netdev - Re: [PATCH bpf-next v4 12/21] xdp: Add checksum hint

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Date: Fri, 28 Jul 2023 14:53:40 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Larysa Zaremba <larysa.zaremba@...el.com>
Cc: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
	andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
	yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
	sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
	David Ahern <dsahern@...il.com>, Jakub Kicinski <kuba@...nel.org>,
	Willem de Bruijn <willemb@...gle.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Anatoly Burakov <anatoly.burakov@...el.com>,
	Alexander Lobakin <alexandr.lobakin@...el.com>,
	Magnus Karlsson <magnus.karlsson@...il.com>,
	Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
	netdev@...r.kernel.org,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Simon Horman <simon.horman@...igine.com>
Subject: Re: [PATCH bpf-next v4 12/21] xdp: Add checksum hint

On Fri, Jul 28, 2023 at 07:39:14PM +0200, Larysa Zaremba wrote:
>  
> +union xdp_csum_info {
> +	/* Checksum referred to by ``csum_start + csum_offset`` is considered
> +	 * valid, but was never calculated, TX device has to do this,
> +	 * starting from csum_start packet byte.
> +	 * Any preceding checksums are also considered valid.
> +	 * Available, if ``status == XDP_CHECKSUM_PARTIAL``.
> +	 */
> +	struct {
> +		u16 csum_start;
> +		u16 csum_offset;
> +	};
> +

CHECKSUM_PARTIAL makes sense on TX, but this RX. I don't see in the above.

> +	/* Checksum, calculated over the whole packet.
> +	 * Available, if ``status & XDP_CHECKSUM_COMPLETE``.
> +	 */
> +	u32 checksum;

imo XDP RX should only support XDP_CHECKSUM_COMPLETE with u32 checksum
or XDP_CHECKSUM_UNNECESSARY.

> +};
> +
> +enum xdp_csum_status {
> +	/* HW had parsed several transport headers and validated their
> +	 * checksums, same as ``CHECKSUM_UNNECESSARY`` in ``sk_buff``.
> +	 * 3 least significant bytes contain number of consecutive checksums,
> +	 * starting with the outermost, reported by hardware as valid.
> +	 * ``sk_buff`` checksum level (``csum_level``) notation is provided
> +	 * for driver developers.
> +	 */
> +	XDP_CHECKSUM_VALID_LVL0		= 1,	/* 1 outermost checksum */
> +	XDP_CHECKSUM_VALID_LVL1		= 2,	/* 2 outermost checksums */
> +	XDP_CHECKSUM_VALID_LVL2		= 3,	/* 3 outermost checksums */
> +	XDP_CHECKSUM_VALID_LVL3		= 4,	/* 4 outermost checksums */
> +	XDP_CHECKSUM_VALID_NUM_MASK	= GENMASK(2, 0),
> +	XDP_CHECKSUM_VALID		= XDP_CHECKSUM_VALID_NUM_MASK,

I don't see what bpf prog suppose to do with these levels.
The driver should pick between 3:
XDP_CHECKSUM_UNNECESSARY, XDP_CHECKSUM_COMPLETE, XDP_CHECKSUM_NONE.

No levels and no anything partial. please.