The quilt patch titled Subject: mm: hugetlb_vmemmap: fix a race between vmemmap pmd split has been removed from the -mm tree. Its filename was mm-hugetlb_vmemmap-fix-a-race-between-vmemmap-pmd-split.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------ From: Muchun Song songmuchun@bytedance.com Subject: mm: hugetlb_vmemmap: fix a race between vmemmap pmd split Date: Fri, 7 Jul 2023 11:38:59 +0800

The local variable @page in __split_vmemmap_huge_pmd() to obtain a pmd page without holding page_table_lock may possiblely get the page table page instead of a huge pmd page.

The effect may be in set_pte_at() since we may pass an invalid page struct, if set_pte_at() wants to access the page struct (e.g. CONFIG_PAGE_TABLE_CHECK is enabled), it may crash the kernel.

So fix it. And inline __split_vmemmap_huge_pmd() since it only has one user.

Link: https://lkml.kernel.org/r/20230707033859.16148-1-songmuchun@bytedance.com Fixes: d8d55f5616cf ("mm: sparsemem: use page table lock to protect kernel pmd operations") Signed-off-by: Muchun Song songmuchun@bytedance.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hugetlb_vmemmap.c | 34 ++++++++++++++-------------------- 1 file changed, 14 insertions(+), 20 deletions(-)

--- a/mm/hugetlb_vmemmap.c~mm-hugetlb_vmemmap-fix-a-race-between-vmemmap-pmd-split +++ a/mm/hugetlb_vmemmap.c @@ -36,14 +36,22 @@ struct vmemmap_remap_walk { struct list_head *vmemmap_pages; };

-static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start) +static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start) { pmd_t __pmd; int i; unsigned long addr = start; - struct page *page = pmd_page(*pmd); - pte_t *pgtable = pte_alloc_one_kernel(&init_mm); + struct page *head; + pte_t *pgtable; + + spin_lock(&init_mm.page_table_lock); + head = pmd_leaf(*pmd) ? pmd_page(*pmd) : NULL; + spin_unlock(&init_mm.page_table_lock);

+ if (!head) + return 0; + + pgtable = pte_alloc_one_kernel(&init_mm); if (!pgtable) return -ENOMEM;

@@ -53,7 +61,7 @@ static int __split_vmemmap_huge_pmd(pmd_ pte_t entry, *pte; pgprot_t pgprot = PAGE_KERNEL;

- entry = mk_pte(page + i, pgprot); + entry = mk_pte(head + i, pgprot); pte = pte_offset_kernel(&__pmd, addr); set_pte_at(&init_mm, addr, pte, entry); } @@ -65,8 +73,8 @@ static int __split_vmemmap_huge_pmd(pmd_ * be treated as indepdenent small pages (as they can be freed * individually). */ - if (!PageReserved(page)) - split_page(page, get_order(PMD_SIZE)); + if (!PageReserved(head)) + split_page(head, get_order(PMD_SIZE));

/* Make pte visible before pmd. See comment in pmd_install(). */ smp_wmb(); @@ -80,20 +88,6 @@ static int __split_vmemmap_huge_pmd(pmd_ return 0; }

-static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start) -{ - int leaf; - - spin_lock(&init_mm.page_table_lock); - leaf = pmd_leaf(*pmd); - spin_unlock(&init_mm.page_table_lock); - - if (!leaf) - return 0; - - return __split_vmemmap_huge_pmd(pmd, start); -} - static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, struct vmemmap_remap_walk *walk) _

Patches currently in -mm which might be from songmuchun@bytedance.com are