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powerpc/mm/hash64: use _PAGE_PTE when checking for pte_present

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This makes the pte_present check stricter by checking for additional _PAGE_PTE
bit. A level 1 pte pointer (THP pte) can be switched to a pointer to level 0 pte
page table page by following two operations.

1) THP split.
2) madvise(MADV_DONTNEED) in parallel to page fault.

A lockless page table walk need to make sure we can handle such changes
gracefully.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200505071729.54912-4-aneesh.kumar@linux.ibm.com
This commit is contained in:
Aneesh Kumar K.V
2020-05-05 12:47:10 +05:30
committed by Michael Ellerman
parent c46241a370
commit ec4abf1e70
2 changed files with 19 additions and 7 deletions
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11
arch/powerpc/mm/book3s64/hash_utils.c
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@@ -1350,8 +1350,15 @@ int hash_page_mm(struct mm_struct *mm, unsigned long ea,
goto bail;
}
/* Add _PAGE_PRESENT to the required access perm */
access |= _PAGE_PRESENT;
/*
* Add _PAGE_PRESENT to the required access perm. If there are parallel
* updates to the pte that can possibly clear _PAGE_PTE, catch that too.
*
* We can safely use the return pte address in rest of the function
* because we do set H_PAGE_BUSY which prevents further updates to pte
* from generic code.
*/
access |= _PAGE_PRESENT | _PAGE_PTE;
/*
* Pre-check access permissions (will be re-checked atomically