Index: /trunk/src/VBox/HostDrivers/Support/linux/SUPDrv-linux.c
===================================================================
--- /trunk/src/VBox/HostDrivers/Support/linux/SUPDrv-linux.c	(revision 259)
+++ /trunk/src/VBox/HostDrivers/Support/linux/SUPDrv-linux.c	(revision 260)
@@ -55,6 +55,10 @@
 #endif
 
-#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 0) && !defined(page_to_pfn)
-# define page_to_pfn(page) ((page) - mem_map)
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 0)
+# ifndef page_to_pfn
+#  define page_to_pfn(page) ((page) - mem_map)
+# endif
+# include <asm/pgtable.h>
+# define global_flush_tlb __flush_tlb_global
 #endif
 
Index: /trunk/src/VBox/Runtime/r0drv/linux/the-linux-kernel.h
===================================================================
--- /trunk/src/VBox/Runtime/r0drv/linux/the-linux-kernel.h	(revision 259)
+++ /trunk/src/VBox/Runtime/r0drv/linux/the-linux-kernel.h	(revision 260)
@@ -33,4 +33,13 @@
 #include <linux/autoconf.h>
 #include <linux/version.h>
+
+/* We only support 2.4 and 2.6 series kernels */
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 4, 0)
+# error We only support 2.4 and 2.6 series kernels
+#endif
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 5, 0) && LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 0)
+# error We only support 2.4 and 2.6 series kernels
+#endif
+
 #if defined(CONFIG_MODVERSIONS) && !defined(MODVERSIONS)
 # define MODVERSIONS