[PATCH] powerpc: IOMMU: don't ioremap null addresses

240-ioremap-null-ptr-test.patch

Under highly unusual circumstances, a buggy driver will ask a null ptr
to be ioremapped, an operation that curently succeeds but leads to
later trouble.  Instead, refuse to remap the null pointer.
Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
(cherry picked from e71d9e598533c1889e7162f5f4647e5d378c102c commit)

arch/powerpc/mm/pgtable_64.c

@@ -174,7 +174,7 @@ void __iomem * __ioremap(unsigned long addr, unsigned long size,
 	pa = addr & PAGE_MASK;
 	size = PAGE_ALIGN(addr + size) - pa;
 
-	if (size == 0)
+	if ((size == 0) || (pa == 0))
 		return NULL;
 
 	if (mem_init_done) {