[PATCH v3 net-next 01/21] iov_iter: Introduce new procedures for copy to iter/pages

[Boris Pismenny]

When using direct data placement the NIC writes some of the payload
directly to the destination buffer, and constructs the SKB such that it
points to this data. As a result, the skb_copy datagram_iter call will
attempt to copy data when it is not necessary.

Introduce new procedures for copy to iter/pages in case that the
source of the copy operation might be identical to the destination,
in such cases the copy is skipped only for bio_vec, later commits
uses those functions to introduce new skb copy(+hash) functions.

Signed-off-by: Boris Pismenny <borisp at mellanox.com>
Signed-off-by: Ben Ben-Ishay <benishay at mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz at mellanox.com>
Signed-off-by: Yoray Zack <yorayz at mellanox.com>
---
 include/linux/uio.h | 12 ++++++++++++
 lib/iov_iter.c      | 47 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 72d88566694e..3c42125a7f24 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -123,6 +123,7 @@ size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);
 
 size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
+size_t _ddp_copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
 size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
 bool _copy_from_iter_full(void *addr, size_t bytes, struct iov_iter *i);
 size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i);
@@ -137,6 +138,15 @@ size_t copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 		return _copy_to_iter(addr, bytes, i);
 }
 
+static __always_inline __must_check
+size_t ddp_copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
+{
+	if (unlikely(!check_copy_size(addr, bytes, true)))
+		return 0;
+	else
+		return _ddp_copy_to_iter(addr, bytes, i);
+}
+
 static __always_inline __must_check
 size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 {
@@ -265,6 +275,8 @@ size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum, struct io
 bool csum_and_copy_from_iter_full(void *addr, size_t bytes, __wsum *csum, struct iov_iter *i);
 size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
 		struct iov_iter *i);
+size_t ddp_hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
+		struct iov_iter *i);
 
 struct iovec *iovec_from_user(const struct iovec __user *uvector,
 		unsigned long nr_segs, unsigned long fast_segs,
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index a21e6a5792c5..b8af1d3bbec0 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -473,6 +473,16 @@ static void memcpy_from_page(char *to, struct page *page, size_t offset, size_t
 	kunmap_atomic(from);
 }
 
+static void ddp_memcpy_to_page(struct page *page, size_t offset, const char *from, size_t len)
+{
+	char *to = kmap_atomic(page);
+
+	if (to + offset != from)
+		memcpy(to + offset, from, len);
+
+	kunmap_atomic(to);
+}
+
 static void memcpy_to_page(struct page *page, size_t offset, const char *from, size_t len)
 {
 	char *to = kmap_atomic(page);
@@ -625,6 +635,24 @@ static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
 	return bytes;
 }
 
+size_t _ddp_copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
+{
+	const char *from = addr;
+	if (unlikely(iov_iter_is_pipe(i)))
+		return copy_pipe_to_iter(addr, bytes, i);
+	if (iter_is_iovec(i))
+		might_fault();
+	iterate_and_advance(i, bytes, v,
+		copyout(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len),
+		ddp_memcpy_to_page(v.bv_page, v.bv_offset,
+				   (from += v.bv_len) - v.bv_len, v.bv_len),
+		memcpy(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len)
+		)
+
+	return bytes;
+}
+EXPORT_SYMBOL(_ddp_copy_to_iter);
+
 size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 {
 	const char *from = addr;
@@ -1566,6 +1594,25 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *csump,
 }
 EXPORT_SYMBOL(csum_and_copy_to_iter);
 
+size_t ddp_hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
+		struct iov_iter *i)
+{
+#ifdef CONFIG_CRYPTO_HASH
+	struct ahash_request *hash = hashp;
+	struct scatterlist sg;
+	size_t copied;
+
+	copied = ddp_copy_to_iter(addr, bytes, i);
+	sg_init_one(&sg, addr, copied);
+	ahash_request_set_crypt(hash, &sg, NULL, copied);
+	crypto_ahash_update(hash);
+	return copied;
+#else
+	return 0;
+#endif
+}
+EXPORT_SYMBOL(ddp_hash_and_copy_to_iter);
+
 size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
 		struct iov_iter *i)
 {
-- 
2.24.1