[PATCH] ppc64: Fix the lazy icache/dcache code for non-RAM pages

For some stupid reason I can't explain (brown paper bag is at hand), I
removed the check pfn_valid() in the code that does the icache/dcache
coherency on POWER4 and later. That causes us to eventually try to
access non existing struct page when hashing in IO pages.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 3d83c3b..22e4748 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -507,6 +507,9 @@
 {
 	struct page *page;
 
+	if (!pfn_valid(pte_pfn(pte)))
+		return pp;
+
 	page = pte_page(pte);
 
 	/* page is dirty */