KVM: Simply gfn_to_page()

Mapping a guest page to a host page is a common operation.  Currently,
one has first to find the memory slot where the page belongs (gfn_to_memslot),
then locate the page itself (gfn_to_page()).

This is clumsy, and also won't work well with memory aliases.  So simplify
gfn_to_page() not to require memory slot translation first, and instead do it
internally.

Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index b64b7b7..61a6116 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -926,9 +926,9 @@
 	gfn_t fn = rmode_tss_base(kvm) >> PAGE_SHIFT;
 	char *page;
 
-	p1 = _gfn_to_page(kvm, fn++);
-	p2 = _gfn_to_page(kvm, fn++);
-	p3 = _gfn_to_page(kvm, fn);
+	p1 = gfn_to_page(kvm, fn++);
+	p2 = gfn_to_page(kvm, fn++);
+	p3 = gfn_to_page(kvm, fn);
 
 	if (!p1 || !p2 || !p3) {
 		kvm_printf(kvm,"%s: gfn_to_page failed\n", __FUNCTION__);