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Date: Thu, 29 Jun 2017 12:12:38 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net, Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH rfc net-next] net: add skb_frag_foreach_page and use with kmap_atomic
From: Willem de Bruijn <willemb@...gle.com>
Skb frags may contain compound pages. Various operations map frags
temporarily using kmap_atomic, but this function works on single
pages, not whole compound pages. The distinction is only relevant
for high mem pages that require temporary mappings.
Introduce a looping mechanism that for compound highmem pages maps
one page at a time, does not change behavior on other pages.
Use the loop in the kmap_atomic callers in net/core/skbuff.c.
Verified by triggering skb_copy_bits with
tcpdump -n -c 100 -i ${DEV} -w /dev/null &
netperf -t TCP_STREAM -H ${HOST}
and by triggering __skb_checksum with
ethtool -K ${DEV} tx off
repeated the tests with looping on a non-highmem platform
(x86_64) by making skb_frag_must_loop always return true.
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
include/linux/skbuff.h | 36 +++++++++++++++++++++
net/core/skbuff.c | 88 +++++++++++++++++++++++++++++++++-----------------
2 files changed, 95 insertions(+), 29 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index a17e235639ae..6bf3280dfd37 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -345,6 +345,42 @@ static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
frag->size -= delta;
}
+static inline bool skb_frag_must_loop(struct page *p)
+{
+#if defined(CONFIG_HIGHMEM)
+ if (PageHighMem(p))
+ return true;
+#endif
+ return false;
+}
+
+/**
+ * skb_frag_foreach_page - loop over pages in a fragment
+ *
+ * @f: skb frag to operate on
+ * @f_off: offset from start of f->page.p
+ * @f_len: length from f_off to loop over
+ * @p: (temp var) current page
+ * @p_off: (temp var) offset from start of current page,
+ * non-zero only on first page.
+ * @p_len: (temp var) length in current page,
+ * < PAGE_SIZE only on first and last page.
+ * @copied: (temp var) length so far, excluding current p_len.
+ *
+ * A fragment can hold a compound page, in which case per-page
+ * operations, notably kmap_atomic, must be called for each
+ * regular page.
+ */
+#define skb_frag_foreach_page(f, f_off, f_len, p, p_off, p_len, copied) \
+ for (p = skb_frag_page(f) + ((f_off) >> PAGE_SHIFT), \
+ p_off = (f_off) & (PAGE_SIZE - 1), \
+ p_len = skb_frag_must_loop(p) ? \
+ min_t(u32, f_len, PAGE_SIZE - p_off) : f_len, \
+ copied = 0; \
+ copied < f_len; \
+ copied += p_len, p++, p_off = 0, \
+ p_len = min_t(u32, f_len - copied, PAGE_SIZE)) \
+
#define HAVE_HW_TIME_STAMP
/**
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f75897a33fa4..42d49c5c3cb9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -964,8 +964,10 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
struct ubuf_info *uarg = skb_shinfo(skb)->destructor_arg;
for (i = 0; i < num_frags; i++) {
- u8 *vaddr;
skb_frag_t *f = &skb_shinfo(skb)->frags[i];
+ u32 p_off, p_len, copied;
+ struct page *p;
+ u8 *vaddr;
page = alloc_page(gfp_mask);
if (!page) {
@@ -976,10 +978,15 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
}
return -ENOMEM;
}
- vaddr = kmap_atomic(skb_frag_page(f));
- memcpy(page_address(page),
- vaddr + f->page_offset, skb_frag_size(f));
- kunmap_atomic(vaddr);
+
+ skb_frag_foreach_page(f, f->page_offset, skb_frag_size(f),
+ p, p_off, p_len, copied) {
+ vaddr = kmap_atomic(p);
+ memcpy(page_address(page) + copied, vaddr + p_off,
+ p_len);
+ kunmap_atomic(vaddr);
+ }
+
set_page_private(page, (unsigned long)head);
head = page;
}
@@ -1776,16 +1783,20 @@ int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
end = start + skb_frag_size(f);
if ((copy = end - offset) > 0) {
+ u32 p_off, p_len, copied;
+ struct page *p;
u8 *vaddr;
if (copy > len)
copy = len;
- vaddr = kmap_atomic(skb_frag_page(f));
- memcpy(to,
- vaddr + f->page_offset + offset - start,
- copy);
- kunmap_atomic(vaddr);
+ skb_frag_foreach_page(f,
+ f->page_offset + offset - start,
+ copy, p, p_off, p_len, copied) {
+ vaddr = kmap_atomic(p);
+ memcpy(to + copied, vaddr + p_off, p_len);
+ kunmap_atomic(vaddr);
+ }
if ((len -= copy) == 0)
return 0;
@@ -2044,15 +2055,20 @@ int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len)
end = start + skb_frag_size(frag);
if ((copy = end - offset) > 0) {
+ u32 p_off, p_len, copied;
+ struct page *p;
u8 *vaddr;
if (copy > len)
copy = len;
- vaddr = kmap_atomic(skb_frag_page(frag));
- memcpy(vaddr + frag->page_offset + offset - start,
- from, copy);
- kunmap_atomic(vaddr);
+ skb_frag_foreach_page(frag,
+ frag->page_offset + offset - start,
+ copy, p, p_off, p_len, copied) {
+ vaddr = kmap_atomic(p);
+ memcpy(vaddr + p_off, from + copied, p_len);
+ kunmap_atomic(vaddr);
+ }
if ((len -= copy) == 0)
return 0;
@@ -2117,20 +2133,27 @@ __wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
end = start + skb_frag_size(frag);
if ((copy = end - offset) > 0) {
+ u32 p_off, p_len, copied;
+ struct page *p;
__wsum csum2;
u8 *vaddr;
if (copy > len)
copy = len;
- vaddr = kmap_atomic(skb_frag_page(frag));
- csum2 = ops->update(vaddr + frag->page_offset +
- offset - start, copy, 0);
- kunmap_atomic(vaddr);
- csum = ops->combine(csum, csum2, pos, copy);
+
+ skb_frag_foreach_page(frag,
+ frag->page_offset + offset - start,
+ copy, p, p_off, p_len, copied) {
+ vaddr = kmap_atomic(p);
+ csum2 = ops->update(vaddr + p_off, p_len, 0);
+ kunmap_atomic(vaddr);
+ csum = ops->combine(csum, csum2, pos, p_len);
+ pos += p_len;
+ }
+
if (!(len -= copy))
return csum;
offset += copy;
- pos += copy;
}
start = end;
}
@@ -2203,24 +2226,31 @@ __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset,
end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
if ((copy = end - offset) > 0) {
+ skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+ u32 p_off, p_len, copied;
+ struct page *p;
__wsum csum2;
u8 *vaddr;
- skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
if (copy > len)
copy = len;
- vaddr = kmap_atomic(skb_frag_page(frag));
- csum2 = csum_partial_copy_nocheck(vaddr +
- frag->page_offset +
- offset - start, to,
- copy, 0);
- kunmap_atomic(vaddr);
- csum = csum_block_add(csum, csum2, pos);
+
+ skb_frag_foreach_page(frag,
+ frag->page_offset + offset - start,
+ copy, p, p_off, p_len, copied) {
+ vaddr = kmap_atomic(p);
+ csum2 = csum_partial_copy_nocheck(vaddr + p_off,
+ to + copied,
+ p_len, 0);
+ kunmap_atomic(vaddr);
+ csum = csum_block_add(csum, csum2, pos);
+ pos += p_len;
+ }
+
if (!(len -= copy))
return csum;
offset += copy;
to += copy;
- pos += copy;
}
start = end;
}
--
2.13.2.725.g09c95d1e9-goog
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