Re: [PATCH v3 4/6] KVM-GST: KVM Steal time registration

Avi Kivity
2011-02-15T14:41:30Z

On 02/11/2011 08:19 PM, Glauber Costa wrote:
> 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.
>
>
>
> +static int kvm_register_steal_time(void)
> +{
> + int cpu = smp_processor_id();
> + int low, high, ret;
> + struct kvm_steal_time *st =&per_cpu(steal_time, cpu);
> +
> + if (!hypervisor_steal_time)
> + return 0;

You're using hypervisor_steal_time to communicate the existence of the
feature. Yuck.

> +
> + memset(st, 0, sizeof(*st));
> +
> + low = (int)__pa(st) | 1;

Named constant.

> + high = ((u64)__pa(st)>> 32);
> + ret = wrmsr_safe(MSR_KVM_STEAL_TIME, low, high);

No need for wrmsr_safe() since you're checking the cpuid bit. The other
APIs are nicer (no need to break into two words).

> + printk(KERN_INFO "kvm-stealtime: cpu %d, msr %x:%x\n",
> + cpu, high, low);
> + return ret;
> +}
> +
> #ifdef CONFIG_SMP
> 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);
> + wrmsr(MSR_KVM_STEAL_TIME, 0, 0);

This will trap if running on a hypervisor without this MSR.

> apf_task_wake_all();
> }
>
> @@ -534,6 +557,23 @@ static void __init kvm_apf_trap_init(void)
> set_intr_gate(14,&async_page_fault);
> }
>
> +static u64 kvm_account_steal_time(int cpu)
> +{
> + u64 steal;
> + struct kvm_steal_time *src;
> + int version;
> +
> + src =&per_cpu(steal_time, cpu);
> + do {
> + version = src->version;
> + rmb();
> + steal = src->steal;
> + rmb();
> + } while ((src->version& 1) || (version != src->version));

Check version & 1 instead of src->version & 1, slightly cheaper.

> +
> + return steal;
> +}
> +
>
> index f98d3ea..dcb6a67 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);
> + wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
> native_machine_crash_shutdown(regs);
> }

Make conditional. Needed for the previous wrmsr as well.

> #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);
> + wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
> native_machine_shutdown();
> }
>

Ditto. Is it me, or is the code duplicated?

--
error compiling committee.c: too many arguments to function