KVM: s390/mm: Fix page table locking vs. split pmd lock

commit ec66ad66a0de87866be347b5ecc83bd46427f53b (s390/mm: enable
split page table lock for PMD level) activated the split pmd lock
for s390. Turns out that we missed one place: We also have to take
the pmd lock instead of the page table lock when we reallocate the
page tables (==> changing entries in the PMD) during sie enablement.

Cc: stable@vger.kernel.org # 3.15+
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 37b8241ec784..f90ad8592b36 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -1279,6 +1279,7 @@ static unsigned long page_table_realloc_pmd(struct mmu_gather *tlb,
 {
         unsigned long next, *table, *new;
         struct page *page;
+        spinlock_t *ptl;
         pmd_t *pmd;
 
         pmd = pmd_offset(pud, addr);
@@ -1296,7 +1297,7 @@ again:
                 if (!new)
                         return -ENOMEM;
 
-                spin_lock(&mm->page_table_lock);
+                ptl = pmd_lock(mm, pmd);
                 if (likely((unsigned long *) pmd_deref(*pmd) == table)) {
                         /* Nuke pmd entry pointing to the "short" page table */
                         pmdp_flush_lazy(mm, addr, pmd);
@@ -1310,7 +1311,7 @@ again:
                         page_table_free_rcu(tlb, table);
                         new = NULL;
                 }
-                spin_unlock(&mm->page_table_lock);
+                spin_unlock(ptl);
                 if (new) {
                         page_table_free_pgste(new);
                         goto again;