Nicholas Piggin <npig...@gmail.com> writes:
> The change to pmdp_invalidate to mark the pmd with _PAGE_INVALID broke
> the synchronisation against lock free lookups, __find_linux_pte's
> pmd_none check no longer returns true for such cases.
>
> Fix this by adding a check for this condition as well.
>
Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
> Fixes: da7ad366b497 ("powerpc/mm/book3s: Update pmd_present to look at
> _PAGE_PRESENT bit")
> Cc: Christophe Leroy <christophe.le...@c-s.fr>
> Suggested-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
> ---
> arch/powerpc/mm/pgtable.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index db4a6253df92..533fc6fa6726 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -372,13 +372,25 @@ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea,
> pdshift = PMD_SHIFT;
> pmdp = pmd_offset(&pud, ea);
> pmd = READ_ONCE(*pmdp);
> +
> /*
> - * A hugepage collapse is captured by pmd_none, because
> - * it mark the pmd none and do a hpte invalidate.
> + * A hugepage collapse is captured by this condition, see
> + * pmdp_collapse_flush.
> */
> if (pmd_none(pmd))
> return NULL;
>
> +#ifdef CONFIG_PPC_BOOK3S_64
> + /*
> + * A hugepage split is captured by this condition, see
> + * pmdp_invalidate.
> + *
> + * Huge page modification can be caught here too.
> + */
> + if (pmd_is_serializing(pmd))
> + return NULL;
> +#endif
> +
> if (pmd_trans_huge(pmd) || pmd_devmap(pmd)) {
> if (is_thp)
> *is_thp = true;
> --
> 2.20.1
