linux-kernel - Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side

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Message-ID: <20100322103751.GA3483@elte.hu>
Date:	Mon, 22 Mar 2010 11:37:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	oerg Roedel <joro@...tes.org>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Avi Kivity <avi@...hat.com>,
	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>,
	Zachary Amsden <zamsden@...hat.com>, zhiteng.huang@...el.com,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] Enhance perf to collect KVM guest os statistics from
 host side

* oerg Roedel <joro@...tes.org> wrote:

> > It can decide whether it exposes the files. Nor are there any "security 
> > issues" to begin with.
> 
> I am not talking about security. [...]

You were talking about security, in the portion of your mail that you snipped 
out, and which i replied to:

> >      2. The guest can decide for its own if it want to pass this
> >         inforamtion to the host-perf. No security issues at all.

I understood that portion to mean what it says: that your claim that your 
proposal 'has no security issues at all', in contrast to my suggestion.

> [...] Security was sufficiently flamed about already.

All i saw was my suggestion to allow a guest to securely (and scalably and 
conveniently) integrate/mount its filesystems to the host if both sides (both 
the host and the guest) permit it, to make it easier for instrumentation to 
pick up symbol details.

I.e. if a guest runs then its filesystem may be present on the host side as:

   /guests/Fedora-G1/
   /guests/Fedora-G1/proc/
   /guests/Fedora-G1/usr/
   /guests/Fedora-G1/.../

( This feature would be configurable and would be default-off, to maintain the 
  current status quo. )

i.e. it's a bit like sshfs or NFS or loopback block mounts, just in an 
integrated and working fashion (sshfs doesnt work well with /proc for example) 
and more guest transparent (obviously sshfs or NFS exports need per guest 
configuration), and lower overhead than sshfs/NFS - i.e. without the 
(unnecessary) networking overhead.

That suggestion was 'countered' by an unsubstantiated claim by Anthony that 
this kind of usability feature would somehow be a 'security nighmare'.

In reality it is just an incremental, more usable, faster and more 
guest-transparent form of what is already possible today via:

  - loopback mounts on host
  - NFS exports
  - SMB exports
  - sshfs
  - (and other mechanisms)

I wish there was at least flaming about it - as flames tend to have at least 
some specifics in them.

What i saw instead was a claim about a 'security nightmare', which was, when i 
asked for specifics, was followed by deafening silence. And you appear to have 
repeated that claim here, unwilling to back it up with specifics.

Thanks,

	Ingo
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