Anshuman Khandual <khand...@linux.vnet.ibm.com> writes:
> On 02/18/2016 10:14 PM, Aneesh Kumar K.V wrote:
>> We can get a hash pte fault with 4k base page size and find the pte
>> already inserted with 64K base page size. In that case we need to clear
>
> Can you please elaborate on this ? What are those situations when we
> have 64K base page size on the PTE but we had inserted HPTE with base
> page size as 4K ?
when we demote a segment.
>
>> the existing slot information from the old pte. Fix this correctly
>>
>> With THP, we also clear the slot information with respect to all
>> the 64K hash pte mapping that 16MB page. They are all invalid
>> now. This make sure we don't find the slot valid when we fault with
>> 4k base page size. Finding the slot valid should not result in any wrong
>> behavior because we do check again in hash page table for the validity.
>> But we can avoid that check completely.
>
> Makes sense.
>
>>
>> Fixes: a43c0eb8364c022 ("powerpc/mm: Convert 4k hash insert to C")
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
>> ---
>> arch/powerpc/mm/hash64_4k.c | 2 +-
>> arch/powerpc/mm/hash64_64k.c | 12 +++++++++---
>> arch/powerpc/mm/hugepage-hash64.c | 7 ++++++-
>> 3 files changed, 16 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/powerpc/mm/hash64_4k.c b/arch/powerpc/mm/hash64_4k.c
>> index e7c04542ba62..e3e76b929f33 100644
>> --- a/arch/powerpc/mm/hash64_4k.c
>> +++ b/arch/powerpc/mm/hash64_4k.c
>> @@ -106,7 +106,7 @@ repeat:
>> }
>> }
>> /*
>> - * Hypervisor failure. Restore old pmd and return -1
>> + * Hypervisor failure. Restore old pte and return -1
>
> This change is not relevant here. Should be a separate patch.
>
>> * similar to __hash_page_*
>> */
>> if (unlikely(slot == -2)) {
>> diff --git a/arch/powerpc/mm/hash64_64k.c b/arch/powerpc/mm/hash64_64k.c
>> index 0762c1e08c88..b3895720edb0 100644
>> --- a/arch/powerpc/mm/hash64_64k.c
>> +++ b/arch/powerpc/mm/hash64_64k.c
>> @@ -111,7 +111,13 @@ int __hash_page_4K(unsigned long ea, unsigned long
>> access, unsigned long vsid,
>> */
>> if (!(old_pte & _PAGE_COMBO)) {
>> flush_hash_page(vpn, rpte, MMU_PAGE_64K, ssize, flags);
>> - old_pte &= ~_PAGE_HASHPTE | _PAGE_F_GIX | _PAGE_F_SECOND;
>> + /*
>> + * clear the old slot details from the old and new pte.
>> + * On hash insert failure we use old pte value and we don't
>> + * want slot information there if we have a insert failure.
>> + */
>> + old_pte &= ~(_PAGE_HASHPTE | _PAGE_F_GIX | _PAGE_F_SECOND);
>> + new_pte &= ~(_PAGE_HASHPTE | _PAGE_F_GIX | _PAGE_F_SECOND);
>
> But why we need clear the bits on new_pte as well ?
we use new pte when updating the actual pte towards the end of that function.
>
>> goto htab_insert_hpte;
>> }
>> /*
>> @@ -182,7 +188,7 @@ repeat:
>> }
>> }
>> /*
>> - * Hypervisor failure. Restore old pmd and return -1
>> + * Hypervisor failure. Restore old pte and return -1
>
> This change is not relevant here. Should be a separate patch.
>
>
>> * similar to __hash_page_*
>> */
>> if (unlikely(slot == -2)) {
>> @@ -305,7 +311,7 @@ repeat:
>> }
>> }
>> /*
>> - * Hypervisor failure. Restore old pmd and return -1
>> + * Hypervisor failure. Restore old pte and return -1
>> * similar to __hash_page_*
>
> Ditto.
-anessh
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
