s390/mm: optimize set_guest_storage_key()

We already optimize get_guest_storage_key() to assume that if we don't have
a PTE table and don't have a huge page mapped that the storage key is 0.

Similarly, optimize set_guest_storage_key() to simply do nothing in case
the key to set is 0.

Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20210909162248.14969-9-david@redhat.com
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index e74cc59dcd67d8b18be0f3b2fb58f9e3b2a676db..1c9aeb361f8dcddf9ecbc3c94153e97973ba6f55 100644 (file)
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -792,13 +792,23 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
        pmd_t *pmdp;
        pte_t *ptep;
 
-       if (pmd_lookup(mm, addr, &pmdp))
+       /*
+        * If we don't have a PTE table and if there is no huge page mapped,
+        * we can ignore attempts to set the key to 0, because it already is 0.
+        */
+       switch (pmd_lookup(mm, addr, &pmdp)) {
+       case -ENOENT:
+               return key ? -EFAULT : 0;
+       case 0:
+               break;
+       default:
                return -EFAULT;
+       }
 
        ptl = pmd_lock(mm, pmdp);
        if (!pmd_present(*pmdp)) {
                spin_unlock(ptl);
-               return -EFAULT;
+               return key ? -EFAULT : 0;
        }
 
        if (pmd_large(*pmdp)) {