linux-kernel - Re: [Xen-devel] [PATCH 3/3] x86/xen: sync the CMOS RTC as well as the Xen wallclock

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Date:	Tue, 14 May 2013 17:14:56 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"John Stultz" <john.stultz@...aro.org>
Cc:	"David Vrabel" <david.vrabel@...rix.com>,
	"Jeremy Fitzhardinge" <jeremy.fitzhardinge@...rix.com>,
	"Thomas Gleixner" <tglx@...utronix.de>, <xen-devel@...ts.xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 3/3] x86/xen: sync the CMOS RTC as well
 as the Xen wallclock

>>> On 14.05.13 at 17:59, John Stultz <john.stultz@...aro.org> wrote:
> On 05/14/2013 12:57 AM, Jan Beulich wrote:
>>>>> On 14.05.13 at 02:52, John Stultz <john.stultz@...aro.org> wrote:
>>> Honestly, it seems a little strange to me. If you're running as dom0,
>>> why does HYPERVISOR_dom0_op() not cause the hypervisor to set the cmos
>>> its virtualizing? This seems to mess with the proper virtualization
>>> layering.
>> Thy hypervisor tries to control as little system and peripheral devices
>> as possible, and the CMOS (including the clock) is among those not
>> controlled by it, but by Dom0.
> 
> Huh. So what does calling HYPERVISOR_dom0_op do then?

Here it merely tells the hypervisor that the wall clock changed (so
it can propagate this on to DomU-s).

Jan

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