linux-kernel - Re: [PATCH net v2] net: ethernet: ti: am65-cpsw-nuss: Fix skb size by accounting for skb_shared

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Message-ID: <95d7cf5c-6995-401a-b9de-08b82482b175@ti.com>
Date: Thu, 3 Jul 2025 10:53:37 +0530
From: Chintan Vankar <c-vankar@...com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <andrew+netdev@...n.ch>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <pabeni@...hat.com>, <rogerq@...nel.org>, <horms@...nel.org>,
        <mwalle@...nel.org>, <jacob.e.keller@...el.com>, <jpanis@...libre.com>,
        <s-vadapalli@...com>, <danishanwar@...com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v2] net: ethernet: ti: am65-cpsw-nuss: Fix skb size by
 accounting for skb_shared_info

Hello Jakub,

On 28/06/25 05:38, Jakub Kicinski wrote:
> On Thu, 26 Jun 2025 10:42:26 +0530 Chintan Vankar wrote:
>> While transitioning from netdev_alloc_ip_align() to build_skb(), memory
>> for the "skb_shared_info" member of an "skb" was not allocated. Fix this
>> by including sizeof(skb_shared_info) in the packet length during
>> allocation.
>>
>> Fixes: 8acacc40f733 ("net: ethernet: ti: am65-cpsw: Add minimal XDP support")
>> Signed-off-by: Chintan Vankar <c-vankar@...com>
>> ---
>>
>> This patch is based on the commit '9caca6ac0e26' of origin/main branch of
>> Linux-net repository.
>>
>> Link to v1:
>> https://lore.kernel.org/r/598f9e77-8212-426b-97ab-427cb8bd4910@ti.com/
>>
>> Changes from v1 to v2:
>> - Updated commit message and code change as suggested by Siddharth
>>    Vadapalli.
>>
>>   drivers/net/ethernet/ti/am65-cpsw-nuss.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
>> index f20d1ff192ef..67fef2ea4900 100644
>> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
>> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
>> @@ -856,7 +856,7 @@ static struct sk_buff *am65_cpsw_build_skb(void *page_addr,
>>   {
>>   	struct sk_buff *skb;
>>   
>> -	len += AM65_CPSW_HEADROOM;
>> +	len += AM65_CPSW_HEADROOM + SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>>   
>>   	skb = build_skb(page_addr, len);
> 
> Looks to me like each packet is placed in a full page, isn't it?
> If that's the case the correct value for "buffer size" is PAGE_SIZE


Thanks for reviewing the patch and pointing this out. Since the maximum
packet size received from the wire is AM65_CPSW_MAX_PACKET_SIZE that is
2024 Bytes, after adding headroom and tailroom, the total Bytes will
remain below the minimum page size available that is 4096, it is better
to use PAGE_SIZE.

Regards,
Chintan.