mm/highmem: Lift memcpy_[to|from]_page to core

[ Upstream commit baf49f20f9d52b5a36e36dab5a56425c589ade84 ]

Working through a conversion to a call kmap_local_page() instead of
kmap() revealed many places where the pattern kmap/memcpy/kunmap
occurred.

Eric Biggers, Matthew Wilcox, Christoph Hellwig, Dan Williams, and Al
Viro all suggested putting this code into helper functions.  Al Viro
further pointed out that these functions already existed in the iov_iter
code.[1]

Various locations for the lifted functions were considered.

Headers like mm.h or string.h seem ok but don't really portray the
functionality well.  pagemap.h made some sense but is for page cache
functionality.[2]

Another alternative would be to create a new header for the promoted
memcpy functions, but it masks the fact that these are designed to copy
to/from pages using the kernel direct mappings and complicates matters
with a new header.

Placing these functions in 'highmem.h' is suboptimal especially with the
changes being proposed in the functionality of kmap.  From a caller
perspective including/using 'highmem.h' implies that the functions
defined in that header are only required when highmem is in use which is
increasingly not the case with modern processors.  However, highmem.h is
where all the current functions like this reside (zero_user(),
clear_highpage(), clear_user_highpage(), copy_user_highpage(), and
copy_highpage()).  So it makes the most sense even though it is
distasteful for some.[3]

Lift memcpy_to_page() and memcpy_from_page() to pagemap.h.

[1] https://lore.kernel.org/lkml/20201013200149.GI3576660@ZenIV.linux.org.uk/
    https://lore.kernel.org/lkml/20201013112544.GA5249@infradead.org/

[2] https://lore.kernel.org/lkml/20201208122316.GH7338@casper.infradead.org/

[3] https://lore.kernel.org/lkml/20201013200149.GI3576660@ZenIV.linux.org.uk/#t
    https://lore.kernel.org/lkml/20201208163814.GN1563847@iweiny-DESK2.sc.intel.com/

Cc: Boris Pismenny <borisp@mellanox.com>
Cc: Or Gerlitz <gerlitz.or@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: 956510c0c743 ("fs: ext4: initialize fsdata in pagecache_write()")
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index ea5cdbd8c2c326cd6f8702bfc2e6aa2e9fbca2c0..900f224bb6401a2509844ef011bd219139ecb639 100644 (file)
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -276,4 +276,22 @@ static inline void copy_highpage(struct page *to, struct page *from)
 
 #endif
 
+static inline void memcpy_from_page(char *to, struct page *page,
+                                   size_t offset, size_t len)
+{
+       char *from = kmap_atomic(page);
+
+       memcpy(to, from + offset, len);
+       kunmap_atomic(from);
+}
+
+static inline void memcpy_to_page(struct page *page, size_t offset,
+                                 const char *from, size_t len)
+{
+       char *to = kmap_atomic(page);
+
+       memcpy(to + offset, from, len);
+       kunmap_atomic(to);
+}
+
 #endif /* _LINUX_HIGHMEM_H */

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 9d3bda3d49feddc0e19f2baf2856d7e5f95c012e..5c6a0b8a2adbb71d39f29b4fa5625be3f28e3420 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -455,20 +455,6 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction,
 }
 EXPORT_SYMBOL(iov_iter_init);
 
-static void memcpy_from_page(char *to, struct page *page, size_t offset, size_t len)
-{
-       char *from = kmap_atomic(page);
-       memcpy(to, from + offset, len);
-       kunmap_atomic(from);
-}
-
-static void memcpy_to_page(struct page *page, size_t offset, const char *from, size_t len)
-{
-       char *to = kmap_atomic(page);
-       memcpy(to + offset, from, len);
-       kunmap_atomic(to);
-}
-
 static void memzero_page(struct page *page, size_t offset, size_t len)
 {
        char *addr = kmap_atomic(page);