linux-kernel - Re: [Qemu-devel] [RFC] Next gen kvm api

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Date:	Tue, 07 Feb 2012 17:58:54 +1100
From:	Michael Ellerman <michael@...erman.id.au>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Eric Northup <digitaleric@...gle.com>,
	Avi Kivity <avi@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>
Subject: Re: [Qemu-devel] [RFC] Next gen kvm api

On Mon, 2012-02-06 at 13:46 -0600, Scott Wood wrote:
> On 02/03/2012 04:52 PM, Anthony Liguori wrote:
> > On 02/03/2012 12:07 PM, Eric Northup wrote:
> >> On Thu, Feb 2, 2012 at 8:09 AM, Avi Kivity<avi@...hat.com>  wrote:
> >> [...]
> >>>
> >>> Moving to syscalls avoids these problems, but introduces new ones:
> >>>
> >>> - adding new syscalls is generally frowned upon, and kvm will need
> >>> several
> >>> - syscalls into modules are harder and rarer than into core kernel code
> >>> - will need to add a vcpu pointer to task_struct, and a kvm pointer to
> >>> mm_struct
> >> - Lost a good place to put access control (permissions on /dev/kvm)
> >> for which user-mode processes can use KVM.
> >>
> >> How would the ability to use sys_kvm_* be regulated?
> > 
> > Why should it be regulated?
> > 
> > It's not a finite or privileged resource.
> 
> You're exposing a large, complex kernel subsystem that does very
> low-level things with the hardware.  It's a potential source of exploits
> (from bugs in KVM or in hardware).  I can see people wanting to be
> selective with access because of that.

Exactly.

In a perfect world I'd agree with Anthony, but in reality I think
sysadmins are quite happy that they can prevent some users from using
KVM.

You could presumably achieve something similar with capabilities or
whatever, but a node in /dev is much simpler.

cheers

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