[S390] take mmap_sem when walking guest page table

gmap_fault needs to walk the guest page table. However, parts of
that may change if some other thread does munmap. In that case
gmap_unmap_notifier will also unmap the corresponding parts from
the guest page table. We need to take mmap_sem in order to serialize
these operations.
do_exception now calls __gmap_fault with mmap_sem held which does
not get exported to modules. The exported function, which is called
from KVM, now takes mmap_sem.

Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 96e85ac..441d344 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -393,7 +393,10 @@ out_unmap:
 }
 EXPORT_SYMBOL_GPL(gmap_map_segment);
 
-unsigned long gmap_fault(unsigned long address, struct gmap *gmap)
+/*
+ * this function is assumed to be called with mmap_sem held
+ */
+unsigned long __gmap_fault(unsigned long address, struct gmap *gmap)
 {
 	unsigned long *table, vmaddr, segment;
 	struct mm_struct *mm;
@@ -461,7 +464,17 @@ unsigned long gmap_fault(unsigned long address, struct gmap *gmap)
 		return vmaddr | (address & ~PMD_MASK);
 	}
 	return -EFAULT;
+}
+
+unsigned long gmap_fault(unsigned long address, struct gmap *gmap)
+{
+	unsigned long rc;
+
+	down_read(&gmap->mm->mmap_sem);
+	rc = __gmap_fault(address, gmap);
+	up_read(&gmap->mm->mmap_sem);
 
+	return rc;
 }
 EXPORT_SYMBOL_GPL(gmap_fault);