Commit 97dfbbd1 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

highmem: add folio_test_partial_kmap() 

In commit c749d9b7 ("iov_iter: fix copy_page_from_iter_atomic() if
KMAP_LOCAL_FORCE_MAP"), Hugh correctly noted that if KMAP_LOCAL_FORCE_MAP
is enabled, we must limit ourselves to PAGE_SIZE bytes per call to
kmap_local().  The same problem exists in memcpy_from_folio(),
memcpy_to_folio(), folio_zero_tail(), folio_fill_tail() and
memcpy_from_file_folio(), so add folio_test_partial_kmap() to do this more
succinctly.

Link: https://lkml.kernel.org/r/20250514170607.3000994-2-willy@infradead.org


Fixes: 00cdf760 ("mm: add memcpy_from_file_folio()")
Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6fa04511

include/linux/highmem.h

+5 −5
Original line number Diff line number Diff line
@@ -461,7 +461,7 @@ static inline void memcpy_from_folio(char *to, struct folio *folio, 
		const char *from = kmap_local_folio(folio, offset);

		size_t chunk = len;



		if (folio_test_highmem(folio) &&

		if (folio_test_partial_kmap(folio) &&

		    chunk > PAGE_SIZE - offset_in_page(offset))

			chunk = PAGE_SIZE - offset_in_page(offset);

		memcpy(to, from, chunk);
@@ -489,7 +489,7 @@ static inline void memcpy_to_folio(struct folio *folio, size_t offset, 
		char *to = kmap_local_folio(folio, offset);

		size_t chunk = len;



		if (folio_test_highmem(folio) &&

		if (folio_test_partial_kmap(folio) &&

		    chunk > PAGE_SIZE - offset_in_page(offset))

			chunk = PAGE_SIZE - offset_in_page(offset);

		memcpy(to, from, chunk);
@@ -522,7 +522,7 @@ static inline __must_check void *folio_zero_tail(struct folio *folio, 
{

	size_t len = folio_size(folio) - offset;



	if (folio_test_highmem(folio)) {

	if (folio_test_partial_kmap(folio)) {

		size_t max = PAGE_SIZE - offset_in_page(offset);



		while (len > max) {
@@ -560,7 +560,7 @@ static inline void folio_fill_tail(struct folio *folio, size_t offset, 


	VM_BUG_ON(offset + len > folio_size(folio));



	if (folio_test_highmem(folio)) {

	if (folio_test_partial_kmap(folio)) {

		size_t max = PAGE_SIZE - offset_in_page(offset);



		while (len > max) {
@@ -597,7 +597,7 @@ static inline size_t memcpy_from_file_folio(char *to, struct folio *folio, 
	size_t offset = offset_in_folio(folio, pos);

	char *from = kmap_local_folio(folio, offset);



	if (folio_test_highmem(folio)) {

	if (folio_test_partial_kmap(folio)) {

		offset = offset_in_page(offset);

		len = min_t(size_t, len, PAGE_SIZE - offset);

	} else

include/linux/page-flags.h

+7 −0
Original line number Diff line number Diff line
@@ -615,6 +615,13 @@ FOLIO_FLAG(dropbehind, FOLIO_HEAD_PAGE) 
PAGEFLAG_FALSE(HighMem, highmem)

#endif



/* Does kmap_local_folio() only allow access to one page of the folio? */

#ifdef CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP

#define folio_test_partial_kmap(f)	true

#else

#define folio_test_partial_kmap(f)	folio_test_highmem(f)

#endif



#ifdef CONFIG_SWAP

static __always_inline bool folio_test_swapcache(const struct folio *folio)

{