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.cap...@arm.com>
Signed-off-by: Huang Shijie <shijie.hu...@arm.com>
---
arch/arm64/mm/hugetlbpage.c | 12 ------------
1 file changed, 12 deletions(-)
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 2e49bd2..b0d3f8b 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -51,20 +51,8 @@ static int find_num_contig(struct mm_struct *mm, unsigned
long addr,
*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;
--
2.5.5
