linux-kernel - Re: [PATCHv2 2/9] KVM: Expose a version 2 architectural PMU to a guests

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]

Date:	Mon, 07 Nov 2011 15:59:08 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Avi Kivity <avi@...hat.com>
Cc:	Gleb Natapov <gleb@...hat.com>, kvm@...r.kernel.org,
	mtosatti@...hat.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	acme@...stprotocols.net
Subject: Re: [PATCHv2 2/9] KVM: Expose a version 2 architectural PMU to a
 guests

On Mon, 2011-11-07 at 16:46 +0200, Avi Kivity wrote:
> On 11/07/2011 04:34 PM, Peter Zijlstra wrote:
> > On Thu, 2011-11-03 at 14:33 +0200, Gleb Natapov wrote:
> > > +static void kvm_perf_overflow_intr(struct perf_event *perf_event,
> > > +               struct perf_sample_data *data, struct pt_regs *regs)
> > > +{
> > > +       struct kvm_pmc *pmc = perf_event->overflow_handler_context;
> > > +       struct kvm_pmu *pmu = &pmc->vcpu->arch.pmu;
> > > +       if (!test_and_set_bit(pmc->idx, (unsigned long *)&pmu->reprogram_pmi)) {
> > > +               kvm_perf_overflow(perf_event, data, regs);
> > > +               kvm_make_request(KVM_REQ_PMU, pmc->vcpu);
> > > +               /*
> > > +                * Inject PMI. If vcpu was in a guest mode during NMI PMI
> > > +                * can be ejected on a guest mode re-entry. Otherwise we can't
> > > +                * be sure that vcpu is not halted, so we should kick it, but
> > > +                * this is impossible from NMI context. Do it from irq work
> > > +                * instead.
> > > +                */
> > > +               if (!kvm_is_in_guest())
> > > +                       irq_work_queue(&pmc->vcpu->arch.pmu.irq_work);
> > > +               else
> > > +                       kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
> > > +       }
> > > +} 
> >
> > I'm not sure I get this, since the counters are vcpu task bound and only
> > count while the guest is running as per (144d31e6f19) how can we get an
> > NMI outside of guest context with the vcpu not halted?
> 
> PMI skew.  Do we know how bad it can get?

You're talking about the PMI getting asserted before leaving guest mode
but not getting ran until after we left guest mode?

But in that case we know the guest is stopped, right? So we can simply
set that REQ_PMI bit and have guest entry sort things, no?
--
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/