Commits
Huang Shijie committed 2021e55d719
arm64: hugetlb: remove the wrong pmd check in find_num_contig()
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>