linux-kernel - Re: RFC: silencing kvm unimplemented msr spew.

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Date:	Mon, 18 Jul 2016 11:26:50 -0400 (EDT)
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Dave Jones <dsj@...com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Radim Krčmář <rkrcmar@...hat.com>,
	kvm@...r.kernel.org
Subject: Re: RFC: silencing kvm unimplemented msr spew.


> kvm is pretty noisy when you have guests poking at MSRs that the kernel
> doesn't implement.  The conveniently named 'ignore_msrs' option initially
> seemed
> like it was what I was looking for, but it changes the printk instead
> of eliding it.
> 
> Untested patch below converts ignore_msrs to a bitmask and adds an option to
> be
> completely silent. The idea being if after testing, things still work and you
> don't care about those messages, you can deploy in production with the
> silence option.
> 
> Would something like this be acceptable ?

Indeed, ignore_msrs does a completely different thing.  It suppresses
general protection faults in the guest.  It is related to behavior that
KVM injects in the guests, not to the things that KVM spews in the host.

What about just downgrading the printf to KERN_DEBUG?  You could simply
change from vcpu_unimpl to vcpu_debug, but it's probably a good idea to
keep the ratelimiting; there's a kvm_pr_unimpl, so maybe add a new
kvm_pr_debug and vcpu_pr_debug.

Thanks,

Paolo

> 
> 	Dave
> 
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7da5dd2057a9..f9db287118d0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -96,8 +96,12 @@ static void __kvm_set_rflags(struct kvm_vcpu *vcpu,
> unsigned long rflags);
>  struct kvm_x86_ops *kvm_x86_ops __read_mostly;
>  EXPORT_SYMBOL_GPL(kvm_x86_ops);
>  
> -static bool __read_mostly ignore_msrs = 0;
> -module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
> +#define UNHANDLED_UNIMPL_MSR 0
> +#define IGNORE_UNIMPL_MSR    1
> +#define SILENT_UNHANDLED_MSR 2
> +#define SILENT_IGNORED_MSR   3
> +static int __read_mostly ignore_msrs = UNHANDLED_UNIMPL_MSR;
> +module_param(ignore_msrs, int, S_IRUGO | S_IWUSR);
>  
>  unsigned int min_timer_period_us = 500;
>  module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
> @@ -2228,15 +2232,22 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct
> msr_data *msr_info)
>  			return xen_hvm_config(vcpu, data);
>  		if (kvm_pmu_is_valid_msr(vcpu, msr))
>  			return kvm_pmu_set_msr(vcpu, msr_info);
> -		if (!ignore_msrs) {
> +
> +		switch (ignore_msrs) {
> +		case UNHANDLED_UNIMPL_MSR:
>  			vcpu_unimpl(vcpu, "unhandled wrmsr: 0x%x data %llx\n",
> -				    msr, data);
> +				msr, data);
> +			/* fallthrough */
> +		case SILENT_UNHANDLED_MSR:
>  			return 1;
> -		} else {
> +		case IGNORE_UNIMPL_MSR:
>  			vcpu_unimpl(vcpu, "ignored wrmsr: 0x%x data %llx\n",
> -				    msr, data);
> +				msr, data);
> +			/* fallthrough */
> +		case SILENT_IGNORED_MSR:
>  			break;
>  		}
> +		break;
>  	}
>  	return 0;
>  }
>