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

From: Scott Wood
Date: Mon Feb 06 2012 - 14:46:27 EST

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@xxxxxxxxxx> 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.


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