diff -r c4eead8a925b tools/libxc/xc_linux_build.c
--- a/tools/libxc/xc_linux_build.c	Sun Apr 16 14:41:31 2006
+++ b/tools/libxc/xc_linux_build.c	Thu Apr 20 22:45:21 2006
@@ -45,6 +45,11 @@
 #ifdef __ia64__
 #define probe_aout9(image,image_size,load_funcs) 1
 #endif
+
+/* from xc_ptrace.h */
+#define X86_CR0_PE              0x00000001 /* Enable Protected Mode    (RW) */
+#define X86_CR0_PG              0x80000000 /* Paging                   (RW) */
+
 
 struct initrd_info {
     enum { INITRD_none, INITRD_file, INITRD_mem } type;
@@ -1174,6 +1179,8 @@
     ctxt->failsafe_callback_eip = 0;
     ctxt->syscall_callback_eip  = 0;
 #endif
+    /* set sane cr0 bits, protected and paging enabled  */
+    ctxt->ctrlreg[0] = X86_CR0_PE|X86_CR0_PG;
 #endif /* x86 */
 
     memset( &launch_op, 0, sizeof(launch_op) );
diff -r c4eead8a925b linux-2.6-xen-sparse/drivers/xen/core/smpboot.c
--- a/linux-2.6-xen-sparse/drivers/xen/core/smpboot.c	Sun Apr 16 14:41:31 2006
+++ b/linux-2.6-xen-sparse/drivers/xen/core/smpboot.c	Thu Apr 20 22:45:36 2006
@@ -216,6 +216,8 @@
 
 	ctxt.gs_base_kernel = (unsigned long)(cpu_pda(vcpu));
 #endif
+   /* set sane cr0 bits, protected and paging enabled  */
+   ctxt.ctrlreg[0] = 0x80000001;
 
 	BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_initialise, vcpu, &ctxt));
 }