From: Janosch Frank <frankja@linux.ibm.com>
Subject: s390/mm: Check for valid vma before zapping in gmap_discard
Patch-mainline: v4.19-rc5
Git-commit: 1843abd03250115af6cec0892683e70cf2297c25
References: FATE#326372, LTC#169184, bsc#1113484

Summary:     kernel: Introduce huge page KVM backing support
Description: This adds the KVM support for libhugetlbfs backings of
             s390 KVM guests.

Upstream-Description:

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

             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.

             Fixes: 1e133ab296f3 ("s390/mm: split arch/s390/mm/pgtable.c")
             Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
             Reviewed-by: David Hildenbrand <david@redhat.com>
             Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
             Message-Id: <20180816082432.78828-1-frankja@linux.ibm.com>
             Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 arch/s390/mm/gmap.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -704,11 +704,13 @@ void gmap_discard(struct gmap *gmap, uns
 		vmaddr |= gaddr & ~PMD_MASK;
 		/* Find vma in the parent mm */
 		vma = find_vma(gmap->mm, vmaddr);
+		if (!vma)
+			continue;
 		/*
 		 * We do not discard pages that are backed by
 		 * hugetlbfs, so we don't have to refault them.
 		 */
-		if (vma && is_vm_hugetlb_page(vma))
+		if (is_vm_hugetlb_page(vma))
 			continue;
 		size = min(to - gaddr, PMD_SIZE - (gaddr & ~PMD_MASK));
 		zap_page_range(vma, vmaddr, size);