From: Ira Weiny <ira.weiny@xxxxxxxxx> 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. Remove memzero_page() in favor of zero_user() to zero a page. Add a memcpy_page(), memmove_page, and memset_page() to cover more kmap/mem*/kunmap. patterns. Add BUG_ON bounds checks to ensure the newly lifted page memory operations do not result in corrupted data in neighbor pages and to make them consistent with zero_user().[4] Finally use kmap_local_page() in all the new calls. [1] https://lore.kernel.org/lkml/20201013200149.GI3576660@xxxxxxxxxxxxxxxxxx/ https://lore.kernel.org/lkml/20201013112544.GA5249@xxxxxxxxxxxxx/ [2] https://lore.kernel.org/lkml/20201208122316.GH7338@xxxxxxxxxxxxxxxxxxxx/ [3] https://lore.kernel.org/lkml/20201013200149.GI3576660@xxxxxxxxxxxxxxxxxx/#t https://lore.kernel.org/lkml/20201208163814.GN1563847@xxxxxxxxxxxxxxxxxxxxxxxxx/ [4] https://lore.kernel.org/lkml/20201210053502.GS1563847@xxxxxxxxxxxxxxxxxxxxxxxxx/ Cc: Boris Pismenny <borisp@xxxxxxxxxxxx> Cc: Or Gerlitz <gerlitz.or@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx> Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx> Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Suggested-by: Eric Biggers <ebiggers@xxxxxxxxxx> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx> --- Chagnes for V4: Update commit message to say kmap_local_page() since kmap_thread() is no longer valid Changes for V3: From Matthew Wilcox Move calls to highmem.h Add BUG_ON() Changes for V2: From Thomas Gleixner Change kmap_atomic() to kmap_local_page() after basing on tip/core/mm From Joonas Lahtinen Reverse offset/val in memset_page() --- include/linux/highmem.h | 53 +++++++++++++++++++++++++++++++++++++++++ lib/iov_iter.c | 26 +++----------------- 2 files changed, 56 insertions(+), 23 deletions(-) diff --git a/include/linux/highmem.h b/include/linux/highmem.h index d2c70d3772a3..c642dd64ea3f 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -276,4 +276,57 @@ static inline void copy_highpage(struct page *to, struct page *from) #endif +static inline void memcpy_page(struct page *dst_page, size_t dst_off, + struct page *src_page, size_t src_off, + size_t len) +{ + char *dst = kmap_local_page(dst_page); + char *src = kmap_local_page(src_page); + + BUG_ON(dst_off + len > PAGE_SIZE || src_off + len > PAGE_SIZE); + memcpy(dst + dst_off, src + src_off, len); + kunmap_local(src); + kunmap_local(dst); +} + +static inline void memmove_page(struct page *dst_page, size_t dst_off, + struct page *src_page, size_t src_off, + size_t len) +{ + char *dst = kmap_local_page(dst_page); + char *src = kmap_local_page(src_page); + + BUG_ON(dst_off + len > PAGE_SIZE || src_off + len > PAGE_SIZE); + memmove(dst + dst_off, src + src_off, len); + kunmap_local(src); + kunmap_local(dst); +} + +static inline void memcpy_from_page(char *to, struct page *page, size_t offset, size_t len) +{ + char *from = kmap_local_page(page); + + BUG_ON(offset + len > PAGE_SIZE); + memcpy(to, from + offset, len); + kunmap_local(from); +} + +static inline void memcpy_to_page(struct page *page, size_t offset, const char *from, size_t len) +{ + char *to = kmap_local_page(page); + + BUG_ON(offset + len > PAGE_SIZE); + memcpy(to + offset, from, len); + kunmap_local(to); +} + +static inline void memset_page(struct page *page, size_t offset, int val, size_t len) +{ + char *addr = kmap_local_page(page); + + BUG_ON(offset + len > PAGE_SIZE); + memset(addr + offset, val, len); + kunmap_local(addr); +} + #endif /* _LINUX_HIGHMEM_H */ diff --git a/lib/iov_iter.c b/lib/iov_iter.c index a21e6a5792c5..aa0d03b33a1e 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -5,6 +5,7 @@ #include <linux/fault-inject-usercopy.h> #include <linux/uio.h> #include <linux/pagemap.h> +#include <linux/highmem.h> #include <linux/slab.h> #include <linux/vmalloc.h> #include <linux/splice.h> @@ -466,27 +467,6 @@ 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); - memset(addr + offset, 0, len); - kunmap_atomic(addr); -} - static inline bool allocated(struct pipe_buffer *buf) { return buf->ops == &default_pipe_buf_ops; @@ -964,7 +944,7 @@ static size_t pipe_zero(size_t bytes, struct iov_iter *i) do { size_t chunk = min_t(size_t, n, PAGE_SIZE - off); - memzero_page(pipe->bufs[i_head & p_mask].page, off, chunk); + zero_user(pipe->bufs[i_head & p_mask].page, off, chunk); i->head = i_head; i->iov_offset = off + chunk; n -= chunk; @@ -981,7 +961,7 @@ size_t iov_iter_zero(size_t bytes, struct iov_iter *i) return pipe_zero(bytes, i); iterate_and_advance(i, bytes, v, clear_user(v.iov_base, v.iov_len), - memzero_page(v.bv_page, v.bv_offset, v.bv_len), + zero_user(v.bv_page, v.bv_offset, v.bv_len), memset(v.iov_base, 0, v.iov_len) ) -- 2.28.0.rc0.12.gb6a658bd00c9
