linux-kernel - Re: [PATCHv1] kvm guest: fix uninitialized kvmclock read by KVM guest

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Date:	Wed, 19 Jun 2013 15:29:31 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Batalov Eugene <eabatalov89@...il.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Eugene Batalov <ebatalov@...allels.com>, kvm@...r.kernel.org,
	Igor Mammedov <imammedo@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv1] kvm guest: fix uninitialized kvmclock read by KVM guest

Il 19/06/2013 15:20, Batalov Eugene ha scritto:
> 
> I've missed this detail. It looks like Igor's patch doesn't bring
> secondary cpus kvm_clocksource behavior back to one before the regression,
> Before the regression per_cpu variables are used to allocate
> kvm_pv_clock areas.
> To to usage of percpu variables bootstrap cpu kvm_clock area contents
> were copied to smp secondary cpus kvm_clock areas when they were started.
> Bootstrap cpu kvm_clock area was not zeroed at this time.
> So kvm_pv_clock for secondary cpus never returned "zero" clock before
> the regression.
> 
> During the analysis of the bug I introduced idea to return zero before
> kvm clocksource is initialized for secondary cpus
> just like bootstrap cpu does on kernel boot. You can read that in BZ.

Yes, this is why I prefer to invert the two function calls.  But Igor's
patch fixes the hang (trivially because version is even) and is more
appropriate for -rc6.

Paolo
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