Tested-by: Corentin Noël <corentin.noel@collabora.com>
>>> ---
>>>    drivers/net/virtio_net.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index fa407eb8b457..78a01c71a17c 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -406,7 +406,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>>    	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
>>>    	 */
>>>    	truesize = headroom ? PAGE_SIZE : truesize;
>>> -	tailroom = truesize - len - headroom;
>>> +	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
>>
>> The patch looks correct and I saw it has been merged.
>>
>> But I prefer to do that in receive_big() instead of here.
>>
>> Thanks
> How?
>
> change truesize or headroom?
>
> I didn't find a good way. Do you have a good way?


Something like the following? The API is designed to let the caller to 
pass a correct headroom instead of figure it out by itself.

         struct sk_buff *skb =
                 page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0, 
hdr_padded_len - hdr_len);

Thanks


>
> Thanks.
>
>>
>>
>>>    	buf = p - headroom;
>>>
>>>    	len -= hdr_len;

Re: [PATCH net] virtio-net: fix for skb_over_panic inside big mode

[Jason Wang]

在 2021/6/4 上午1:09, Xuan Zhuo 写道:
> In virtio-net's large packet mode, there is a hole in the space behind
> buf.


before the buf actually or behind the vnet header?


>
>      hdr_padded_len - hdr_len
>
> We must take this into account when calculating tailroom.
>
> [   44.544385] skb_put.cold (net/core/skbuff.c:5254 (discriminator 1) net/core/skbuff.c:5252 (discriminator 1))
> [   44.544864] page_to_skb (drivers/net/virtio_net.c:485) [   44.545361] receive_buf (drivers/net/virtio_net.c:849 drivers/net/virtio_net.c:1131)
> [   44.545870] ? netif_receive_skb_list_internal (net/core/dev.c:5714)
> [   44.546628] ? dev_gro_receive (net/core/dev.c:6103)
> [   44.547135] ? napi_complete_done (./include/linux/list.h:35 net/core/dev.c:5867 net/core/dev.c:5862 net/core/dev.c:6565)
> [   44.547672] virtnet_poll (drivers/net/virtio_net.c:1427 drivers/net/virtio_net.c:1525)
> [   44.548251] __napi_poll (net/core/dev.c:6985)
> [   44.548744] net_rx_action (net/core/dev.c:7054 net/core/dev.c:7139)
> [   44.549264] __do_softirq (./arch/x86/include/asm/jump_label.h:19 ./include/linux/jump_label.h:200 ./include/trace/events/irq.h:142 kernel/softirq.c:560)
> [   44.549762] irq_exit_rcu (kernel/softirq.c:433 kernel/softirq.c:637 kernel/softirq.c:649)
> [   44.551384] common_interrupt (arch/x86/kernel/irq.c:240 (discriminator 13))
> [   44.551991] ? asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
> [   44.552654] asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
>
> Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Reported-by: Corentin Noël <corentin.noel@collabora.com>
> Tested-by: Corentin Noël <corentin.noel@collabora.com>
> ---
>   drivers/net/virtio_net.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fa407eb8b457..78a01c71a17c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -406,7 +406,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>   	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
>   	 */
>   	truesize = headroom ? PAGE_SIZE : truesize;
> -	tailroom = truesize - len - headroom;
> +	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);


The patch looks correct and I saw it has been merged.

But I prefer to do that in receive_big() instead of here.

Thanks



>   	buf = p - headroom;
>   
>   	len -= hdr_len;

Re: [PATCH net] virtio-net: fix for skb_over_panic inside big mode

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Fri,  4 Jun 2021 01:09:01 +0800 you wrote:
> In virtio-net's large packet mode, there is a hole in the space behind
> buf.
> 
>     hdr_padded_len - hdr_len
> 
> We must take this into account when calculating tailroom.
> 
> [...]

Here is the summary with links:
  - [net] virtio-net: fix for skb_over_panic inside big mode
    https://git.kernel.org/netdev/net/c/1a8024239dac

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

[PATCH net] virtio-net: fix for skb_over_panic inside big mode

[Xuan Zhuo]

In virtio-net's large packet mode, there is a hole in the space behind
buf.

    hdr_padded_len - hdr_len

We must take this into account when calculating tailroom.

[   44.544385] skb_put.cold (net/core/skbuff.c:5254 (discriminator 1) net/core/skbuff.c:5252 (discriminator 1))
[   44.544864] page_to_skb (drivers/net/virtio_net.c:485) [   44.545361] receive_buf (drivers/net/virtio_net.c:849 drivers/net/virtio_net.c:1131)
[   44.545870] ? netif_receive_skb_list_internal (net/core/dev.c:5714)
[   44.546628] ? dev_gro_receive (net/core/dev.c:6103)
[   44.547135] ? napi_complete_done (./include/linux/list.h:35 net/core/dev.c:5867 net/core/dev.c:5862 net/core/dev.c:6565)
[   44.547672] virtnet_poll (drivers/net/virtio_net.c:1427 drivers/net/virtio_net.c:1525)
[   44.548251] __napi_poll (net/core/dev.c:6985)
[   44.548744] net_rx_action (net/core/dev.c:7054 net/core/dev.c:7139)
[   44.549264] __do_softirq (./arch/x86/include/asm/jump_label.h:19 ./include/linux/jump_label.h:200 ./include/trace/events/irq.h:142 kernel/softirq.c:560)
[   44.549762] irq_exit_rcu (kernel/softirq.c:433 kernel/softirq.c:637 kernel/softirq.c:649)
[   44.551384] common_interrupt (arch/x86/kernel/irq.c:240 (discriminator 13))
[   44.551991] ? asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
[   44.552654] asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)

Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Reported-by: Corentin Noël <corentin.noel@collabora.com>
Tested-by: Corentin Noël <corentin.noel@collabora.com>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fa407eb8b457..78a01c71a17c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -406,7 +406,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
 	 */
 	truesize = headroom ? PAGE_SIZE : truesize;
-	tailroom = truesize - len - headroom;
+	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
 	buf = p - headroom;
 
 	len -= hdr_len;
-- 
2.31.0