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    Subject[PATCH v2 4/6] KVM-GST: KVM Steal time registration
    Date
    Register steal time within KVM. Everytime we sample the steal time
    information, we update a local variable that tells what was the
    last time read. We then account the difference.

    Signed-off-by: Glauber Costa <glommer@redhat.com>
    CC: Rik van Riel <riel@redhat.com>
    CC: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    CC: Peter Zijlstra <peterz@infradead.org>
    CC: Avi Kivity <avi@redhat.com>
    ---
    arch/x86/include/asm/kvm_para.h | 1 +
    arch/x86/kernel/kvm.c | 61 +++++++++++++++++++++++++++++++++++++++
    arch/x86/kernel/kvmclock.c | 2 +
    3 files changed, 64 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
    index 8ba33ed..8210122 100644
    --- a/arch/x86/include/asm/kvm_para.h
    +++ b/arch/x86/include/asm/kvm_para.h
    @@ -89,6 +89,7 @@ struct kvm_vcpu_pv_apf_data {

    extern void kvmclock_init(void);
    extern int kvm_register_clock(char *txt);
    +extern int kvm_register_steal_time(void);


    /* This instruction is vmcall. On non-VT architectures, it will generate a
    diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
    index 33c07b0..30c0fa7 100644
    --- a/arch/x86/kernel/kvm.c
    +++ b/arch/x86/kernel/kvm.c
    @@ -58,6 +58,8 @@ struct kvm_para_state {

    static DEFINE_PER_CPU(struct kvm_para_state, para_state);
    static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
    +static DEFINE_PER_CPU_SHARED_ALIGNED(struct kvm_steal_time, steal_time);
    +static DEFINE_PER_CPU(u64, steal_info);

    static struct kvm_para_state *kvm_para_state(void)
    {
    @@ -489,18 +491,21 @@ static void __init kvm_smp_prepare_boot_cpu(void)
    #ifdef CONFIG_KVM_CLOCK
    WARN_ON(kvm_register_clock("primary cpu clock"));
    #endif
    + WARN_ON(kvm_register_steal_time());
    kvm_guest_cpu_init();
    native_smp_prepare_boot_cpu();
    }

    static void __cpuinit kvm_guest_cpu_online(void *dummy)
    {
    + WARN_ON(kvm_register_steal_time());
    kvm_guest_cpu_init();
    }

    static void kvm_guest_cpu_offline(void *dummy)
    {
    kvm_pv_disable_apf(NULL);
    + native_write_msr(MSR_KVM_STEAL_TIME, 0, 0);
    apf_task_wake_all();
    }

    @@ -534,6 +539,59 @@ static void __init kvm_apf_trap_init(void)
    set_intr_gate(14, &async_page_fault);
    }

    +static u64 kvm_account_steal_time(void)
    +{
    + u64 delta = 0;
    + u64 *last_steal_info, this_steal_info;
    + struct kvm_steal_time *src;
    + int version;
    +
    + src = &get_cpu_var(steal_time);
    + do {
    + version = src->version;
    + rmb();
    + this_steal_info = src->steal;
    + rmb();
    + } while ((src->version & 1) || (version != src->version));
    + put_cpu_var(steal_time);
    +
    + last_steal_info = &get_cpu_var(steal_info);
    +
    + if (likely(*last_steal_info))
    + delta = this_steal_info - *last_steal_info;
    + *last_steal_info = this_steal_info;
    +
    + put_cpu_var(steal_info);
    +
    + /*
    + * using nanoseconds introduces noise, which accumulates easily
    + * leading to big steal time values. We want, however, to keep the
    + * interface nanosecond-based for future-proofness. The hypervisor may
    + * adopt a similar strategy, but we can't rely on that.
    + */
    + delta /= NSEC_PER_MSEC;
    + delta *= NSEC_PER_MSEC;
    +
    + return delta;
    +}
    +
    +
    +int kvm_register_steal_time(void)
    +{
    + int cpu = smp_processor_id();
    + int low, high, ret;
    +
    + if (!hypervisor_steal_time)
    + return 0;
    +
    + low = (int)__pa(&per_cpu(steal_time, cpu)) | 1;
    + high = ((u64)__pa(&per_cpu(steal_time, cpu)) >> 32);
    + ret = native_write_msr_safe(MSR_KVM_STEAL_TIME, low, high);
    + printk(KERN_INFO "kvm-stealtime: cpu %d, msr %x:%x\n",
    + cpu, high, low);
    + return ret;
    +}
    +
    void __init kvm_guest_init(void)
    {
    int i;
    @@ -548,6 +606,9 @@ void __init kvm_guest_init(void)
    if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
    x86_init.irqs.trap_init = kvm_apf_trap_init;

    + if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME))
    + hypervisor_steal_time = kvm_account_steal_time;
    +
    #ifdef CONFIG_SMP
    smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
    register_cpu_notifier(&kvm_cpu_notifier);
    diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
    index f98d3ea..08661c6 100644
    --- a/arch/x86/kernel/kvmclock.c
    +++ b/arch/x86/kernel/kvmclock.c
    @@ -164,6 +164,7 @@ static void __cpuinit kvm_setup_secondary_clock(void)
    static void kvm_crash_shutdown(struct pt_regs *regs)
    {
    native_write_msr(msr_kvm_system_time, 0, 0);
    + native_write_msr(MSR_KVM_STEAL_TIME, 0, 0);
    native_machine_crash_shutdown(regs);
    }
    #endif
    @@ -171,6 +172,7 @@ static void kvm_crash_shutdown(struct pt_regs *regs)
    static void kvm_shutdown(void)
    {
    native_write_msr(msr_kvm_system_time, 0, 0);
    + native_write_msr(MSR_KVM_STEAL_TIME, 0, 0);
    native_machine_shutdown();
    }

    --
    1.7.2.3


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