netdev - Re: [RFC bpf-next v1 3/7] bpf: Support pulling non-linear xdp data

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Message-ID: <20250825155813.763d2a59@kernel.org>
Date: Mon, 25 Aug 2025 15:58:13 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: Amery Hung <ameryhung@...il.com>, bpf@...r.kernel.org,
 netdev@...r.kernel.org, alexei.starovoitov@...il.com, andrii@...nel.org,
 daniel@...earbox.net, martin.lau@...nel.org, mohsin.bashr@...il.com,
 saeedm@...dia.com, tariqt@...dia.com, mbloch@...dia.com,
 maciej.fijalkowski@...el.com, kernel-team@...a.com
Subject: Re: [RFC bpf-next v1 3/7] bpf: Support pulling non-linear xdp data

On Mon, 25 Aug 2025 15:46:02 -0700 Stanislav Fomichev wrote:
> > > skb_frag_address can return NULL for unreadable frags.  
> > 
> > Is it safe to assume that drivers will ensure frags to be readable? It
> > seems at least mlx5 does.
> > 
> > I did a quick check and found other xdp kfuncs using
> > skb_frag_address() without checking the return.  
> 
> The unreadable frags will always be unredabale to the host. This is TCP
> device memory, the memory on the accelerators that is not mapped onto
> the CPU. Any attempts to read that memory should gracefully error out.
> 
> Can you also pls fix that other one? (not as part of the series should
> be ok)

But we don't support mixing XDP with unreadable mem today.
Is the concern just for future proofing?