vm: object: ensure page request offets are page-aligned

vm/vm-object.c

@@ -392,6 +392,7 @@ struct vm_page *vm_object_get_page(
 	enum vm_object_flags flags,
 	unsigned long *irq_flags)
 {
+	offset &= ~VM_PAGE_MASK;
 	if (!vo->vo_ctrl && (flags & VMO_ALLOCATE_MISSING_PAGE)) {
 		return alloc_page(vo, offset);
 	}