From f049a4f7ffa50000485a61d5518ffae24b662aaa Mon Sep 17 00:00:00 2001
From: Heiko Carstens <hca@linux.ibm.com>
Date: Wed, 30 Apr 2025 10:59:30 +0200
Subject: [PATCH] s390/mm: Add mmap_assert_write_locked() check to
crst_table_upgrade()
Add mmap_assert_write_locked() check to crst_table_upgrade() in order to
verify that no concurrent page table upgrades of an mm can happen. This
allows to remove the VM_BUG_ON() check which checks for the potential
inconsistent result of concurrent updates.
Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/mm/pgalloc.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 9470280831d8..e33903b419a9 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -56,6 +56,8 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
unsigned long *pgd = NULL, *p4d = NULL, *__pgd;
unsigned long asce_limit = mm->context.asce_limit;
+ mmap_assert_write_locked(mm);
+
/* upgrade should only happen from 3 to 4, 3 to 5, or 4 to 5 levels */
VM_BUG_ON(asce_limit < _REGION2_SIZE);
@@ -79,13 +81,6 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
spin_lock_bh(&mm->page_table_lock);
- /*
- * This routine gets called with mmap_lock lock held and there is
- * no reason to optimize for the case of otherwise. However, if
- * that would ever change, the below check will let us know.
- */
- VM_BUG_ON(asce_limit != mm->context.asce_limit);
-
if (p4d) {
__pgd = (unsigned long *) mm->pgd;
p4d_populate(mm, (p4d_t *) p4d, (pud_t *) __pgd);