Re: [PATCH resend RFC 7/9] s390/mm: no need for pte_alloc_map_lock() if we know the pmd is present

David Hildenbrand
2021-09-14T17:23:42Z

On 14.09.21 18:54, Claudio Imbrenda wrote:
> On Thu, 9 Sep 2021 18:22:46 +0200
> David Hildenbrand <david@redhat.com> wrote:
>
>> pte_map_lock() is sufficient.
>
> Can you explain the difference and why it is enough?

I didn't repeat the $subject:

"No need for pte_alloc_map_lock() if we know the pmd is present;
pte_map_lock() is sufficient, because there isn't anything to allocate."

>
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>> arch/s390/mm/pgtable.c | 15 +++------------
>> 1 file changed, 3 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
>> index 5fb409ff7842..4e77b8ebdcc5 100644
>> --- a/arch/s390/mm/pgtable.c
>> +++ b/arch/s390/mm/pgtable.c
>> @@ -814,10 +814,7 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
>> }
>> spin_unlock(ptl);
>>
>> - ptep = pte_alloc_map_lock(mm, pmdp, addr, &ptl);
>> - if (unlikely(!ptep))
>> - return -EFAULT;
>> -
>> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
>> new = old = pgste_get_lock(ptep);
>> pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT |
>> PGSTE_ACC_BITS | PGSTE_FP_BIT);
>> @@ -912,10 +909,7 @@ int reset_guest_reference_bit(struct mm_struct *mm, unsigned long addr)
>> }
>> spin_unlock(ptl);
>>
>> - ptep = pte_alloc_map_lock(mm, pmdp, addr, &ptl);
>> - if (unlikely(!ptep))
>> - return -EFAULT;
>> -
>> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
>> new = old = pgste_get_lock(ptep);
>> /* Reset guest reference bit only */
>> pgste_val(new) &= ~PGSTE_GR_BIT;
>> @@ -977,10 +971,7 @@ int get_guest_storage_key(struct mm_struct *mm, unsigned long addr,
>> }
>> spin_unlock(ptl);
>>
>> - ptep = pte_alloc_map_lock(mm, pmdp, addr, &ptl);
>> - if (unlikely(!ptep))
>> - return -EFAULT;
>> -
>> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
>> pgste = pgste_get_lock(ptep);
>> *key = (pgste_val(pgste) & (PGSTE_ACC_BITS | PGSTE_FP_BIT)) >> 56;
>> paddr = pte_val(*ptep) & PAGE_MASK;
>

--
Thanks,

David / dhildenb