get_user_pages: don't try to follow PFNMAP pages

Nick Piggin points out that a few drivers play games with VM_IO (why?
who knows..) and thus a pfn-remapped area may not have that bit set even
if remap_pfn_range() set it originally.

So make it explicit in get_user_pages() that we don't follow VM_PFNMAP
pages, since pretty much by definition they do not have a "struct page"
associated with them.
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/memory.c

@@ -1009,7 +1009,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 			continue;
 		}
 
-		if (!vma || (vma->vm_flags & VM_IO)
+		if (!vma || (vma->vm_flags & (VM_IO | VM_PFNMAP))
 				|| !(vm_flags & vma->vm_flags))
 			return i ? : -EFAULT;