linux-kernel - Re: [PATCH v2 1/2] keep guest wallclock in sync with host clock

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: <20090908200004.GA20785@amt.cnet>
Date:	Tue, 8 Sep 2009 17:00:04 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com
Subject: Re: [PATCH v2 1/2] keep guest wallclock in sync with host clock

On Tue, Sep 08, 2009 at 04:37:52PM -0300, Glauber Costa wrote:
> On Tue, Sep 08, 2009 at 03:41:59PM -0300, Marcelo Tosatti wrote:
> > On Wed, Sep 02, 2009 at 10:34:57AM -0400, Glauber Costa wrote:
> > > KVM clock is great to avoid drifting in guest VMs running ontop of kvm.
> > > However, the current mechanism will not propagate changes in wallclock value
> > > upwards. This effectively means that in a large pool of VMs that need accurate timing,
> > > all of them has to run NTP, instead of just the host doing it.
> > > 
> > > Since the host updates information in the shared memory area upon msr writes,
> > > this patch introduces a worker that writes to that msr, and calls do_settimeofday
> > > at fixed intervals, with second resolution. A interval of 0 determines that we
> > > are not interested in this behaviour. A later patch will make this optional at
> > > runtime
> > > 
> > > Signed-off-by: Glauber Costa <glommer@...hat.com>
> > 
> > As mentioned before, ntp already does this (and its not that heavy is
> > it?).
> > 
> > For example, if ntp running on the host, it avoids stepping the clock
> > backwards by slow adjustment, while the periodic frequency adjustment on
> > the guest bypasses that.
> 
> Simple question: How do I run ntp in guests without network?

You don't.

--
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/