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Date: Mon, 6 Feb 2012 13:46:21 -0600
From: Scott Wood <scottwood@freescale.com>
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Subject: Re: [Qemu-devel] [RFC] Next gen kvm api
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: qemu-devel <qemu-devel@nongnu.org>, linux-kernel <linux-kernel@vger.kernel.org>, Eric Northup <digitaleric@google.com>, KVM list <kvm@vger.kernel.org>, Avi Kivity <avi@redhat.com>

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@redhat.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.

And sometimes it is a finite resource.  I don't know how x86 does it,
but on at least some powerpc hardware we have a finite, relatively small
number of hardware partition IDs.

-Scott