[PATCH RFC 32/35] mm/gup: drop nth_page() usage in unpin_user_page_range_dirty_lock()
From: David Hildenbrand <hidden>
Date: 2025-08-21 20:12:41
Also in:
dri-devel, intel-gfx, io-uring, kvm, linux-arm-kernel, linux-crypto, linux-ide, linux-iommu, linux-kselftest, linux-mips, linux-mm, linux-mmc, linux-riscv, linux-s390, linux-scsi, lkml, virtualization
Subsystem:
memory management, memory management - gup (get user pages), the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
There is the concern that unpin_user_page_range_dirty_lock() might do some weird merging of PFN ranges -- either now or in the future -- such that PFN range is contiguous but the page range might not be. Let's sanity-check for that and drop the nth_page() usage. Signed-off-by: David Hildenbrand <redacted> --- mm/gup.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/gup.c b/mm/gup.c
index f017ff6d7d61a..0a669a766204b 100644
--- a/mm/gup.c
+++ b/mm/gup.c@@ -237,7 +237,7 @@ void folio_add_pin(struct folio *folio) static inline struct folio *gup_folio_range_next(struct page *start, unsigned long npages, unsigned long i, unsigned int *ntails) { - struct page *next = nth_page(start, i); + struct page *next = start + i; struct folio *folio = page_folio(next); unsigned int nr = 1;
@@ -342,6 +342,9 @@ EXPORT_SYMBOL(unpin_user_pages_dirty_lock); * "gup-pinned page range" refers to a range of pages that has had one of the * pin_user_pages() variants called on that page. * + * The page range must be truly contiguous: the page range corresponds + * to a contiguous PFN range and all pages can be iterated naturally. + * * For the page ranges defined by [page .. page+npages], make that range (or * its head pages, if a compound page) dirty, if @make_dirty is true, and if the * page range was previously listed as clean.
@@ -359,6 +362,8 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages, struct folio *folio; unsigned int nr; + VM_WARN_ON_ONCE(!page_range_contiguous(page, npages)); + for (i = 0; i < npages; i += nr) { folio = gup_folio_range_next(page, npages, i, &nr); if (make_dirty && !folio_test_dirty(folio)) {
--
2.50.1