Re: [PATCH 2/2] kvm: pr_guest: don't let guest invoke printk() on host

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Rusty Russell wrote:
> If the guest can invoke a printk(), it can potentially flood the logs,
> causing a host DoS.  We should also indicate *which* guest we're
> talking about.
>
> This patch adds pr_guest (analogous to pr_debug) which ratelimits.
> Not all printk's were replaced: some are only printed once and others
> should probably be replaced by BUG().  I removed the kvm_printf in
> init_rmode_tss: it says nothing that the return value doesn't say.
>
> Coders should be aware that printing in the logs is not particularly
> useful except to give feedback to developers. ie. "should not be used
> for chit-chat".
>
>  int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module);
>  void kvm_exit_arch(void);
> diff -r 3f158ee9df43 drivers/kvm/kvm_main.c
> --- a/drivers/kvm/kvm_main.c	Tue Jul 24 16:22:39 2007 +1000
> +++ b/drivers/kvm/kvm_main.c	Tue Jul 24 16:28:33 2007 +1000
> @@ -425,8 +425,8 @@ inject_gp(struct kvm_vcpu *vcpu, const c
>  	va_list args;
>  
>  	va_start(args, why_fmt);
> -	printk(KERN_DEBUG "kvm: #GP ");
> -	vprintk(why_fmt, args);
> +	if (pr_guest(vcpu, "#GP "))
> +		vprintk(why_fmt, args);
>  	va_end(args);
>  	kvm_arch_ops->inject_gp(vcpu, 0);
>  }
>   

Why go through this optimization?  If it happens frequently, we can just 
remove the printk().  The printk()s are mostly on not-expected-to-happen 
exceptions, and should just be removed if guests do exercise them.


-- 
error compiling committee.c: too many arguments to function


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