From 311150343e69ed4fe6380d2de74602a2a29df7c2 Mon Sep 17 00:00:00 2001 From: Lorenzo Stoakes Date: Sat, 6 May 2023 15:05:25 +0100 Subject: [PATCH] mm/gup: add missing gup_must_unshare() check to gup_huge_pgd() All other instances of gup_huge_pXd() perform the unshare check, so update the PGD-specific function to do so as well. While checking pgd_write() might seem unusual, this function already performs such a check via pgd_access_permitted() so this is in line with the existing implementation. David said: : This change makes unshare handling across all GUP-fast variants : consistent, which is desirable as GUP-fast is complicated enough : already even when consistent. : : This function was the only one I seemed to have missed (or left out and : forgot why -- maybe because it's really dead code for now). The COW : selftest would identify the problem, so far there was no report. : Either the selftest wasn't run on corresponding architectures with that : hugetlb size, or that code is still dead code and unused by : architectures. : : the original commit(s) that added unsharing explain why we care about : these checks: : : a7f226604170acd6 ("mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page") : 84209e87c6963f92 ("mm/gup: reliable R/O long-term pinning in COW mappings") Link: https://lkml.kernel.org/r/cb971ac8dd315df97058ea69442ecc007b9a364a.1683381545.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes Suggested-by: David Hildenbrand Acked-by: David Hildenbrand Signed-off-by: Andrew Morton --- mm/gup.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/gup.c b/mm/gup.c index bbe4162..e19b06a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2755,6 +2755,11 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, return 0; } + if (!pgd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) { + gup_put_folio(folio, refs, flags); + return 0; + } + *nr += refs; folio_set_referenced(folio); return 1; -- 2.7.4