mirror of https://gitee.com/openkylin/linux.git
arm64: hugetlb: remove the wrong pmd check in find_num_contig()
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>
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@ -51,20 +51,8 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
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*pgsize = PAGE_SIZE;
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if (!pte_cont(pte))
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return 1;
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if (!pgd_present(*pgd)) {
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VM_BUG_ON(!pgd_present(*pgd));
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return 1;
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}
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pud = pud_offset(pgd, addr);
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if (!pud_present(*pud)) {
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VM_BUG_ON(!pud_present(*pud));
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return 1;
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}
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pmd = pmd_offset(pud, addr);
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if (!pmd_present(*pmd)) {
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VM_BUG_ON(!pmd_present(*pmd));
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return 1;
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}
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if ((pte_t *)pmd == ptep) {
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*pgsize = PMD_SIZE;
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return CONT_PMDS;
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