arm64: arch_timer: Disable CNTVCT_EL0 trap if workaround is enabled

hulk inclusion
category: performance
bugzilla: 16082
CVE: NA

-------------------------------------------------

It costs very much time to read CNTVCT_EL0, if a cntvct workaround
and CNTVCT_EL0 trap is enabled. To decrease the read time, we disable
CNTVCT_EL0 trap and do the cntvct workaround in the VDSO by adding
vdso_fix.
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Reviewed-by: NXuefeng Wang <wxf.wang@hisilicon.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/clocksource/arm_arch_timer.c

@@ -76,6 +76,7 @@ static bool arch_timer_c3stop;
 static bool arch_timer_mem_use_virtual;
 static bool arch_counter_suspend_stop;
 static bool vdso_default = true;
+DEFINE_STATIC_KEY_FALSE(vdso_fix);
 
 static cpumask_t evtstrm_available = CPU_MASK_NONE;
 static bool evtstrm_enable = IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM);
@@ -550,8 +551,9 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
 	 * change both the default value and the vdso itself.
 	 */
 	if (wa->read_cntvct_el0) {
-		clocksource_counter.archdata.vdso_direct = false;
-		vdso_default = false;
+		clocksource_counter.archdata.vdso_direct = true;
+		vdso_default = true;
+		static_branch_enable(&vdso_fix);
 	}
 }
 
@@ -855,7 +857,8 @@ static void arch_counter_set_user_access(void)
 	 * need to be workaround. The vdso may have been already
 	 * disabled though.
 	 */
-	if (arch_timer_this_cpu_has_cntvct_wa())
+	if (arch_timer_this_cpu_has_cntvct_wa() &&
+	    !static_branch_unlikely(&vdso_fix))
 		pr_info("CPU%d: Trapping CNTVCT access\n", smp_processor_id());
 	else
 		cntkctl |= ARCH_TIMER_USR_VCT_ACCESS_EN;