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Diffstat (limited to 'arch/x86/kernel/cpu/umwait.c')
-rw-r--r--arch/x86/kernel/cpu/umwait.c39
1 files changed, 38 insertions, 1 deletions
diff --git a/arch/x86/kernel/cpu/umwait.c b/arch/x86/kernel/cpu/umwait.c
index 6a204e7336c1..32b4dc9030aa 100644
--- a/arch/x86/kernel/cpu/umwait.c
+++ b/arch/x86/kernel/cpu/umwait.c
@@ -18,6 +18,12 @@
static u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000, UMWAIT_C02_ENABLE);
/*
+ * Cache the original IA32_UMWAIT_CONTROL MSR value which is configured by
+ * hardware or BIOS before kernel boot.
+ */
+static u32 orig_umwait_control_cached __ro_after_init;
+
+/*
* Serialize access to umwait_control_cached and IA32_UMWAIT_CONTROL MSR in
* the sysfs write functions.
*/
@@ -53,6 +59,23 @@ static int umwait_cpu_online(unsigned int cpu)
}
/*
+ * The CPU hotplug callback sets the control MSR to the original control
+ * value.
+ */
+static int umwait_cpu_offline(unsigned int cpu)
+{
+ /*
+ * This code is protected by the CPU hotplug already and
+ * orig_umwait_control_cached is never changed after it caches
+ * the original control MSR value in umwait_init(). So there
+ * is no race condition here.
+ */
+ wrmsr(MSR_IA32_UMWAIT_CONTROL, orig_umwait_control_cached, 0);
+
+ return 0;
+}
+
+/*
* On resume, restore IA32_UMWAIT_CONTROL MSR on the boot processor which
* is the only active CPU at this time. The MSR is set up on the APs via the
* CPU hotplug callback.
@@ -185,8 +208,22 @@ static int __init umwait_init(void)
if (!boot_cpu_has(X86_FEATURE_WAITPKG))
return -ENODEV;
+ /*
+ * Cache the original control MSR value before the control MSR is
+ * changed. This is the only place where orig_umwait_control_cached
+ * is modified.
+ */
+ rdmsrl(MSR_IA32_UMWAIT_CONTROL, orig_umwait_control_cached);
+
ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "umwait:online",
- umwait_cpu_online, NULL);
+ umwait_cpu_online, umwait_cpu_offline);
+ if (ret < 0) {
+ /*
+ * On failure, the control MSR on all CPUs has the
+ * original control value.
+ */
+ return ret;
+ }
register_syscore_ops(&umwait_syscore_ops);