From 51703b71b8114eda6285fbcb5bd808240bef8109 Mon Sep 17 00:00:00 2001 From: Fenghua Yu Date: Fri, 9 Aug 2019 18:40:37 -0700 Subject: [PATCH] x86/umwait: Fix error handling in umwait_init() Currently, failure of cpuhp_setup_state() is ignored and the syscore ops and the control interfaces can still be added even after the failure. But, this error handling will cause a few issues: 1. The CPUs may have different values in the IA32_UMWAIT_CONTROL MSR because there is no way to roll back the control MSR on the CPUs which already set the MSR before the failure. 2. If the sysfs interface is added successfully, there will be a mismatch between the global control value and the control MSR: - The interface shows the default global control value. But, the control MSR is not set to the value because the CPU online function, which is supposed to set the MSR to the value, is not installed. - If the sysadmin changes the global control value through the interface, the control MSR on all current online CPUs is set to the new value. But, the control MSR on newly onlined CPUs after the value change will not be set to the new value due to lack of the CPU online function. 3. On resume from suspend/hibernation, the boot CPU restores the control MSR to the global control value through the syscore ops. But, the control MSR on all APs is not set due to lake of the CPU online function. To solve the issues and enforce consistent behavior on the failure of the CPU hotplug setup, make the following changes: 1. Cache the original control MSR value which is configured by hardware or BIOS before kernel boot. This value is likely to be 0. But it could be a different number as well. Cache the control MSR only once before the MSR is changed. 2. Add the CPU offline function so that the MSR is restored to the original control value on all CPUs on the failure. 3. On the failure, exit from cpumait_init() so that the syscore ops and the control interfaces are not added. Reported-by: Valdis Kletnieks Suggested-by: Thomas Gleixner Signed-off-by: Fenghua Yu Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/1565401237-60936-1-git-send-email-fenghua.yu@intel.com --- arch/x86/kernel/cpu/umwait.c | 39 +++++++++++++++++++++++++++++++++++- 1 file changed, 38 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/umwait.c b/arch/x86/kernel/cpu/umwait.c index 6a204e7336c12..32b4dc9030aa9 100644 --- a/arch/x86/kernel/cpu/umwait.c +++ b/arch/x86/kernel/cpu/umwait.c @@ -17,6 +17,12 @@ */ 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. @@ -52,6 +58,23 @@ static int umwait_cpu_online(unsigned int cpu) return 0; } +/* + * 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 @@ -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); -- 2.39.5