The patch titled Subject: highmem: add folio_test_partial_kmap() has been added to the -mm mm-hotfixes-unstable branch. Its filename is highmem-add-folio_test_partial_kmap.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days
------------------------------------------------------ From: "Matthew Wilcox (Oracle)" willy@infradead.org Subject: highmem: add folio_test_partial_kmap() Date: Wed, 14 May 2025 18:06:02 +0100
In commit c749d9b7ebbc (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: 00cdf76012ab ("mm: add memcpy_from_file_folio()") Signed-off-by: Matthew 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: Andrew Morton akpm@linux-foundation.org ---
include/linux/highmem.h | 10 +++++----- include/linux/page-flags.h | 7 +++++++ 2 files changed, 12 insertions(+), 5 deletions(-)
--- a/include/linux/highmem.h~highmem-add-folio_test_partial_kmap +++ a/include/linux/highmem.h @@ -461,7 +461,7 @@ static inline void memcpy_from_folio(cha 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(struc 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_z { 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(struc
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_fo 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 --- a/include/linux/page-flags.h~highmem-add-folio_test_partial_kmap +++ a/include/linux/page-flags.h @@ -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) { _
Patches currently in -mm which might be from willy@infradead.org are
highmem-add-folio_test_partial_kmap.patch mm-rename-page-index-to-page-__folio_index.patch