netdev - Re: [PATCH bpf-next V2 0/7] xdp: Allow BPF to set RX hints for XDP

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Message-ID: <20250801134045.4344cb44@kernel.org>
Date: Fri, 1 Aug 2025 13:40:45 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Lorenzo Bianconi <lorenzo@...nel.org>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>, Stanislav Fomichev
 <stfomichev@...il.com>, bpf@...r.kernel.org, netdev@...r.kernel.org, Alexei
 Starovoitov <ast@...nel.org>, Daniel Borkmann <borkmann@...earbox.net>,
 Eric Dumazet <eric.dumazet@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, sdf@...ichev.me,
 kernel-team@...udflare.com, arthur@...hurfabre.com, jakub@...udflare.com,
 Jesse Brandeburg <jbrandeburg@...udflare.com>
Subject: Re: [PATCH bpf-next V2 0/7] xdp: Allow BPF to set RX hints for
 XDP_REDIRECTed packets

On Thu, 31 Jul 2025 23:18:12 +0200 Lorenzo Bianconi wrote:
> IIUC the 'set' proposal (please correct me if I am wrong), the eBPF program
> running on the NIC that is receiving the packet from the wire is supposed
> to set (or update) the hw metadata info (e.g. RX HASH or RX checksum) in
> the RX DMA descriptor associated to the packet to be successively consumed.
> Am I right?

I was thinking of doing the SET on the veth side. Basically the
metadata has to be understood by the stack only at the xdp->skb
transition point. So we can delay the SET until that moment, carrying
the information in program-specific format.