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Sun, 24 May 2026 19:52:34 -0700 (PDT) From: Muchun Song To: Muchun Song , Oscar Salvador , Andrew Morton Cc: David Hildenbrand , Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Muchun Song Subject: [PATCH] mm/hugetlb_vmemmap: fix incorrect vmemmap restore in rollback Date: Mon, 25 May 2026 10:52:13 +0800 Message-ID: <20260525025213.2229628-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" vmemmap_restore_pte() rebuilds restored vmemmap pages from a tail-page template derived from compound_head(). This is wrong when the current PTE already maps a page whose contents are not tail-page metadata. In the rollback path of vmemmap_remap_free(), the first restored PTE is backed by vmemmap_head and contains head-page metadata. Reconstructing that page from a tail-page template overwrites the head-page state and corrupts the restored vmemmap page. Fix this by copying the full page from the page currently mapped by the PTE. Also pass vmemmap_tail to the rollback walk so only PTEs backed by the shared tail page are restored, while the head PTE remains mapped to vmemmap_head. Add VM_WARN_ON_ONCE() checks for unexpected cases. Fixes: c0b495b91a47 ("mm/hugetlb: refactor code around vmemmap_walk") Cc: stable@vger.kernel.org Signed-off-by: Muchun Song Acked-by: Kiryl Shutsemau Acked-by: Oscar Salvador (SUSE) --- mm/hugetlb_vmemmap.c | 36 ++++++++++++++++++------------------ 1 file changed, 18 insertions(+), 18 deletions(-) diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index 4a077d231d3a..133b46dfb09f 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -207,6 +207,8 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long= addr, =20 /* Remapping the head page requires r/w */ if (unlikely(walk->nr_walked =3D=3D 0 && walk->vmemmap_head)) { + VM_WARN_ON_ONCE(!PageHead((const struct page *)addr)); + list_del(&walk->vmemmap_head->lru); =20 /* @@ -218,6 +220,8 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long= addr, =20 entry =3D mk_pte(walk->vmemmap_head, PAGE_KERNEL); } else { + VM_WARN_ON_ONCE(!PageTail((const struct page *)addr)); + /* * Remap the tail pages as read-only to catch illegal write * operation to the tail pages. @@ -232,33 +236,28 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned lo= ng addr, static void vmemmap_restore_pte(pte_t *pte, unsigned long addr, struct vmemmap_remap_walk *walk) { - struct page *page; - struct page *from, *to; - - page =3D list_first_entry(walk->vmemmap_pages, struct page, lru); - list_del(&page->lru); + struct page *src =3D pte_page(ptep_get(pte)), *dst; =20 /* - * Initialize tail pages in the newly allocated vmemmap page. - * - * There is folio-scope metadata that is encoded in the first few - * tail pages. - * - * Use the value last tail page in the page with the head page - * to initialize the rest of tail pages. + * When rolling back vmemmap_remap_free(), keep the copied head page + * mapping and restore only PTEs currently pointing at the shared tail + * page. */ - from =3D compound_head((struct page *)addr) + - PAGE_SIZE / sizeof(struct page) - 1; - to =3D page_to_virt(page); - for (int i =3D 0; i < PAGE_SIZE / sizeof(struct page); i++, to++) - *to =3D *from; + if (walk->vmemmap_tail && walk->vmemmap_tail !=3D src) + return; + + VM_WARN_ON_ONCE(PageHead((const struct page *)addr)); + + dst =3D list_first_entry(walk->vmemmap_pages, struct page, lru); + list_del(&dst->lru); + copy_page(page_to_virt(dst), page_to_virt(src)); =20 /* * Makes sure that preceding stores to the page contents become visible * before the set_pte_at() write. */ smp_wmb(); - set_pte_at(&init_mm, addr, pte, mk_pte(page, PAGE_KERNEL)); + set_pte_at(&init_mm, addr, pte, mk_pte(dst, PAGE_KERNEL)); } =20 /** @@ -324,6 +323,7 @@ static int vmemmap_remap_free(unsigned long start, unsi= gned long end, */ walk =3D (struct vmemmap_remap_walk) { .remap_pte =3D vmemmap_restore_pte, + .vmemmap_tail =3D vmemmap_tail, .vmemmap_pages =3D vmemmap_pages, .flags =3D 0, }; base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83 --=20 2.54.0