[PATCH resend RFC 9/9] s390/mm: optimize reset_guest_reference_bit()

David Hildenbrand
2021-09-09T16:24:10Z

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 reset_guest_reference_bit() to simply do nothing if
there is no PTE table and no huge page mapped.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/s390/mm/pgtable.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 534939a3eca5..50ab2fed3397 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -901,13 +901,23 @@ int reset_guest_reference_bit(struct mm_struct *mm, unsigned long addr)
pte_t *ptep;
int cc = 0;

- if (pmd_lookup(mm, addr, &pmdp))
+ /*
+ * If we don't have a PTE table and if there is no huge page mapped,
+ * the storage key is 0 and there is nothing for us to do.
+ */
+ switch (pmd_lookup(mm, addr, &pmdp)) {
+ case -ENOENT:
+ return 0;
+ case 0:
+ break;
+ default:
return -EFAULT;
+ }

ptl = pmd_lock(mm, pmdp);
if (!pmd_present(*pmdp)) {
spin_unlock(ptl);
- return -EFAULT;
+ return 0;
}

if (pmd_large(*pmdp)) {
--
2.31.1