s390/mm: Check for valid vma before zapping in gmap_discard

From: Janosch Frank <[email protected]>

Userspace could have munmapped the area before doing unmapping from the gmap. This would leave us with a valid vmaddr, but an invalid vma from which we would try to zap memory. Let's check before using the vma.

Function was moved with 1e133ab296f3 in v4.6.
Is 1843abd upstream.

---
 arch/s390/mm/pgtable.c | 2 ++
 1 file changed, 2 insertions(+)

index 05ae254..1866b6a 100644
@@ -637,6 +637,8 @@ void gmap_discard(struct gmap *gmap, unsigned long from, unsigned long to)
 		vmaddr |= gaddr & ~PMD_MASK;
 		/* Find vma in the parent mm */
 		vma = find_vma(gmap->mm, vmaddr);
+		if (!vma)
+			continue;
 		size = min(to - gaddr, PMD_SIZE - (gaddr & ~PMD_MASK));
 		zap_page_range(vma, vmaddr, size, NULL);
 	}

2.7.4