Zachary Amsden wrote:
> 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 <zamsden@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 26 ++++++++++++++++----------
> 1 files changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 15d2ace..de4ce8f 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);
> }
>
> @@ -3061,9 +3063,6 @@ 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)
> {
> @@ -3072,14 +3071,11 @@ 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) {
> @@ -3120,12 +3116,14 @@ 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);
This doesn't build for !CONFIG_CPU_FREQ.
Jan
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