netdev - Re: [PATCH v6 net-next 13/13] mlx5: support BIG TCP packets

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Date:   Fri, 13 May 2022 10:04:21 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Saeed Mahameed <saeedm@...dia.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Alexander Duyck <alexanderduyck@...com>,
        Coco Li <lixiaoyan@...gle.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v6 net-next 13/13] mlx5: support BIG TCP packets

On Fri, 13 May 2022 06:05:36 -0700 Eric Dumazet wrote:
> The problem is that  skb_cow_head() can fail.
> 
> Really we have thought about this already.
> 
> A common helper for drivers is mostly unusable, you would have to
> pre-allocate a per TX-ring slot to store the headers.
> We would end up with adding complexity at queue creation/dismantle.
> 
> We could do that later, because some NICs do not inline the headers in
> TX descriptor, but instead request
> one mapped buffer for the headers part only.
> 
> BTW, I know Tariq already reviewed, the issue at hand is about
> CONFIG_FORTIFY which is blocking us.
> 
> This is why I was considering not submitting mlx5 change until Kees
> Cook and others come up with a solution.

We do have the solution, no?

commit 43213daed6d6 ("fortify: Provide a memcpy trap door for sharp
corners")