linux-kernel - Re: [PATCH 3.16 47/47] KVM: x86/vPMU: refine kvm

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Date:   Thu, 31 Oct 2019 22:14:15 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        Like Xu <like.xu@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 3.16 47/47] KVM: x86/vPMU: refine kvm_pmu err msg when
 event creation failed

On Fri, 2019-10-25 at 12:05 -0700, Joe Perches wrote:
> On Fri, 2019-10-25 at 19:03 +0100, Ben Hutchings wrote:
> > 3.16.76-rc1 review patch.  If anyone has any objections, please let me know.
> 
> This seems more like an enhancement than a bug fix.
> 
> Is this really the type of patch that is appropriate
> for stable?

Apparently so:

v4.14.135: eba797dbf352 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
v4.19.61: ba27a25df6df KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
v4.4.187: 505c011f9f53 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
v4.9.187: 3984eae04473 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
v5.1.20: edadec197fbf KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
v5.2.3: 9f062aef7356 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed

Ben.

> > ------------------
> > 
> > From: Like Xu <like.xu@...ux.intel.com>
> > 
> > commit 6fc3977ccc5d3c22e851f2dce2d3ce2a0a843842 upstream.
> > 
> > If a perf_event creation fails due to any reason of the host perf
> > subsystem, it has no chance to log the corresponding event for guest
> > which may cause abnormal sampling data in guest result. In debug mode,
> > this message helps to understand the state of vPMC and we may not
> > limit the number of occurrences but not in a spamming style.
> > 
> > Suggested-by: Joe Perches <joe@...ches.com>
> > Signed-off-by: Like Xu <like.xu@...ux.intel.com>
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > [bwh: Backported to 3.16: adjust context]
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > ---
> >  arch/x86/kvm/pmu.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> > @@ -187,8 +187,8 @@ static void reprogram_counter(struct kvm
> >  						 intr ? kvm_perf_overflow_intr :
> >  						 kvm_perf_overflow, pmc);
> >  	if (IS_ERR(event)) {
> > -		printk_once("kvm: pmu event creation failed %ld\n",
> > -				PTR_ERR(event));
> > +		pr_debug_ratelimited("kvm_pmu: event creation failed %ld for pmc->idx = %d\n",
> > +			    PTR_ERR(event), pmc->idx);
> >  		return;
> >  	}
> >  
> > 
-- 
Ben Hutchings
Klipstein's 4th Law of Prototyping and Production:
                               A fail-safe circuit will destroy others.



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