HV: enable SMEP in hypervisor

- this patch is to enable SMEP in hypervisor, SMEP protects
   guests' memory from supervisor-mode instruction fetches,
   in other words, hypervisor which operating in supervisor
   mode can't fetch instructions from (guests' memory)
   linear addresses that are accessible in user mode.

Signed-off-by: Yonghua Huang <yonghua.huang@intel.com>

hypervisor/arch/x86/cpu.c

@@ -495,6 +495,8 @@ void bsp_boot_init(void)
 		pr_fatal("Please apply the latest CPU uCode patch!");
 	}
 
+	enable_smep();
+
 	/* Initialize the shell */
 	shell_init();
 
@@ -546,6 +548,9 @@ void cpu_secondary_init(void)
 	 * primary/boot CPU
 	 */
 	enable_paging(get_paging_pml4());
+
+	enable_smep();
+
 	early_init_lapic();
 
 	/* Find the logical ID of this CPU given the LAPIC ID