[PATCH v12 bpf-next 05/18] net: xdp: add xdp_update_skb_shared_info utility routine

[PATCH v12 bpf-next 05/18] net: xdp: add xdp_update_skb_shared_info utility routine

[Lorenzo Bianconi]

Introduce xdp_update_skb_shared_info routine to update frags array
metadata in skb_shared_info data structure converting to a skb from
a xdp_buff or xdp_frame.
According to the current skb_shared_info architecture in
xdp_frame/xdp_buff and to the xdp multi-buff support, there is
no need to run skb_add_rx_frag() and reset frags array converting the buffer
to a skb since the frag array will be in the same position for xdp_buff/xdp_frame
and for the skb, we just need to update memory metadata.
Introduce XDP_FLAGS_PF_MEMALLOC flag in xdp_buff_flags in order to mark
the xdp_buff or xdp_frame as under memory-pressure if pages of the frags array
are under memory pressure. Doing so we can avoid looping over all fragments in
xdp_update_skb_shared_info routine. The driver is expected to set the
flag constructing the xdp_buffer using xdp_buff_set_frag_pfmemalloc
utility routine.
Rely on xdp_update_skb_shared_info in __xdp_build_skb_from_frame routine
converting the multi-buff xdp_frame to a skb after performing a XDP_REDIRECT.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 include/net/xdp.h | 33 ++++++++++++++++++++++++++++++++-
 net/core/xdp.c    | 17 +++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index ed5ea784fd45..53cccdc9528c 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -67,7 +67,10 @@ struct xdp_txq_info {
 };
 
 enum xdp_buff_flags {
-	XDP_FLAGS_MULTI_BUFF	= BIT(0), /* non-linear xdp buff */
+	XDP_FLAGS_MULTI_BUFF		= BIT(0), /* non-linear xdp buff */
+	XDP_FLAGS_FRAGS_PF_MEMALLOC	= BIT(1), /* xdp multi-buff paged memory
+						   * is under pressure
+						   */
 };
 
 struct xdp_buff {
@@ -96,6 +99,16 @@ static __always_inline void xdp_buff_clear_mb(struct xdp_buff *xdp)
 	xdp->flags &= ~XDP_FLAGS_MULTI_BUFF;
 }
 
+static __always_inline bool xdp_buff_is_frag_pfmemalloc(struct xdp_buff *xdp)
+{
+	return !!(xdp->flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
+}
+
+static __always_inline void xdp_buff_set_frag_pfmemalloc(struct xdp_buff *xdp)
+{
+	xdp->flags |= XDP_FLAGS_FRAGS_PF_MEMALLOC;
+}
+
 static __always_inline void
 xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
 {
@@ -151,6 +164,11 @@ static __always_inline bool xdp_frame_is_mb(struct xdp_frame *frame)
 	return !!(frame->flags & XDP_FLAGS_MULTI_BUFF);
 }
 
+static __always_inline bool xdp_frame_is_frag_pfmemalloc(struct xdp_frame *frame)
+{
+	return !!(frame->flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
+}
+
 #define XDP_BULK_QUEUE_SIZE	16
 struct xdp_frame_bulk {
 	int count;
@@ -186,6 +204,19 @@ static inline void xdp_scrub_frame(struct xdp_frame *frame)
 	frame->dev_rx = NULL;
 }
 
+static inline void
+xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
+			   unsigned int size, unsigned int truesize,
+			   bool pfmemalloc)
+{
+	skb_shinfo(skb)->nr_frags = nr_frags;
+
+	skb->len += size;
+	skb->data_len += size;
+	skb->truesize += truesize;
+	skb->pfmemalloc |= pfmemalloc;
+}
+
 /* Avoids inlining WARN macro in fast-path */
 void xdp_warn(const char *msg, const char *func, const int line);
 #define XDP_WARN(msg) xdp_warn(msg, __func__, __LINE__)
diff --git a/net/core/xdp.c b/net/core/xdp.c
index cc92ccb38432..504be3ce3ca9 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -531,8 +531,20 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
 					   struct sk_buff *skb,
 					   struct net_device *dev)
 {
+	unsigned int frag_size, frag_tsize;
 	unsigned int headroom, frame_size;
 	void *hard_start;
+	u8 nr_frags;
+
+	/* xdp multi-buff frame */
+	if (unlikely(xdp_frame_is_mb(xdpf))) {
+		struct skb_shared_info *sinfo;
+
+		sinfo = xdp_get_shared_info_from_frame(xdpf);
+		frag_tsize = sinfo->xdp_frags_tsize;
+		frag_size = sinfo->xdp_frags_size;
+		nr_frags = sinfo->nr_frags;
+	}
 
 	/* Part of headroom was reserved to xdpf */
 	headroom = sizeof(*xdpf) + xdpf->headroom;
@@ -552,6 +564,11 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
 	if (xdpf->metasize)
 		skb_metadata_set(skb, xdpf->metasize);
 
+	if (unlikely(xdp_frame_is_mb(xdpf)))
+		xdp_update_skb_shared_info(skb, nr_frags,
+					   frag_size, frag_tsize,
+					   xdp_frame_is_frag_pfmemalloc(xdpf));
+
 	/* Essential SKB info: protocol and skb->dev */
 	skb->protocol = eth_type_trans(skb, dev);
 
-- 
2.31.1

Re: [PATCH v12 bpf-next 05/18] net: xdp: add xdp_update_skb_shared_info utility routine

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 6384 bytes --]

CC: kbuild-all(a)lists.01.org
In-Reply-To: <3d98cda6f49ef9ff34d2aec3d00924592b4739e3.1629473233.git.lorenzo@kernel.org>
References: <3d98cda6f49ef9ff34d2aec3d00924592b4739e3.1629473233.git.lorenzo@kernel.org>
TO: Lorenzo Bianconi <lorenzo@kernel.org>
TO: bpf(a)vger.kernel.org
TO: netdev(a)vger.kernel.org
CC: lorenzo.bianconi(a)redhat.com
CC: davem(a)davemloft.net
CC: kuba(a)kernel.org
CC: ast(a)kernel.org
CC: daniel(a)iogearbox.net
CC: shayagr(a)amazon.com
CC: john.fastabend(a)gmail.com
CC: dsahern(a)kernel.org

Hi Lorenzo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/0day-ci/linux/commits/Lorenzo-Bianconi/mvneta-introduce-XDP-multi-buffer-support/20210820-234736
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
:::::: branch date: 9 days ago
:::::: commit date: 9 days ago
config: i386-randconfig-m021-20210829 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

smatch warnings:
net/core/xdp.c:568 __xdp_build_skb_from_frame() error: uninitialized symbol 'nr_frags'.
net/core/xdp.c:569 __xdp_build_skb_from_frame() error: uninitialized symbol 'frag_size'.
net/core/xdp.c:569 __xdp_build_skb_from_frame() error: uninitialized symbol 'frag_tsize'.

vim +/nr_frags +568 net/core/xdp.c

65e6dcf73398dd Lorenzo Bianconi 2021-01-29  529  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  530  struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  531  					   struct sk_buff *skb,
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  532  					   struct net_device *dev)
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  533  {
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  534  	unsigned int frag_size, frag_tsize;
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  535  	unsigned int headroom, frame_size;
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  536  	void *hard_start;
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  537  	u8 nr_frags;
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  538  
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  539  	/* xdp multi-buff frame */
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  540  	if (unlikely(xdp_frame_is_mb(xdpf))) {
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  541  		struct skb_shared_info *sinfo;
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  542  
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  543  		sinfo = xdp_get_shared_info_from_frame(xdpf);
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  544  		frag_tsize = sinfo->xdp_frags_tsize;
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  545  		frag_size = sinfo->xdp_frags_size;
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  546  		nr_frags = sinfo->nr_frags;
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  547  	}
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  548  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  549  	/* Part of headroom was reserved to xdpf */
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  550  	headroom = sizeof(*xdpf) + xdpf->headroom;
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  551  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  552  	/* Memory size backing xdp_frame data already have reserved
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  553  	 * room for build_skb to place skb_shared_info in tailroom.
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  554  	 */
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  555  	frame_size = xdpf->frame_sz;
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  556  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  557  	hard_start = xdpf->data - headroom;
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  558  	skb = build_skb_around(skb, hard_start, frame_size);
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  559  	if (unlikely(!skb))
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  560  		return NULL;
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  561  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  562  	skb_reserve(skb, headroom);
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  563  	__skb_put(skb, xdpf->len);
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  564  	if (xdpf->metasize)
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  565  		skb_metadata_set(skb, xdpf->metasize);
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  566  
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  567  	if (unlikely(xdp_frame_is_mb(xdpf)))
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20 @568  		xdp_update_skb_shared_info(skb, nr_frags,
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20 @569  					   frag_size, frag_tsize,
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  570  					   xdp_frame_is_frag_pfmemalloc(xdpf));
2f8c6ede2e6e56 Lorenzo Bianconi 2021-08-20  571  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  572  	/* Essential SKB info: protocol and skb->dev */
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  573  	skb->protocol = eth_type_trans(skb, dev);
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  574  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  575  	/* Optional SKB info, currently missing:
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  576  	 * - HW checksum info		(skb->ip_summed)
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  577  	 * - HW RX hash			(skb_set_hash)
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  578  	 * - RX ring dev queue index	(skb_record_rx_queue)
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  579  	 */
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  580  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  581  	/* Until page_pool get SKB return path, release DMA here */
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  582  	xdp_release_frame(xdpf);
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  583  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  584  	/* Allow SKB to reuse area used by xdp_frame */
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  585  	xdp_scrub_frame(xdpf);
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  586  
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  587  	return skb;
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  588  }
97a0e1ea7b41c2 Lorenzo Bianconi 2021-01-12  589  EXPORT_SYMBOL_GPL(__xdp_build_skb_from_frame);
89f479f0eccfc8 Lorenzo Bianconi 2021-01-12  590  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

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RE: [PATCH v12 bpf-next 05/18] net: xdp: add xdp_update_skb_shared_info utility routine

[John Fastabend]

Lorenzo Bianconi wrote:
> Introduce xdp_update_skb_shared_info routine to update frags array
> metadata in skb_shared_info data structure converting to a skb from
> a xdp_buff or xdp_frame.
> According to the current skb_shared_info architecture in
> xdp_frame/xdp_buff and to the xdp multi-buff support, there is
> no need to run skb_add_rx_frag() and reset frags array converting the buffer
> to a skb since the frag array will be in the same position for xdp_buff/xdp_frame
> and for the skb, we just need to update memory metadata.
> Introduce XDP_FLAGS_PF_MEMALLOC flag in xdp_buff_flags in order to mark
> the xdp_buff or xdp_frame as under memory-pressure if pages of the frags array
> are under memory pressure. Doing so we can avoid looping over all fragments in
> xdp_update_skb_shared_info routine. The driver is expected to set the
> flag constructing the xdp_buffer using xdp_buff_set_frag_pfmemalloc
> utility routine.
> Rely on xdp_update_skb_shared_info in __xdp_build_skb_from_frame routine
> converting the multi-buff xdp_frame to a skb after performing a XDP_REDIRECT.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>

Acked-by: John Fastabend <john.fastabend@gmail.com>