x86/apic: Annotate global config variables as "read-only after init"

Mark the APIC's global config variables that are constant after boot as
__ro_after_init to help document that the majority of the APIC config is
not changed at runtime, and to harden the kernel a smidge.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190805212134.12001-1-sean.j.christopherson@intel.com

arch/x86/kernel/apic/apic.c

@@ -65,10 +65,10 @@ unsigned int num_processors;
 unsigned disabled_cpus;
 
 /* Processor that is doing the boot up */
-unsigned int boot_cpu_physical_apicid = -1U;
+unsigned int boot_cpu_physical_apicid __ro_after_init = -1U;
 EXPORT_SYMBOL_GPL(boot_cpu_physical_apicid);
 
-u8 boot_cpu_apic_version;
+u8 boot_cpu_apic_version __ro_after_init;
 
 /*
  * The highest APIC ID seen during enumeration.
@@ -85,13 +85,13 @@ physid_mask_t phys_cpu_present_map;
  * disable_cpu_apicid=<int>, mostly used for the kdump 2nd kernel to
  * avoid undefined behaviour caused by sending INIT from AP to BSP.
  */
-static unsigned int disabled_cpu_apicid __read_mostly = BAD_APICID;
+static unsigned int disabled_cpu_apicid __ro_after_init = BAD_APICID;
 
 /*
  * This variable controls which CPUs receive external NMIs.  By default,
  * external NMIs are delivered only to the BSP.
  */
-static int apic_extnmi = APIC_EXTNMI_BSP;
+static int apic_extnmi __ro_after_init = APIC_EXTNMI_BSP;
 
 /*
  * Map cpu index to physical APIC ID
@@ -114,7 +114,7 @@ EXPORT_EARLY_PER_CPU_SYMBOL(x86_cpu_to_acpiid);
 DEFINE_EARLY_PER_CPU_READ_MOSTLY(int, x86_cpu_to_logical_apicid, BAD_APICID);
 
 /* Local APIC was disabled by the BIOS and enabled by the kernel */
-static int enabled_via_apicbase;
+static int enabled_via_apicbase __ro_after_init;
 
 /*
  * Handle interrupt mode configuration register (IMCR).
@@ -172,23 +172,23 @@ static __init int setup_apicpmtimer(char *s)
 __setup("apicpmtimer", setup_apicpmtimer);
 #endif
 
-unsigned long mp_lapic_addr;
-int disable_apic;
+unsigned long mp_lapic_addr __ro_after_init;
+int disable_apic __ro_after_init;
 /* Disable local APIC timer from the kernel commandline or via dmi quirk */
 static int disable_apic_timer __initdata;
 /* Local APIC timer works in C2 */
-int local_apic_timer_c2_ok;
+int local_apic_timer_c2_ok __ro_after_init;
 EXPORT_SYMBOL_GPL(local_apic_timer_c2_ok);
 
 /*
  * Debug level, exported for io_apic.c
  */
-int apic_verbosity;
+int apic_verbosity __ro_after_init;
 
-int pic_mode;
+int pic_mode __ro_after_init;
 
 /* Have we found an MP table */
-int smp_found_config;
+int smp_found_config __ro_after_init;
 
 static struct resource lapic_resource = {
 	.name = "Local APIC",
@@ -199,7 +199,7 @@ unsigned int lapic_timer_period = 0;
 
 static void apic_pm_activate(void);
 
-static unsigned long apic_phys;
+static unsigned long apic_phys __ro_after_init;
 
 /*
  * Get the LAPIC version
@@ -1278,7 +1278,7 @@ void __init sync_Arb_IDs(void)
 			APIC_INT_LEVELTRIG | APIC_DM_INIT);
 }
 
-enum apic_intr_mode_id apic_intr_mode;
+enum apic_intr_mode_id apic_intr_mode __ro_after_init;
 
 static int __init apic_intr_mode_select(void)
 {