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

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Date:	Tue, 19 Jul 2016 18:12:59 -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.

> On Mon, Jul 18, 2016 at 11:26:50AM -0400, Paolo Bonzini wrote:
> > 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.
>
> Hm, we've certainly got a lot of options in terms of print primitives these
> days.
> 
> We could just do this...
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 1c9c973a7dd9..a80b9a0a5f8c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -423,7 +423,7 @@ struct kvm {
>  #define kvm_debug(fmt, ...) \
>         pr_debug("kvm [%i]: " fmt, task_pid_nr(current), ## __VA_ARGS__)
>  #define kvm_pr_unimpl(fmt, ...) \
> -       pr_err_ratelimited("kvm [%i]: " fmt, \
> +       pr_debug_ratelimited("kvm [%i]: " fmt, \
>                            task_tgid_nr(current), ## __VA_ARGS__)
>  
>  /* The guest did something we don't support. */
> 
> Which I think would have the desired effect, and also gets us dynamic debug
> support for free.

There are some "unimplemented" messages that would be affected and really
should be errors (or even WARNs), but I guess this patch is okay.  Can you
submit it with SoB and all that?

Thanks,

Paolo