linux-kernel - Re: [KVM timekeeping 10/35] Fix deep C-state TSC desynchronization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4C93EC2C.1000402@redhat.com>
Date:	Fri, 17 Sep 2010 12:31:08 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Jan Kiszka <jan.kiszka@....de>
CC:	Glauber Costa <glommer@...hat.com>, kvm@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [KVM timekeeping 10/35] Fix deep C-state TSC desynchronization

On 09/17/2010 12:09 PM, Zachary Amsden wrote:
> On 09/15/2010 08:27 AM, Jan Kiszka wrote:
>> Am 15.09.2010 14:32, Glauber Costa wrote:
>>> On Wed, Sep 15, 2010 at 10:09:33AM +0200, Jan Kiszka wrote:
>>>>> In any case, I'll proceed with the forcing of unstable TSC and HPET
>>>>> clocksource and see what happens.
>>>> I tried that before, but it did not trigger the issue that kvm-clock
>>>> guests no longer boot properly. This only happens if the TSC is marked
>>>> unstable.
>>> even artificially marked unstable ?
>>>
>> Yes. As soon as I hack tsc_unstable to 1, things go wrong. When I hack
>> it back to 0, guest that wants kvm-clock boots again and seem to run 
>> fine.
>>
>> This is issue #2, I guess. Issue #2 remains that the TSC is marked
>> unstable. I have the feeling that this is bogus, maybe due to lacking
>> suspend/resume awareness? The tsc clocksource does
>>
>>     clocksource_tsc.cycle_last = 0;
>>
>> on resume...
>>
>> Jan
>>
>
> I have now reproduced this exactly.  Shouldn't be long before I have a 
> solution.


Actually, here is what I am seeing: the guest proceeds - in SUPER SLOW 
MO... the effect of this patch negates time when the guest is not 
running.  If the guest is not running because it is idle, negating time 
is the wrong thing to do.  Left to sit, the boot process still proceeds, 
but it goes so slow, you can grow a beard in that time.

Instead, we need wallclock awareness to be preserved.  Should be easy to 
work in one of my later patches which does this.

Zach
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/