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Date: Mon, 22 Mar 2010 21:47:57 +0200
From: Avi Kivity <avi@redhat.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Anthony Liguori <anthony@codemonkey.ws>,
       Pekka Enberg <penberg@cs.helsinki.fi>,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Sheng Yang <sheng@linux.intel.com>, linux-kernel@vger.kernel.org,
       kvm@vger.kernel.org, Marcelo Tosatti <mtosatti@redhat.com>,
       oerg Roedel <joro@8bytes.org>, Jes Sorensen <Jes.Sorensen@redhat.com>,
       Gleb Natapov <gleb@redhat.com>, Zachary Amsden <zamsden@redhat.com>,
       ziteng.huang@intel.com, Arnaldo Carvalho de Melo <acme@redhat.com>,
       Fr?d?ric Weisbecker <fweisbec@gmail.com>,
       Gregory Haskins <ghaskins@novell.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project
References: <20100322124428.GA12475@elte.hu> <4BA76810.4040609@redhat.com> <20100322143212.GE14201@elte.hu> <4BA7821C.7090900@codemonkey.ws> <20100322155505.GA18796@elte.hu> <4BA796DF.7090005@redhat.com> <20100322165107.GD18796@elte.hu> <4BA7A406.9050203@redhat.com> <20100322173400.GB15795@elte.hu> <4BA7B9E0.5080009@codemonkey.ws> <20100322192739.GE21919@elte.hu>
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On 03/22/2010 09:27 PM, Ingo Molnar wrote:
>
>> If your position basically boils down to, we can't trust userspace
>> and we can always trust the kernel, I want to eliminate any
>> userspace path, then I can't really help you out.
>>      
> Why would you want to 'help me out'? I can tell a good solution from a bad one
> just fine.
>    

You are basically making a kernel implementation a requirement, instead 
of something that follows from the requirement.

> You should instead read the long list of disadvantages above, invert them and
> list then as advantages for the kernel-based vcpu enumeration solution, apply
> common sense and go admit to yourself that indeed in this situation a kernel
> provided enumeration of vcpu contexts is the most robust solution.
>    

Having qemu enumerate guests one way or another is not a good idea IMO 
since it is focused on one guest and doesn't have a system-wide entity.  
A userspace system-wide entity will work just as well as kernel 
implementation, without its disadvantages.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.