| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 118/120] arm64: hugetlb: remove the wrong pmd check in find_num_contig() | Date | Wed, 18 Jan 2017 11:47:16 +0100 |
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4.9-stable review patch. If anyone has any objections, please let me know.
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From: Huang Shijie <shijie.huang@arm.com>
commit 20156ce2365d61beaa6f5a78a7a789044e0e7acc upstream.
The find_num_contig() will return 1 when the pmd is not present. It will cause a kernel dead loop in the following scenaro:
1.) pmd entry is not present.
2.) the page fault occurs: ... hugetlb_fault() --> hugetlb_no_page() --> set_huge_pte_at()
3.) set_huge_pte_at() will only set the first PMD entry, since the find_num_contig just return 1 in this case. So the PMD entries are all empty except the first one.
4.) when kernel accesses the address mapped by the second PMD entry, a new page fault occurs: ... hugetlb_fault() --> huge_ptep_set_access_flags()
The second PMD entry is still empty now.
5.) When the kernel returns, the access will cause a page fault again. The kernel will run like the "4)" above. We will see a dead loop since here.
The dead loop is caught in the 32M hugetlb page (2M PMD + Contiguous bit).
This patch removes wrong pmd check, and fixes this dead loop.
This patch also removes the redundant checks for PGD/PUD in the find_num_contig().
Acked-by: Steve Capper <steve.capper@arm.com> Signed-off-by: Huang Shijie <shijie.huang@arm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/arm64/mm/hugetlbpage.c | 12 ------------ 1 file changed, 12 deletions(-)
--- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -51,20 +51,8 @@ static int find_num_contig(struct mm_str *pgsize = PAGE_SIZE; if (!pte_cont(pte)) return 1; - if (!pgd_present(*pgd)) { - VM_BUG_ON(!pgd_present(*pgd)); - return 1; - } pud = pud_offset(pgd, addr); - if (!pud_present(*pud)) { - VM_BUG_ON(!pud_present(*pud)); - return 1; - } pmd = pmd_offset(pud, addr); - if (!pmd_present(*pmd)) { - VM_BUG_ON(!pmd_present(*pmd)); - return 1; - } if ((pte_t *)pmd == ptep) { *pgsize = PMD_SIZE; return CONT_PMDS;
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