On 14.09.21 18:54, Claudio Imbrenda wrote:

On Thu,  9 Sep 2021 18:22:46 +0200
David Hildenbrand [off-list ref] wrote:

quoted

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."

quoted

Signed-off-by: David Hildenbrand <redacted>
---
  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