Re: [External] Re: [RFC: timer passthrough 1/9] KVM: vmx: hook set_next_event for getting the host tscd

Zhimin Feng
2021-02-23T13:09:34Z

Hi tglx

This question is very nice,  we should be considered to judge whether
the current active device is the tsc deadline timer. I will fix this in V2.

Thanks

Zhimin

在 2021/2/6 上午2:11, Thomas Gleixner 写道:
> On Fri, Feb 05 2021 at 18:03, Zhimin Feng wrote:
>> @@ -520,6 +521,24 @@ struct kvm_vcpu_hv {
>> cpumask_t tlb_flush;
>> };
>>
>> +enum tick_device_mode {
>> + TICKDEV_MODE_PERIODIC,
>> + TICKDEV_MODE_ONESHOT,
>> +};
>> +
>> +struct tick_device {
>> + struct clock_event_device *evtdev;
>> + enum tick_device_mode mode;
>> +};
> There is a reason why these things are defined in a header file which is
> not public. Nothing outside of kernel/time/ has to fiddle with
> this. Aside of that how are these things supposed to stay in sync?
>
>> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
>> index 6c9c342dd0e5..bc50f4a1a7c0 100644
>> --- a/kernel/time/tick-common.c
>> +++ b/kernel/time/tick-common.c
>> @@ -26,6 +26,7 @@
>> * Tick devices
>> */
>> DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
>> +EXPORT_SYMBOL_GPL(tick_cpu_device);
> Not going to happen ever.
>
>> +#define TSC_DIVISOR 8
>> +static DEFINE_PER_CPU(struct timer_passth_info, passth_info);
>> +
>> +static int override_lapic_next_event(unsigned long delta,
>> + struct clock_event_device *evt)
>> +{
>> + struct timer_passth_info *local_timer_info;
>> + u64 tsc;
>> + u64 tscd;
>> +
>> + local_timer_info = &per_cpu(passth_info, smp_processor_id());
>> + tsc = rdtsc();
>> + tscd = tsc + (((u64) delta) * TSC_DIVISOR);
>> + local_timer_info->host_tscd = tscd;
>> + wrmsrl(MSR_IA32_TSCDEADLINE, tscd);
>> + return 0;
>> +}
>> +
>> +static void vmx_host_timer_passth_init(void *junk)
>> +{
>> + struct timer_passth_info *local_timer_info;
>> + int cpu = smp_processor_id();
>> +
>> + local_timer_info = &per_cpu(passth_info, cpu);
>> + local_timer_info->curr_dev = per_cpu(tick_cpu_device, cpu).evtdev;
>> + local_timer_info->orig_set_next_event =
>> + local_timer_info->curr_dev->set_next_event;
>> + local_timer_info->curr_dev->set_next_event = override_lapic_next_event;
> So when loading the KVM module you steal the set_next_event pointer of
> the clock event device which is currently active. What guarantees that
>
> 1) The current active device is the tsc deadline timer
> 2) The active device does not change
>
> Nothing.
>
> Thanks,
>
> tglx