[PATCH RFC: kvm tsc virtualization 04/20] Synchronize TSC when a new CPU comes up

[Zachary Amsden]

The loop is written to only work when one master and one slave
enter simultaneously, so properly protect it, and call it when
adding new CPUs.

Signed-off-by: Zachary Amsden <zams...@redhat.com>
---
 arch/x86/kvm/x86.c |   43 ++++++++++++++++++++++++++++++++-----------
 1 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 95e43b9..a599c78 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -729,6 +729,7 @@ static void kvm_set_time_scale(uint32_t tsc_khz, struct 
pvclock_vcpu_time_info *
                 hv_clock->tsc_to_system_mul);
 }
 
+DEFINE_SPINLOCK(kvm_tsc_lock);
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_multiplier);
 static DEFINE_PER_CPU(int, cpu_tsc_shift);
@@ -921,6 +922,21 @@ static void kvm_sync_tsc(void *cpup)
        local_irq_restore(flags);
 }
 
+static void kvm_do_sync_tsc(int cpu)
+{
+       spin_lock(&kvm_tsc_lock);
+       if (raw_smp_processor_id() != tsc_base_cpu) {
+               smp_call_function_single(tsc_base_cpu, kvm_sync_tsc,
+                                        (void *)&cpu, 0);
+               smp_call_function_single(cpu, kvm_sync_tsc, (void *)&cpu, 1);
+       } else {
+               smp_call_function_single(cpu, kvm_sync_tsc, (void *)&cpu, 0);
+               smp_call_function_single(tsc_base_cpu, kvm_sync_tsc,
+                                        (void *)&cpu, 1);
+       }
+       spin_unlock(&kvm_tsc_lock);
+}
+
 static void kvm_write_guest_time(struct kvm_vcpu *v)
 {
        struct timespec ts;
@@ -1634,12 +1650,7 @@ 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)) {
-               unsigned long khz = cpufreq_quick_get(cpu);
-               if (!khz)
-                       khz = tsc_khz;
-               per_cpu(cpu_tsc_khz, cpu) = khz;
-       }
+       BUG_ON(per_cpu(cpu_tsc_khz, cpu) == 0);
        kvm_request_guest_time_update(vcpu);
 }
 
@@ -3505,6 +3516,18 @@ static int kvm_x86_cpu_hotplug(struct notifier_block 
*notifier,
 
        val &= ~CPU_TASKS_FROZEN;
        switch (val) {
+       case CPU_DOWN_PREPARE:
+               if (cpu == tsc_base_cpu) {
+                       int new_cpu;
+                       spin_lock(&kvm_tsc_lock);
+                       for_each_online_cpu(new_cpu)
+                               if (new_cpu != tsc_base_cpu)
+                                       break;
+                       tsc_base_cpu = new_cpu;
+                       spin_unlock(&kvm_tsc_lock);
+               }
+               break;
+
        case CPU_DYING:
        case CPU_UP_CANCELED:
                if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
@@ -3514,6 +3537,7 @@ static int kvm_x86_cpu_hotplug(struct notifier_block 
*notifier,
        case CPU_ONLINE:
                if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
                        per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu);
+               kvm_do_sync_tsc(cpu);
                break;
        }
        return NOTIFY_OK;
@@ -3548,11 +3572,8 @@ static void kvm_timer_init(void)
        per_cpu(cpu_tsc_shift, tsc_base_cpu) = 0;
        per_cpu(cpu_tsc_offset, tsc_base_cpu) = 0;
        for_each_online_cpu(cpu)
-               if (cpu != tsc_base_cpu) {
-                       smp_call_function_single(cpu, kvm_sync_tsc,
-                                                (void *)&cpu, 0);
-                       kvm_sync_tsc((void *)&cpu);
-               }
+               if (cpu != tsc_base_cpu)
+                       kvm_do_sync_tsc(cpu);
        put_cpu();
 }
 
-- 
1.6.5.2

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