Christophe Leroy's on June 7, 2019 3:35 pm:
>
>
> Le 07/06/2019 à 05:56, Nicholas Piggin a écrit :
>> 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.
>>
>> 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
>> +
>
> Could get rid of that #ifdef by adding the following in book3s32 and
> nohash pgtable.h:
>
> static inline bool pmd_is_serializing() { return false; }
I don't mind either way. If it's an isolated case like this, sometimes
I'm against polluting the sub arch code with it.
It's up to you I can change that if you prefer.
Thanks,
Nick
