Re: [PATCH] disable clock before rebooting.

[Glauber Costa <gcosta@redhat.com>]

Avi Kivity wrote:
> Glauber Costa wrote:
>> This patch writes 0 (actually, what really matters is that the
>> LSB is cleared) to the system time msr before rebooting/shutting down
>> the machine.
>>
>> Without it, we can have a random memory location being written
>> when the guest comes back
>>      if (!kvm_para_available())
>> @@ -154,6 +181,11 @@ void __init kvmclock_init(void)
>>          pv_time_ops.set_wallclock = kvm_set_wallclock;
>>          pv_time_ops.sched_clock = kvm_clock_read;
>>          pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;
>> +        machine_ops.emergency_restart = kvm_emergency_restart;
>> +        machine_ops.shutdown  = kvm_shutdown;
>> +        machine_ops.restart  = kvm_restart;
>> +        machine_ops.halt  = kvm_halt;
>> +        machine_ops.power_off  = kvm_power_off;
>>          clocksource_register(&kvm_clock);
>>      }
>>  }
>>   
> 
> Oh, I think that these are all unnecessary.  You need to stop the clock 
> only if the memory it uses will be reused.  Halt, shutdown and poweroff 
> clearly don't.  Resets need to go through the host anyway, since they 
> can be invoked without the guest knowing about it.

power off, agreed.
halt, it doesn't really do anything anyway in reboot.c, and is here just 
for "future completeness".

> The only case I can think of where we need to stop the clock is kexec.
> 
as for kexec, it uses precisely the shutdown function, doesn't it?

Or is it crash_shutdown?
Humm, /me looks, and I think it's the later, right?

If this is true and resets goes through the host, then we don't even 
need the header exports. Ingo'll be happy.

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