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Date: Mon, 25 Aug 2025 15:58:13 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Stanislav Fomichev <stfomichev@gmail.com>
Cc: Amery Hung <ameryhung@gmail.com>, bpf@vger.kernel.org,
 netdev@vger.kernel.org, alexei.starovoitov@gmail.com, andrii@kernel.org,
 daniel@iogearbox.net, martin.lau@kernel.org, mohsin.bashr@gmail.com,
 saeedm@nvidia.com, tariqt@nvidia.com, mbloch@nvidia.com,
 maciej.fijalkowski@intel.com, kernel-team@meta.com
Subject: Re: [RFC bpf-next v1 3/7] bpf: Support pulling non-linear xdp data
Message-ID: <20250825155813.763d2a59@kernel.org>
In-Reply-To: <aKznqjd1aowjxJfK@mini-arch>
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	<aKzVsZ0D53rhOhQe@mini-arch>
	<CAMB2axOkPx=5vseNXbwQtHQTFhdur6OSZ-HbNPUciwBmubQa1w@mail.gmail.com>
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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?