KVM: PPC: cache flush for kernel managed pages

Kernel can only access pages which maps as memory.
So flush only the valid kernel pages.
Signed-off-by: NBharat Bhushan <bharat.bhushan@freescale.com>
Signed-off-by: NAlexander Graf <agraf@suse.de>

arch/powerpc/include/asm/kvm_ppc.h

@@ -282,8 +282,15 @@ void kvmppc_init_lpid(unsigned long nr_lpids);
 
 static inline void kvmppc_mmu_flush_icache(pfn_t pfn)
 {
-	/* Clear i-cache for new pages */
 	struct page *page;
+	/*
+	 * We can only access pages that the kernel maps
+	 * as memory. Bail out for unmapped ones.
+	 */
+	if (!pfn_valid(pfn))
+		return;
+
+	/* Clear i-cache for new pages */
 	page = pfn_to_page(pfn);
 	if (!test_bit(PG_arch_1, &page->flags)) {
 		flush_dcache_icache_page(page);