From 0cca790753bf0cab4b070801a46df8e1297c17f6 Mon Sep 17 00:00:00 2001 From: Zachary Amsden Date: Tue, 29 Sep 2009 11:38:35 -1000 Subject: [PATCH] KVM: Kill the confusing tsc_ref_khz and ref_freq variables They are globals, not clearly protected by any ordering or locking, and vulnerable to various startup races. Instead, for variable TSC machines, register the cpufreq notifier and get the TSC frequency directly from the cpufreq machinery. Not only is it always right, it is also perfectly accurate, as no error prone measurement is required. On such machines, when a new CPU online is brought online, it isn't clear what frequency it will start with, and it may not correspond to the reference, thus in hardware_enable we clear the cpu_tsc_khz variable to zero and make sure it is set before running on a VCPU. Signed-off-by: Zachary Amsden Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/x86.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6a31dfb8849c..6f758567831a 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1326,6 +1326,8 @@ out: void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) { kvm_x86_ops->vcpu_load(vcpu, cpu); + if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0)) + per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu); kvm_request_guest_time_update(vcpu); } @@ -3063,9 +3065,6 @@ static void bounce_off(void *info) /* nothing */ } -static unsigned int ref_freq; -static unsigned long tsc_khz_ref; - static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data) { @@ -3074,14 +3073,11 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va struct kvm_vcpu *vcpu; int i, send_ipi = 0; - if (!ref_freq) - ref_freq = freq->old; - if (val == CPUFREQ_PRECHANGE && freq->old > freq->new) return 0; if (val == CPUFREQ_POSTCHANGE && freq->old < freq->new) return 0; - per_cpu(cpu_tsc_khz, freq->cpu) = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new); + per_cpu(cpu_tsc_khz, freq->cpu) = freq->new; spin_lock(&kvm_lock); list_for_each_entry(kvm, &vm_list, vm_list) { @@ -3122,12 +3118,14 @@ static void kvm_timer_init(void) { int cpu; - for_each_possible_cpu(cpu) - per_cpu(cpu_tsc_khz, cpu) = tsc_khz; if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { - tsc_khz_ref = tsc_khz; cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block, CPUFREQ_TRANSITION_NOTIFIER); + for_each_online_cpu(cpu) + per_cpu(cpu_tsc_khz, cpu) = cpufreq_get(cpu); + } else { + for_each_possible_cpu(cpu) + per_cpu(cpu_tsc_khz, cpu) = tsc_khz; } } @@ -4700,6 +4698,14 @@ int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu) int kvm_arch_hardware_enable(void *garbage) { + /* + * Since this may be called from a hotplug notifcation, + * we can't get the CPU frequency directly. + */ + if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { + int cpu = raw_smp_processor_id(); + per_cpu(cpu_tsc_khz, cpu) = 0; + } return kvm_x86_ops->hardware_enable(garbage); } -- 2.20.1