mm/ksm: move disabling KSM from s390/gmap code to KSM code

Let's factor out actual disabling of KSM.  The existing "mm->def_flags &=
~VM_MERGEABLE;" was essentially a NOP and can be dropped, because
def_flags should never include VM_MERGEABLE.  Note that we don't currently
prevent re-enabling KSM.

This should now be faster in case KSM was never enabled, because we only
conditionally iterate all VMAs.  Further, it certainly looks cleaner.

Link: https://lkml.kernel.org/r/20230422210156.33630-1-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Acked-by: Stefan Roesch <shr@devkernel.io>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/s390/mm/gmap.c

@@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
 
 int gmap_mark_unmergeable(void)
 {
-	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
-	unsigned long vm_flags;
-	int ret;
-	VMA_ITERATOR(vmi, mm, 0);
-
 	/*
 	 * Make sure to disable KSM (if enabled for the whole process or
 	 * individual VMAs). Note that nothing currently hinders user space
 	 * from re-enabling it.
 	 */
-	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
-
-	for_each_vma(vmi, vma) {
-		/* Copy vm_flags to avoid partial modifications in ksm_madvise */
-		vm_flags = vma->vm_flags;
-		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-				  MADV_UNMERGEABLE, &vm_flags);
-		if (ret)
-			return ret;
-		vm_flags_reset(vma, vm_flags);
-	}
-	mm->def_flags &= ~VM_MERGEABLE;
-	return 0;
+	return ksm_disable(current->mm);
 }
 EXPORT_SYMBOL_GPL(gmap_mark_unmergeable);
 

include/linux/ksm.h

@@ -22,6 +22,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 void ksm_add_vma(struct vm_area_struct *vma);
 int ksm_enable_merge_any(struct mm_struct *mm);
 int ksm_disable_merge_any(struct mm_struct *mm);
+int ksm_disable(struct mm_struct *mm);
 
 int __ksm_enter(struct mm_struct *mm);
 void __ksm_exit(struct mm_struct *mm);
@@ -80,6 +81,11 @@ static inline void ksm_add_vma(struct vm_area_struct *vma)
 {
 }
 
+static inline int ksm_disable(struct mm_struct *mm)
+{
+	return 0;
+}
+
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
 	return 0;

mm/ksm.c

@@ -2628,6 +2628,17 @@ int ksm_disable_merge_any(struct mm_struct *mm)
 	return 0;
 }
 
+int ksm_disable(struct mm_struct *mm)
+{
+	mmap_assert_write_locked(mm);
+
+	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
+		return 0;
+	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+		return ksm_disable_merge_any(mm);
+	return ksm_del_vmas(mm);
+}
+
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 		unsigned long end, int advice, unsigned long *vm_flags)
 {