perf/x86: Add __ro_after_init annotations

x86_pmu_{format,events,attr,caps}_group is written to in
init_hw_perf_events and not modified after. This makes them suitable
candidates for annotating as __ro_after_init.

Signed-off-by: Zubin Mithra <zsm@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@kernel.org
Cc: alexander.shishkin@linux.intel.com
Cc: groeck@chromium.org
Link: http://lkml.kernel.org/r/20180810154314.96710-1-zsm@chromium.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/core.c

@@ -1584,7 +1584,7 @@ static void __init pmu_check_apic(void)
 
 }
 
-static struct attribute_group x86_pmu_format_group = {
+static struct attribute_group x86_pmu_format_group __ro_after_init = {
 	.name = "format",
 	.attrs = NULL,
 };
@@ -1715,7 +1715,7 @@ static struct attribute *events_attr[] = {
 	NULL,
 };
 
-static struct attribute_group x86_pmu_events_group = {
+static struct attribute_group x86_pmu_events_group __ro_after_init = {
 	.name = "events",
 	.attrs = events_attr,
 };
@@ -2230,7 +2230,7 @@ static struct attribute *x86_pmu_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group x86_pmu_attr_group = {
+static struct attribute_group x86_pmu_attr_group __ro_after_init = {
 	.attrs = x86_pmu_attrs,
 };
 
@@ -2248,7 +2248,7 @@ static struct attribute *x86_pmu_caps_attrs[] = {
 	NULL
 };
 
-static struct attribute_group x86_pmu_caps_group = {
+static struct attribute_group x86_pmu_caps_group __ro_after_init = {
 	.name = "caps",
 	.attrs = x86_pmu_caps_attrs,
 };