linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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Date:	Wed, 24 Mar 2010 16:46:05 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>, ziteng.huang@...el.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Fr?d?ric Weisbecker <fweisbec@...il.com>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
	project

On Wed, Mar 24, 2010 at 05:12:55PM +0200, Avi Kivity wrote:
> On 03/24/2010 05:01 PM, Joerg Roedel wrote:
>> $ cd /sys/kvm/guest0
>> $ ls -l
>> -r-------- 1 root root 0 2009-08-17 12:05 name
>> dr-x------ 1 root root 0 2009-08-17 12:05 fs
>> $ cat name
>> guest0
>> $ # ...
>>
>> The fs/ directory is used as the mount point for the guest root fs.
>
> The problem is /sys/kvm, not /sys/kvm/fs.

I am not tied to /sys/kvm. We could also use /proc/<pid>/kvm/ for
example. This would keep anything in the process space (except for the
global list of VMs which we should have anyway).

>> What I meant was: perf-kernel puts the guest-name into every sample and
>> perf-userspace accesses /sys/kvm/guest_name/fs/ later to resolve the
>> symbols. I leave the question of how the guest-fs is exposed to the host
>> out of this discussion. We should discuss this seperatly.
>
> How I see it: perf-kernel puts the guest pid into every sample, and  
> perf-userspace uses that to resolve to a mountpoint served by fuse, or  
> to a unix domain socket that serves the files.

We need a bit more information than just the qemu-pid, but yes, this
would also work out.

>> If a vm breaks into qemu it can access the host file system which is the
>> bigger problem. In this case there is no isolation anymore. From that
>> context it can even kill other VMs of the same user independent of a
>> hypothetical /sys/kvm/.
>
> It cannot.  sVirt labels the disk image and other files qemu needs with  
> the appropriate label, and everything else is off limits.  Even if you  
> run the guest as root, it won't have access to other files.

See my reply to Daniel's email.

>> Yes, but its different from the implementation point-of-view. For the
>> user it surely all plays together.
>
> We need qemu to cooperate for mmio tracing, and we can cooperate with  
> qemu for symbol resolution.  If it prevents adding another kernel API,  
> that's a win from my POV.

Thats true. Probably qemu can inject this information in the
kvm-trace-events stream.

	Joerg

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