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From: Martin KaFai Lau <martin.lau@linux.dev>
To: Stanislav Fomichev <sdf@google.com>
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
	song@kernel.org, yhs@fb.com, john.fastabend@gmail.com,
	kpsingh@kernel.org, haoluo@google.com, jolsa@kernel.org,
	David Ahern <dsahern@gmail.com>, Jakub Kicinski <kuba@kernel.org>,
	Willem de Bruijn <willemb@google.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Anatoly Burakov <anatoly.burakov@intel.com>,
	Alexander Lobakin <alexandr.lobakin@intel.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>,
	Maryam Tahhan <mtahhan@redhat.com>,
	xdp-hints@xdp-project.net, netdev@vger.kernel.org,
	bpf@vger.kernel.org
Subject: [xdp-hints] Re: [RFC bpf-next v2 06/14] xdp: Carry over xdp metadata into skb context
Date: Mon, 7 Nov 2022 14:01:53 -0800	[thread overview]
Message-ID: <187e89c3-d7de-7bec-c72e-d9d6eb5bcca0@linux.dev> (raw)
In-Reply-To: <20221104032532.1615099-7-sdf@google.com>

On 11/3/22 8:25 PM, Stanislav Fomichev wrote:
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 59c9fd55699d..dba857f212d7 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -4217,9 +4217,13 @@ static inline bool skb_metadata_differs(const struct sk_buff *skb_a,
>   	       true : __skb_metadata_differs(skb_a, skb_b, len_a);
>   }
>   
> +void skb_metadata_import_from_xdp(struct sk_buff *skb, size_t len);
> +
>   static inline void skb_metadata_set(struct sk_buff *skb, u8 meta_len)
>   {
>   	skb_shinfo(skb)->meta_len = meta_len;
> +	if (meta_len)
> +		skb_metadata_import_from_xdp(skb, meta_len);
>   }
>
[ ... ]

> +struct xdp_to_skb_metadata {
> +	u32 magic; /* xdp_metadata_magic */
> +	u64 rx_timestamp;
> +} __randomize_layout;
> +
> +struct bpf_patch;
> +

[ ... ]

> +void skb_metadata_import_from_xdp(struct sk_buff *skb, size_t len)
> +{
> +	struct xdp_to_skb_metadata *meta = (void *)(skb_mac_header(skb) - len);
> +
> +	/* Optional SKB info, currently missing:
> +	 * - HW checksum info		(skb->ip_summed)
> +	 * - HW RX hash			(skb_set_hash)
> +	 * - RX ring dev queue index	(skb_record_rx_queue)
> +	 */
> +
> +	if (len != sizeof(struct xdp_to_skb_metadata))
> +		return;
> +
> +	if (meta->magic != xdp_metadata_magic)
> +		return;
> +
> +	if (meta->rx_timestamp) {
> +		*skb_hwtstamps(skb) = (struct skb_shared_hwtstamps){
> +			.hwtstamp = ns_to_ktime(meta->rx_timestamp),
> +		};
> +	}
> +}

Considering the metadata will affect the gro, should the meta be cleared after 
importing to the skb?

[ ... ]

> +/* Since we're not actually doing a call but instead rewriting
> + * in place, we can only afford to use R0-R5 scratch registers.
> + *
> + * We reserve R1 for bpf_xdp_metadata_export_to_skb and let individual
> + * metadata kfuncs use only R0,R4-R5.
> + *
> + * The above also means we _cannot_ easily call any other helper/kfunc
> + * because there is no place for us to preserve our R1 argument;
> + * existing R6-R9 belong to the callee.
> + */
> +void xdp_metadata_export_to_skb(const struct bpf_prog *prog, struct bpf_patch *patch)
> +{
> +	u32 func_id;
> +
> +	/*
> +	 * The code below generates the following:
> +	 *
> +	 * void bpf_xdp_metadata_export_to_skb(struct xdp_md *ctx)
> +	 * {
> +	 *	struct xdp_to_skb_metadata *meta;
> +	 *	int ret;
> +	 *
> +	 *	ret = bpf_xdp_adjust_meta(ctx, -sizeof(*meta));
> +	 *	if (!ret)
> +	 *		return;
> +	 *
> +	 *	meta = ctx->data_meta;
> +	 *	meta->magic = xdp_metadata_magic;
> +	 *	meta->rx_timestamp = bpf_xdp_metadata_rx_timestamp(ctx);
> +	 * }
> +	 *
> +	 */
> +
> +	bpf_patch_append(patch,
> +		/* r2 = ((struct xdp_buff *)r1)->data_meta; */
> +		BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1,
> +			    offsetof(struct xdp_buff, data_meta)),
> +		/* r3 = ((struct xdp_buff *)r1)->data; */
> +		BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_1,
> +			    offsetof(struct xdp_buff, data)),
> +		/* if (data_meta != data) return;
> +		 *
> +		 *	data_meta > data: xdp_data_meta_unsupported()
> +		 *	data_meta < data: already used, no need to touch
> +		 */
> +		BPF_JMP_REG(BPF_JNE, BPF_REG_2, BPF_REG_3, S16_MAX),
> +
> +		/* r2 -= sizeof(struct xdp_to_skb_metadata); */
> +		BPF_ALU64_IMM(BPF_SUB, BPF_REG_2,
> +			      sizeof(struct xdp_to_skb_metadata)),
> +		/* r3 = ((struct xdp_buff *)r1)->data_hard_start; */
> +		BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_1,
> +			    offsetof(struct xdp_buff, data_hard_start)),
> +		/* r3 += sizeof(struct xdp_frame) */
> +		BPF_ALU64_IMM(BPF_ADD, BPF_REG_3,
> +			      sizeof(struct xdp_frame)),
> +		/* if (data-sizeof(struct xdp_to_skb_metadata) < data_hard_start+sizeof(struct xdp_frame)) return; */
> +		BPF_JMP_REG(BPF_JLT, BPF_REG_2, BPF_REG_3, S16_MAX),
> +
> +		/* ((struct xdp_buff *)r1)->data_meta = r2; */
> +		BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_2,
> +			    offsetof(struct xdp_buff, data_meta)),
> +
> +		/* *((struct xdp_to_skb_metadata *)r2)->magic = xdp_metadata_magic; */
> +		BPF_ST_MEM(BPF_W, BPF_REG_2,
> +			   offsetof(struct xdp_to_skb_metadata, magic),
> +			   xdp_metadata_magic),
> +	);
> +
> +	/*	r0 = bpf_xdp_metadata_rx_timestamp(ctx); */
> +	func_id = xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP);
> +	prog->aux->xdp_kfunc_ndo->ndo_unroll_kfunc(prog, func_id, patch);
> +
> +	bpf_patch_append(patch,
> +		/* r2 = ((struct xdp_buff *)r1)->data_meta; */
> +		BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1,
> +			    offsetof(struct xdp_buff, data_meta)),
> +		/* *((struct xdp_to_skb_metadata *)r2)->rx_timestamp = r0; */
> +		BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_0,
> +			    offsetof(struct xdp_to_skb_metadata, rx_timestamp)),

Can the xdp prog still change the metadata through xdp->data_meta? tbh, I am not 
sure it is solid enough by asking the xdp prog not to use the same random number 
in its own metadata + not to change the metadata through xdp->data_meta after 
calling bpf_xdp_metadata_export_to_skb().

Does xdp_to_skb_metadata have a use case for XDP_PASS (like patch 7) or the 
xdp_to_skb_metadata can be limited to XDP_REDIRECT only?


> +	);
> +
> +	bpf_patch_resolve_jmp(patch);
> +}
> +
>   static int __init xdp_metadata_init(void)
>   {
> +	xdp_metadata_magic = get_random_u32() | 1;
>   	return register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &xdp_metadata_kfunc_set);
>   }
>   late_initcall(xdp_metadata_init);

  reply	other threads:[~2022-11-07 22:02 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-04  3:25 [xdp-hints] [RFC bpf-next v2 00/14] xdp: hints via kfuncs Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 01/14] bpf: Introduce bpf_patch Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 02/14] bpf: Support inlined/unrolled kfuncs for xdp metadata Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 03/14] veth: Introduce veth_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 04/14] veth: Support rx timestamp metadata for xdp Stanislav Fomichev
2022-11-09 11:21   ` [xdp-hints] " Toke Høiland-Jørgensen
2022-11-09 21:34     ` Stanislav Fomichev
2022-11-10  0:25   ` John Fastabend
2022-11-10  1:02     ` Stanislav Fomichev
2022-11-10  1:35       ` John Fastabend
2022-11-10  6:44         ` Stanislav Fomichev
2022-11-10 17:39           ` John Fastabend
2022-11-10 18:52             ` Stanislav Fomichev
2022-11-11 10:41             ` Jesper Dangaard Brouer
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 05/14] selftests/bpf: Verify xdp_metadata xdp->af_xdp path Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 06/14] xdp: Carry over xdp metadata into skb context Stanislav Fomichev
2022-11-07 22:01   ` Martin KaFai Lau [this message]
2022-11-08 21:54     ` [xdp-hints] " Stanislav Fomichev
2022-11-09  3:07       ` Martin KaFai Lau
2022-11-09  4:19         ` Martin KaFai Lau
2022-11-09 11:10           ` Toke Høiland-Jørgensen
2022-11-09 18:22             ` Martin KaFai Lau
2022-11-09 21:33               ` Stanislav Fomichev
2022-11-10  0:13                 ` Martin KaFai Lau
2022-11-10  1:02                   ` Stanislav Fomichev
2022-11-10 14:26                     ` Toke Høiland-Jørgensen
2022-11-10 18:52                       ` Stanislav Fomichev
2022-11-10 23:14                         ` Toke Høiland-Jørgensen
2022-11-10 23:52                           ` Stanislav Fomichev
2022-11-11  0:10                             ` Toke Høiland-Jørgensen
2022-11-11  0:45                               ` Martin KaFai Lau
2022-11-11  9:37                                 ` Toke Høiland-Jørgensen
2022-11-11  0:33                             ` Martin KaFai Lau
2022-11-11  0:57                               ` Stanislav Fomichev
2022-11-11  1:26                                 ` Martin KaFai Lau
2022-11-11  9:41                                   ` Toke Høiland-Jørgensen
2022-11-10 23:58                         ` Martin KaFai Lau
2022-11-11  0:20                           ` Stanislav Fomichev
2022-11-10 14:19               ` Toke Høiland-Jørgensen
2022-11-10 19:04                 ` Martin KaFai Lau
2022-11-10 23:29                   ` Toke Høiland-Jørgensen
2022-11-11  1:39                     ` Martin KaFai Lau
2022-11-11  9:44                       ` Toke Høiland-Jørgensen
2022-11-10  1:26             ` John Fastabend
2022-11-10 14:32               ` Toke Høiland-Jørgensen
2022-11-10 17:30                 ` John Fastabend
2022-11-10 22:49                   ` Toke Høiland-Jørgensen
2022-11-10  1:09   ` John Fastabend
2022-11-10  6:44     ` Stanislav Fomichev
2022-11-10 21:21       ` David Ahern
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 07/14] selftests/bpf: Verify xdp_metadata xdp->skb path Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 08/14] bpf: Helper to simplify calling kernel routines from unrolled kfuncs Stanislav Fomichev
2022-11-05  0:40   ` [xdp-hints] " Alexei Starovoitov
2022-11-05  2:18     ` Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 09/14] ice: Introduce ice_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 10/14] ice: Support rx timestamp metadata for xdp Stanislav Fomichev
2022-11-04 14:35   ` [xdp-hints] " Alexander Lobakin
2022-11-04 18:21     ` Stanislav Fomichev
2022-11-07 17:11       ` Alexander Lobakin
2022-11-07 19:10         ` Stanislav Fomichev
2022-12-15 11:54   ` Larysa Zaremba
2022-12-15 14:29     ` Toke Høiland-Jørgensen
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 11/14] mlx4: Introduce mlx4_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 12/14] mxl4: Support rx timestamp metadata for xdp Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 13/14] bnxt: Introduce bnxt_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-11-04  3:25 ` [xdp-hints] [RFC bpf-next v2 14/14] bnxt: Support rx timestamp metadata for xdp Stanislav Fomichev

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