[RFC PATCH v2 07/11] net: support non paged skb frags

[Mina Almasry <almasrymina@xxxxxxxxxx>]

Make skb_frag_page() fail in the case where the frag is not backed
by a page, and fix its relevent callers to handle this case.

Correctly handle skb_frag refcounting in the page_pool_iovs case.

Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>
---
 include/linux/skbuff.h | 40 +++++++++++++++++++++++++++++++++-------
 net/core/gro.c         |  2 +-
 net/core/skbuff.c      |  3 +++
 net/ipv4/tcp.c         | 10 +++++++++-
 4 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index faaba050f843..5520587050c4 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3389,15 +3389,38 @@ static inline void skb_frag_off_copy(skb_frag_t *fragto,
 	fragto->bv_offset = fragfrom->bv_offset;
 }
 
+/* Returns true if the skb_frag contains a page_pool_iov. */
+static inline bool skb_frag_is_page_pool_iov(const skb_frag_t *frag)
+{
+	return page_is_page_pool_iov(frag->bv_page);
+}
+
 /**
  * skb_frag_page - retrieve the page referred to by a paged fragment
  * @frag: the paged fragment
  *
- * Returns the &struct page associated with @frag.
+ * Returns the &struct page associated with @frag. Returns NULL if this frag
+ * has no associated page.
  */
 static inline struct page *skb_frag_page(const skb_frag_t *frag)
 {
-	return frag->bv_page;
+	if (!page_is_page_pool_iov(frag->bv_page))
+		return frag->bv_page;
+
+	return NULL;
+}
+
+/**
+ * skb_frag_page_pool_iov - retrieve the page_pool_iov referred to by fragment
+ * @frag: the fragment
+ *
+ * Returns the &struct page_pool_iov associated with @frag. Returns NULL if this
+ * frag has no associated page_pool_iov.
+ */
+static inline struct page_pool_iov *
+skb_frag_page_pool_iov(const skb_frag_t *frag)
+{
+	return page_to_page_pool_iov(frag->bv_page);
 }
 
 /**
@@ -3408,7 +3431,7 @@ static inline struct page *skb_frag_page(const skb_frag_t *frag)
  */
 static inline void __skb_frag_ref(skb_frag_t *frag)
 {
-	get_page(skb_frag_page(frag));
+	page_pool_page_get_many(frag->bv_page, 1);
 }
 
 /**
@@ -3426,13 +3449,13 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f)
 static inline void
 napi_frag_unref(skb_frag_t *frag, bool recycle, bool napi_safe)
 {
-	struct page *page = skb_frag_page(frag);
-
 #ifdef CONFIG_PAGE_POOL
-	if (recycle && page_pool_return_skb_page(page, napi_safe))
+	if (recycle && page_pool_return_skb_page(frag->bv_page, napi_safe))
 		return;
+	page_pool_page_put_many(frag->bv_page, 1);
+#else
+	put_page(skb_frag_page(frag));
 #endif
-	put_page(page);
 }
 
 /**
@@ -3472,6 +3495,9 @@ static inline void skb_frag_unref(struct sk_buff *skb, int f)
  */
 static inline void *skb_frag_address(const skb_frag_t *frag)
 {
+	if (!skb_frag_page(frag))
+		return NULL;
+
 	return page_address(skb_frag_page(frag)) + skb_frag_off(frag);
 }
 
diff --git a/net/core/gro.c b/net/core/gro.c
index 0759277dc14e..42d7f6755f32 100644
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -376,7 +376,7 @@ static inline void skb_gro_reset_offset(struct sk_buff *skb, u32 nhoff)
 	NAPI_GRO_CB(skb)->frag0 = NULL;
 	NAPI_GRO_CB(skb)->frag0_len = 0;
 
-	if (!skb_headlen(skb) && pinfo->nr_frags &&
+	if (!skb_headlen(skb) && pinfo->nr_frags && skb_frag_page(frag0) &&
 	    !PageHighMem(skb_frag_page(frag0)) &&
 	    (!NET_IP_ALIGN || !((skb_frag_off(frag0) + nhoff) & 3))) {
 		NAPI_GRO_CB(skb)->frag0 = skb_frag_address(frag0);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a298992060e6..ac79881a2630 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2939,6 +2939,9 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
 	for (seg = 0; seg < skb_shinfo(skb)->nr_frags; seg++) {
 		const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];
 
+		if (WARN_ON_ONCE(!skb_frag_page(f)))
+			return false;
+
 		if (__splice_segment(skb_frag_page(f),
 				     skb_frag_off(f), skb_frag_size(f),
 				     offset, len, spd, false, sk, pipe))
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 88f4ebab12ac..7893df0e22ee 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2160,6 +2160,9 @@ static int tcp_zerocopy_receive(struct sock *sk,
 			break;
 		}
 		page = skb_frag_page(frags);
+		if (WARN_ON_ONCE(!page))
+			break;
+
 		prefetchw(page);
 		pages[pages_to_map++] = page;
 		length += PAGE_SIZE;
@@ -4415,7 +4418,12 @@ int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *hp,
 	for (i = 0; i < shi->nr_frags; ++i) {
 		const skb_frag_t *f = &shi->frags[i];
 		unsigned int offset = skb_frag_off(f);
-		struct page *page = skb_frag_page(f) + (offset >> PAGE_SHIFT);
+		struct page *page = skb_frag_page(f);
+
+		if (WARN_ON_ONCE(!page))
+			return 1;
+
+		page += offset >> PAGE_SHIFT;
 
 		sg_set_page(&sg, page, skb_frag_size(f),
 			    offset_in_page(offset));
-- 
2.41.0.640.ga95def55d0-goog