From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DD7DB407570; Wed, 22 Jul 2026 18:35:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784745330; cv=none; b=tRTMdRrJR6MG1zvR+mb9WlfRPq7HXQRXofRWH70SY0ivSGQolIK9DSeFvQh8oUP9UNkoqGWe54KuxOkEVneomJIez2CkqyTILDs9vyKIsvY/43GycyrPnPXxR9LInoxiWNG4padM5TnDovQwog114XSkSmOzbDX65N2fiBAISsg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784745330; c=relaxed/simple; bh=dSlnlKe07hlOR23uhYPBh8ZTHKH8iB8wQID+iaO+xXo=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Hbttmt6bzJ+qz87tSjj9nn9pSwITKXiQZuChare3AfCLELk6YzoNowcBIfUZNvMpDcbcVzmjmwCBwiAlCkN2Nk+C1AWS5Hs6Tm+evZGXOA0r3V1OYHgsxbhL7Zby5QY7SXftqJk10+onzvZraiqUPUZAv7sabBzImeGGJJjLvVk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a6LTxb6M; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="a6LTxb6M" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2C4751F00A3A; Wed, 22 Jul 2026 18:35:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784745328; bh=670ICVCxpkbIIsTKMOsa+I+z+C4FgJRDQNs6RF7SdGI=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=a6LTxb6Me6mG2aUNvx62hRLaJopZgj2ogTsG8vH+9nTrF7phHbWJSmGpvev0Mxvvt 3c8U84ok5cF/v+rxZT6PsnyNEZnEti27oSLMZ9CjBWQ14jQOM+KjpEdYKOjUnyscea bD75r9/q7UDGNM7PAAcphCZ39vlipGyeAoYzQ+fLUEH8VNtac1NbFbz50FqsCzoChy yx4Eo3Q4/fyiLdyQPCRVfHlVSFX0DNSbXI2sqB0ToGN4AG0xOBFEB1dtrm4HHoicKc Z1YlaRTqCujzVsoH4VJYq92fziN8WHTbT/wc//wfZW0o1XGNXS+uwZmLenI7DcjKu+ iVpXtEUew6/mw== Date: Wed, 22 Jul 2026 11:35:25 -0700 From: Jakub Kicinski To: Stanislav Fomichev Cc: Lorenzo Bianconi , Donald Hunter , "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Andrew Lunn , Tony Nguyen , Przemek Kitszel , Alexander Lobakin , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , Shuah Khan , Maciej Fijalkowski , Jonathan Corbet , Shuah Khan , Kumar Kartikeya Dwivedi , Emil Tsalapatis , Vladimir Vdovin , Jakub Sitnicki , netdev@vger.kernel.org, bpf@vger.kernel.org, intel-wired-lan@lists.osuosl.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH bpf-next v5 8/8] selftests: net: add test for XDP_PASS skb checksum invalidation Message-ID: <20260722113525.34092660@kernel.org> In-Reply-To: References: <20260715-bpf-xdp-meta-rxcksum-v5-0-623d5c0d0ab7@kernel.org> <20260715-bpf-xdp-meta-rxcksum-v5-8-623d5c0d0ab7@kernel.org> <20260721082728.74142e6c@kernel.org> <20260721183256.6f49d6e1@kernel.org> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 22 Jul 2026 11:00:07 -0700 Stanislav Fomichev wrote: > > > This is about current drivers that only report UNNECESSARY with xdp: the xdp > > > prog has to maintain in-packet checksum if it changes the payload. I think > > > it's a fair assumption? > > > > What about decap? If we decap the header that device validated > > as UNNECESSARY there's no possibility of maintaining the checksum > > (by which IIUC you mean correcting it in along the payload changes). > > > > I think we'd need some API to "decrement the csum level" ? > > Or some heuristic in the drivers to decrement if the head moved > > by at least len(IP+UDP) into the packet ? > > True :-/ I guess one more case to document? What would we be documenting? That it's a known bug and we have no idea how to address it? Or am I missing something? Again: .. the ask was to sketch out the plan of explicitly updating/invalidating the checksum even if we don't implement it today