Re: [PATCH 3.16 47/47] KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed

Ben Hutchings
2019-10-31T22:14:41Z

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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@linux.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@perches.com>
> > Signed-off-by: Like Xu <like.xu@linux.intel.com>
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > [bwh: Backported to 3.16: adjust context]
> > Signed-off-by: Ben Hutchings <ben@decadent.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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