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

[Joe Perches]

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?

> ------------------
> 
> From: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> 
> 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@xxxxxxxxxxx>
> Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> [bwh: Backported to 3.16: adjust context]
> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> ---
>  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;
>  	}
>  
>