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:
> On Tue, 2007-07-24 at 14:01 +0300, Avi Kivity wrote:
>   
>> Rusty Russell wrote:
>>     
>>> KVM *will* be used to run malicious guests.  That's going to be hard to
>>> lock down later, so I figure we should start now.
>>>       
>> There's no reason to make this KERN_WARN.  There's nothing wrong with 
>> the host, and there may not be anything wrong with the guest.  These are 
>> only used to see if the guest did something unexpected, which may or may 
>> not be a problem (a kvm test suite would certainly trigger them).
>>
>> Perhaps we should make them conditional on a debug flag, or remove them 
>> completely.  Most of them don't ever trigger, and i don't expect we can 
>> bring up a new guest solely using these printks.
>>     
>
> So should there be two routines?  pr_unimpl() (KERN_ERR) and
> pr_unexpected() (KERN_DEBUG) maybe.  Both ratelimited, with nice
> formatting to tell user which machine & cpu for reporting when there's a
> problem...
>
> Turning them off is your call: have they proven useful?
>   

Unimplemented has certainly proven useful, mostly with msrs (which we 
implement on demand).

The unexpected ones are usually badly implemented (as you discovered 
with the set_cr4() bug), so if something goes wrong and they show up, 
that's a hint.  However, that was useful during initial bringup, and 
these things don't happen anymore, so it's probably better to remove 
them than to introduce a new kernel subsystem after a 400-message thread 
on kvm-devel.  They don't rhyme anyway.

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


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