Re: [PATCHv1] kvm guest: fix uninitialized kvmclock read by KVMguest

From: Igor Mammedov
Date: Thu Jun 20 2013 - 04:40:59 EST


On Wed, 19 Jun 2013 15:29:31 +0200
Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:

> 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.

I'll post this swap shortly, but zeroing out hv_clock at init time,
would be still needed to provide sane values there if ftrace enabled
at that time.

>
> Paolo
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