Re: [Qemu-devel] [PATCH v5 10/12] hw/mips: malta: Add KVM support

James Hogan
2014-06-20T11:28:57Z

On 20/06/14 12:19, Aurelien Jarno wrote:
> On Fri, Jun 20, 2014 at 12:38:30PM +0200, Paolo Bonzini wrote:
>> Il 20/06/2014 11:10, Aurelien Jarno ha scritto:
>>>> My idea was to add a machines-specific option umkernel=on, and require it
>>>> in order to run KVM. Later we can add umkernel=on support for TCG as well,
>>>> while umkernel=off with KVM requires virtualization extensions.
>>>>
>>>> The same option can disable pflash boot.
>>>>
>>>> What do you think?
>>>
>>> For what I understand the current KVM support in MIPS uses trap and
>>> emulate and thus doesn't need hardware support, just a recent kernel
>>> with the option enabled.
>>
>> Yes, but work to support virtualization extensions is underway.
>> Patches were posted a few months ago.
>>
>>> That's why I do wonder if there is a real point
>>> in supporting UM kernels in TCG mode.
>>
>> Debugging, mainly. It is sometimes useful to compare TCG with KVM
>> on x86, and I suppose it could be the same on MIPS.
>
> Ok, then we can indeed add a umkernel option, which is always enabled
> with KVM, and which disable the flash (and why not other devices) in
> that case.
>
> At some point it might be a good idea to add a specific machine for
> emulation/virtualization, like it is done on ARM, which do not have to
> handle this kind of devices, and which does not have all the current
> limitations of the Malta board.

FYI Cavium have been working on a para-virtualised machine which they
use with their VZ KVM implementation. They're using lkvm, but I expect
it will make sense to port that to QEMU too.

lkvm patchset (applied):
https://www.mail-archive.com/kvm%40vger.kernel.org/msg102792.html

linux kernel patchset (merged in v3.16-rc1):
https://www.mail-archive.com/kvm%40vger.kernel.org/msg102806.html

Cheers
James