Commit ec4abf1e authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Michael Ellerman
Browse files

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



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: default avatarAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200505071729.54912-4-aneesh.kumar@linux.ibm.com
parent c46241a3

arch/powerpc/include/asm/book3s/64/pgtable.h

+10 −5
Original line number Diff line number Diff line
@@ -553,6 +553,12 @@ static inline pte_t pte_clear_savedwrite(pte_t pte) 
}

#endif /* CONFIG_NUMA_BALANCING */



static inline bool pte_hw_valid(pte_t pte)

{

	return (pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE)) ==

		cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE);

}



static inline int pte_present(pte_t pte)

{

	/*
@@ -561,12 +567,11 @@ static inline int pte_present(pte_t pte) 
	 * invalid during ptep_set_access_flags. Hence we look for _PAGE_INVALID

	 * if we find _PAGE_PRESENT cleared.

	 */

	return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_INVALID));

}



static inline bool pte_hw_valid(pte_t pte)

{

	return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT));

	if (pte_hw_valid(pte))

		return true;

	return (pte_raw(pte) & cpu_to_be64(_PAGE_INVALID | _PAGE_PTE)) ==

		cpu_to_be64(_PAGE_INVALID | _PAGE_PTE);

}



#ifdef CONFIG_PPC_MEM_KEYS

arch/powerpc/mm/book3s64/hash_utils.c

+9 −2
Original line number Diff line number Diff line
@@ -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

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