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Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project
From: Peter Zijlstra <peterz@infradead.org>
To: Joerg Roedel <joro@8bytes.org>
Cc: Avi Kivity <avi@redhat.com>, Anthony Liguori <anthony@codemonkey.ws>,
       Ingo Molnar <mingo@elte.hu>, Pekka Enberg <penberg@cs.helsinki.fi>,
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       ziteng.huang@intel.com, Arnaldo Carvalho de Melo <acme@redhat.com>,
       Fr?d?ric Weisbecker <fweisbec@gmail.com>,
       Gregory Haskins <ghaskins@novell.com>
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Date: Wed, 24 Mar 2010 17:45:59 +0100
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On Wed, 2010-03-24 at 17:23 +0100, Joerg Roedel wrote:
> On Wed, Mar 24, 2010 at 05:03:42PM +0100, Peter Zijlstra wrote:
> > On Wed, 2010-03-24 at 16:01 +0100, Joerg Roedel wrote:
> > 
> > > 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.
> > 
> > I'd much prefer a pid like suggested later, keeps the samples smaller.
> > 
> > But that said, we need guest kernel events like mmap and context
> > switches too, otherwise we simply can't make sense of guest userspace
> > addresses, we need to know the guest address space layout.
> 
> With the filesystem approach all we need is the pid of the guest
> process. Then we can access proc/<pid>/maps of the guest and read out the
> address space layout, no?

No, what if it maps new things after you read it? But still getting the
pid of the guest process seems non trivial without guest kernel support.