linux-kernel - [PATCH] mm/gup: add missing gup_must_unshare() check to gup_huge

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Message-Id: <cb971ac8dd315df97058ea69442ecc007b9a364a.1683381545.git.lstoakes@gmail.com>
Date:   Sat,  6 May 2023 15:05:25 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Lorenzo Stoakes <lstoakes@...il.com>
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.

Suggested-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
---
 mm/gup.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index ef43ffb3d1fe..78a5198e3212 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2898,6 +2898,11 @@ 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;
-- 
2.40.1