get_page() in __zerocopy_sg_from_bvec() and matching put_page()s are
expensive. However, we can avoid it if the caller can guarantee that
pages stay alive until the corresponding ubuf_info is not released.
In particular, it targets io_uring with fixed buffers following the
described contract.
Assuming that nobody yet uses bvec together with zerocopy, make all
calls with bvec iterators follow this model.
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
include/linux/skbuff.h | 12 ++++++++++--
net/core/datagram.c | 9 +++++++--
net/core/skbuff.c | 14 +++++++++++++-
3 files changed, 30 insertions(+), 5 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index b80944a9ce8f..f6a6fd67e1ea 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -461,11 +461,16 @@ enum {
SKBFL_PURE_ZEROCOPY = BIT(2),
SKBFL_DONT_ORPHAN = BIT(3),
+
+ /* page references are managed by the ubuf_info, so it's safe to
+ * use frags only up until ubuf_info is released
+ */
+ SKBFL_MANAGED_FRAGS = BIT(4),
};
#define SKBFL_ZEROCOPY_FRAG (SKBFL_ZEROCOPY_ENABLE | SKBFL_SHARED_FRAG)
#define SKBFL_ALL_ZEROCOPY (SKBFL_ZEROCOPY_FRAG | SKBFL_PURE_ZEROCOPY | \
- SKBFL_DONT_ORPHAN)
+ SKBFL_DONT_ORPHAN | SKBFL_MANAGED_FRAGS)
/*
* The callback notifies userspace to release buffers when skb DMA is done in
@@ -3155,7 +3160,10 @@ static inline void __skb_frag_unref(skb_frag_t *frag, bool recycle)
*/
static inline void skb_frag_unref(struct sk_buff *skb, int f)
{
- __skb_frag_unref(&skb_shinfo(skb)->frags[f], skb->pp_recycle);
+ struct skb_shared_info *shinfo = skb_shinfo(skb);
+
+ if (!(shinfo->flags & SKBFL_MANAGED_FRAGS))
+ __skb_frag_unref(&shinfo->frags[f], skb->pp_recycle);
}
/**
diff --git a/net/core/datagram.c b/net/core/datagram.c
index cb1e34fbcd44..46526af40552 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -638,7 +638,6 @@ static int __zerocopy_sg_from_bvec(struct sock *sk, struct sk_buff *skb,
v = mp_bvec_iter_bvec(from->bvec, bi);
copied += v.bv_len;
truesize += PAGE_ALIGN(v.bv_len + v.bv_offset);
- get_page(v.bv_page);
skb_fill_page_desc(skb, frag++, v.bv_page, v.bv_offset, v.bv_len);
bvec_iter_advance_single(from->bvec, &bi, v.bv_len);
}
@@ -667,9 +666,15 @@ int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
struct iov_iter *from, size_t length)
{
int frag = skb_shinfo(skb)->nr_frags;
+ bool managed = skb_shinfo(skb)->flags & SKBFL_MANAGED_FRAGS;
- if (iov_iter_is_bvec(from))
+ if (iov_iter_is_bvec(from) && (managed || frag == 0)) {
+ skb_shinfo(skb)->flags |= SKBFL_MANAGED_FRAGS;
return __zerocopy_sg_from_bvec(sk, skb, from, length);
+ }
+
+ if (managed)
+ return -EFAULT;
while (length && iov_iter_count(from)) {
struct page *pages[MAX_SKB_FRAGS];
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b23db60ea6f9..10cdcb99d34b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -666,11 +666,18 @@ static void skb_release_data(struct sk_buff *skb)
&shinfo->dataref))
goto exit;
- skb_zcopy_clear(skb, true);
+ if (skb_zcopy(skb)) {
+ bool skip_unref = shinfo->flags & SKBFL_MANAGED_FRAGS;
+
+ skb_zcopy_clear(skb, true);
+ if (skip_unref)
+ goto free_head;
+ }
for (i = 0; i < shinfo->nr_frags; i++)
__skb_frag_unref(&shinfo->frags[i], skb->pp_recycle);
+free_head:
if (shinfo->frag_list)
kfree_skb_list(shinfo->frag_list);
@@ -1597,6 +1604,7 @@ struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
BUG_ON(skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len));
skb_copy_header(n, skb);
+ skb_shinfo(n)->flags &= ~SKBFL_MANAGED_FRAGS;
return n;
}
EXPORT_SYMBOL(skb_copy);
@@ -1653,6 +1661,7 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
skb_frag_ref(skb, i);
}
skb_shinfo(n)->nr_frags = i;
+ skb_shinfo(n)->flags &= ~SKBFL_MANAGED_FRAGS;
}
if (skb_has_frag_list(skb)) {
@@ -1725,6 +1734,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
refcount_inc(&skb_uarg(skb)->refcnt);
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
skb_frag_ref(skb, i);
+ skb_shinfo(skb)->flags &= ~SKBFL_MANAGED_FRAGS;
if (skb_has_frag_list(skb))
skb_clone_fraglist(skb);
@@ -3788,6 +3798,8 @@ int skb_append_pagefrags(struct sk_buff *skb, struct page *page,
if (skb_can_coalesce(skb, i, page, offset)) {
skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], size);
} else if (i < MAX_SKB_FRAGS) {
+ if (skb_shinfo(skb)->flags & SKBFL_MANAGED_FRAGS)
+ return -EMSGSIZE;
get_page(page);
skb_fill_page_desc(skb, i, page, offset, size);
} else {
--
2.34.1
