page_pool: DMA handling and frame recycling via SKBs

During skb_release_data() intercept the packet and if it's a buffer
coming from our page_pool API recycle it back to the pool for further
usage.
To achieve that we introduce a bit in struct sk_buff (pp_recycle:1) and
store the xdp_mem_info in page->private. The SKB bit is needed since
page->private is used by skb_copy_ubufs, so we can't rely solely on
page->private to trigger recycling.

The driver has to take care of the sync operations on it's own
during the buffer recycling since the buffer is never unmapped.

In order to enable recycling the driver must call skb_mark_for_recycle()
to store the information we need for recycling in page->private and
enabling the recycling bit

Storing the information in page->private allows us to recycle both SKBs
and their fragments

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Matteo Croce <mcroce@microsoft.com>

include/linux/skbuff.h

@@ -40,6 +40,9 @@
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 #include <linux/netfilter/nf_conntrack_common.h>
 #endif
+#if IS_BUILTIN(CONFIG_PAGE_POOL)
+#include <net/page_pool.h>
+#endif
 
 /* The interface for checksum offload between the stack and networking drivers
  * is as follows...
@@ -247,6 +250,7 @@ struct napi_struct;
 struct bpf_prog;
 union bpf_attr;
 struct skb_ext;
+struct xdp_mem_info;
 
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 struct nf_bridge_info {
@@ -666,6 +670,8 @@ typedef unsigned char *sk_buff_data_t;
  *	@head_frag: skb was allocated from page fragments,
  *		not allocated by kmalloc() or vmalloc().
  *	@pfmemalloc: skbuff was allocated from PFMEMALLOC reserves
+ *	@pp_recycle: mark the packet for recycling instead of freeing (implies
+ *		page_pool support on driver)
  *	@active_extensions: active extensions (skb_ext_id types)
  *	@ndisc_nodetype: router type (from link layer)
  *	@ooo_okay: allow the mapping of a socket to a queue to be changed
@@ -790,10 +796,12 @@ struct sk_buff {
 				fclone:2,
 				peeked:1,
 				head_frag:1,
-				pfmemalloc:1;
+				pfmemalloc:1,
+				pp_recycle:1; /* page_pool recycle indicator */
 #ifdef CONFIG_SKB_EXTENSIONS
 	__u8			active_extensions;
 #endif
+
 	/* fields enclosed in headers_start/headers_end are copied
 	 * using a single memcpy() in __copy_skb_header()
 	 */
@@ -3081,12 +3089,20 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f)
 /**
  * __skb_frag_unref - release a reference on a paged fragment.
  * @frag: the paged fragment
+ * @recycle: recycle the page if allocated via page_pool
  *
  * Releases a reference on the paged fragment @frag.
+ * or recycles the page via the page_pool API
  */
-static inline void __skb_frag_unref(skb_frag_t *frag)
+static inline void __skb_frag_unref(skb_frag_t *frag, bool recycle)
 {
-	put_page(skb_frag_page(frag));
+	struct page *page = skb_frag_page(frag);
+
+#if IS_BUILTIN(CONFIG_PAGE_POOL)
+	if (recycle && page_pool_return_skb_page(page_address(page)))
+		return;
+#endif
+	put_page(page);
 }
 
 /**
@@ -3098,7 +3114,7 @@ static inline void __skb_frag_unref(skb_frag_t *frag)
  */
 static inline void skb_frag_unref(struct sk_buff *skb, int f)
 {
-	__skb_frag_unref(&skb_shinfo(skb)->frags[f]);
+	__skb_frag_unref(&skb_shinfo(skb)->frags[f], skb->pp_recycle);
 }
 
 /**
@@ -4697,5 +4713,14 @@ static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
 #endif
 }
 
+#if IS_BUILTIN(CONFIG_PAGE_POOL)
+static inline void skb_mark_for_recycle(struct sk_buff *skb, struct page *page,
+					struct xdp_mem_info *mem)
+{
+	skb->pp_recycle = 1;
+	page_pool_store_mem_info(page, mem);
+}
+#endif
+
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */

include/net/page_pool.h

@@ -65,6 +65,8 @@
 #define PP_ALLOC_CACHE_REFILL	64
 #define PP_SIGNATURE		0x20210303
 
+struct xdp_mem_info;
+
 struct pp_alloc_cache {
 	u32 count;
 	void *cache[PP_ALLOC_CACHE_SIZE];
@@ -148,6 +150,8 @@ inline enum dma_data_direction page_pool_get_dma_dir(struct page_pool *pool)
 	return pool->p.dma_dir;
 }
 
+bool page_pool_return_skb_page(void *data);
+
 struct page_pool *page_pool_create(const struct page_pool_params *params);
 
 #ifdef CONFIG_PAGE_POOL
@@ -243,4 +247,13 @@ static inline void page_pool_ring_unlock(struct page_pool *pool)
 		spin_unlock_bh(&pool->ring.producer_lock);
 }
 
+/* Store mem_info on struct page and use it while recycling skb frags */
+static inline
+void page_pool_store_mem_info(struct page *page, struct xdp_mem_info *mem)
+{
+	u32 *xmi = (u32 *)mem;
+
+	set_page_private(page, *xmi);
+}
+
 #endif /* _NET_PAGE_POOL_H */

include/net/xdp.h

@@ -235,6 +235,7 @@ void xdp_return_buff(struct xdp_buff *xdp);
 void xdp_flush_frame_bulk(struct xdp_frame_bulk *bq);
 void xdp_return_frame_bulk(struct xdp_frame *xdpf,
 			   struct xdp_frame_bulk *bq);
+void xdp_return_skb_frame(void *data, struct xdp_mem_info *mem);
 
 /* When sending xdp_frame into the network stack, then there is no
  * return point callback, which is needed to release e.g. DMA-mapping

net/core/page_pool.c

@@ -9,6 +9,7 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/device.h>
+#include <linux/skbuff.h>
 
 #include <net/page_pool.h>
 #include <net/xdp.h>
@@ -17,12 +18,19 @@
 #include <linux/dma-mapping.h>
 #include <linux/page-flags.h>
 #include <linux/mm.h> /* for __put_page() */
+#include <net/xdp.h>
 
 #include <trace/events/page_pool.h>
 
 #define DEFER_TIME (msecs_to_jiffies(1000))
 #define DEFER_WARN_INTERVAL (60 * HZ)
 
+/* Used to store/retrieve hi/lo bytes from xdp_mem_info to page->private */
+union page_pool_xmi {
+	u32 raw;
+	struct xdp_mem_info mem_info;
+};
+
 static int page_pool_init(struct page_pool *pool,
 			  const struct page_pool_params *params)
 {
@@ -587,3 +595,38 @@ void page_pool_update_nid(struct page_pool *pool, int new_nid)
 	}
 }
 EXPORT_SYMBOL(page_pool_update_nid);
+
+bool page_pool_return_skb_page(void *data)
+{
+	struct xdp_mem_info mem_info;
+	union page_pool_xmi info;
+	struct page *page;
+
+	page = virt_to_head_page(data);
+	if (unlikely(page->signature != PP_SIGNATURE))
+		return false;
+
+	info.raw = page_private(page);
+	mem_info = info.mem_info;
+
+	/* If a buffer is marked for recycle and does not belong to
+	 * MEM_TYPE_PAGE_POOL, the buffers will be eventually freed from the
+	 * network stack and kfree_skb, but the DMA region will *not* be
+	 * correctly unmapped. WARN here for the recycling misusage
+	 */
+	if (unlikely(mem_info.type != MEM_TYPE_PAGE_POOL)) {
+		WARN_ONCE(true, "Tried to recycle non MEM_TYPE_PAGE_POOL");
+		return false;
+	}
+
+	/* Driver set this to memory recycling info. Reset it on recycle
+	 * This will *not* work for NIC using a split-page memory model.
+	 * The page will be returned to the pool here regardless of the
+	 * 'flipped' fragment being in use or not
+	 */
+	set_page_private(page, 0);
+	xdp_return_skb_frame(data, &mem_info);
+
+	return true;
+}
+EXPORT_SYMBOL(page_pool_return_skb_page);

net/core/skbuff.c

@@ -69,6 +69,9 @@
 #include <net/xfrm.h>
 #include <net/mpls.h>
 #include <net/mptcp.h>
+#if IS_BUILTIN(CONFIG_PAGE_POOL)
+#include <net/page_pool.h>
+#endif
 
 #include <linux/uaccess.h>
 #include <trace/events/skb.h>
@@ -644,6 +647,11 @@ static void skb_free_head(struct sk_buff *skb)
 {
 	unsigned char *head = skb->head;
 
+#if IS_BUILTIN(CONFIG_PAGE_POOL)
+	if (skb->pp_recycle && page_pool_return_skb_page(head))
+		return;
+#endif
+
 	if (skb->head_frag)
 		skb_free_frag(head);
 	else
@@ -663,7 +671,7 @@ static void skb_release_data(struct sk_buff *skb)
 	skb_zcopy_clear(skb, true);
 
 	for (i = 0; i < shinfo->nr_frags; i++)
-		__skb_frag_unref(&shinfo->frags[i]);
+		__skb_frag_unref(&shinfo->frags[i], skb->pp_recycle);
 
 	if (shinfo->frag_list)
 		kfree_skb_list(shinfo->frag_list);
@@ -1045,6 +1053,7 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
 	n->nohdr = 0;
 	n->peeked = 0;
 	C(pfmemalloc);
+	C(pp_recycle);
 	n->destructor = NULL;
 	C(tail);
 	C(end);
@@ -3453,7 +3462,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
 		fragto = &skb_shinfo(tgt)->frags[merge];
 
 		skb_frag_size_add(fragto, skb_frag_size(fragfrom));
-		__skb_frag_unref(fragfrom);
+		__skb_frag_unref(fragfrom, skb->pp_recycle);
 	}
 
 	/* Reposition in the original skb */
@@ -5234,6 +5243,13 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
 	if (skb_cloned(to))
 		return false;
 
+	/* We can't coalesce skb that are allocated from slab and page_pool
+	 * The recycle mark is on the skb, so that might end up trying to
+	 * recycle slab allocated skb->head
+	 */
+	if (to->pp_recycle != from->pp_recycle)
+		return false;
+
 	if (len <= skb_tailroom(to)) {
 		if (len)
 			BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));

net/core/xdp.c

@@ -372,6 +372,12 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
 	}
 }
 
+void xdp_return_skb_frame(void *data, struct xdp_mem_info *mem)
+{
+	__xdp_return(data, mem, false, 0);
+}
+EXPORT_SYMBOL_GPL(xdp_return_skb_frame);
+
 void xdp_return_frame(struct xdp_frame *xdpf)
 {
 	__xdp_return(xdpf->data, &xdpf->mem, false, NULL);