From: Ira Weiny <ira.weiny@xxxxxxxxx> Subject: highmem: document kunmap_local() Some users of kmap() add an offset to the kmap() address to be used during the mapping. When converting to kmap_local_page() the base address does not need to be stored because any address within the page can be used in kunmap_local(). However, this was not clear from the documentation and cause some questions.[1] Document that any address in the page can be used in kunmap_local() to clarify this for future users. [1] https://lore.kernel.org/lkml/20211213154543.GM3538886@xxxxxxxxxxxxxxxxxxxxxxxxx/ [ira.weiny@xxxxxxxxx: updates per Christoph] Link: https://lkml.kernel.org/r/20220124182138.816693-1-ira.weiny@xxxxxxxxx Link: https://lkml.kernel.org/r/20220124013045.806718-1-ira.weiny@xxxxxxxxx Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/highmem-internal.h | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/include/linux/highmem-internal.h~highmem-document-kunmap_local +++ a/include/linux/highmem-internal.h @@ -246,6 +246,16 @@ do { \ __kunmap_atomic(__addr); \ } while (0) +/** + * kunmap_local - Unmap a page mapped via kmap_local_page(). + * @__addr: An address within the page mapped + * + * @__addr can be any address within the mapped page. Commonly it is the + * address return from kmap_local_page(), but it can also include offsets. + * + * Unmapping should be done in the reverse order of the mapping. See + * kmap_local_page() for details. + */ #define kunmap_local(__addr) \ do { \ BUILD_BUG_ON(__same_type((__addr), struct page *)); \ _
