Re: [Minios-devel] Single codebase for para-virtualized guests on x86 and ARM?

[Ajay Garg <ajaygargnsit@xxxxxxxxx>]

Hi Julien.

Thanks for the reply.

On Thu, Apr 5, 2018 at 1:21 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> (+ Stefano and Andre)
>
> On 04/05/2018 04:35 AM, Ajay Garg wrote:
>>
>> Hi Julien.
>>
>> Sorry for restarting this thread, but I was just wondering whether PV
>> on ARM might not provide the following benefits :
>>
>>     * Low overheads as compared to HVM.
>
>
> I don't buy this argument. The overhead is now quite high because with a PV
> solution as you would need to mitigate meltdown.
>
> Furthermore, this require a lot of changes in your guests and I don't see
> any OS community accepting such burden when virtualization extension is
> getting quite widespread on Arm.
>
>>     * Also support systems/procedures with no hardware-virtualization
>> support.
>
>
> There was an attempt to get PV support for Arm before the virtualization
> support was added ([1]). But this is dead.
>
> Do you have any platform in mind you would want to run Xen with no
> virtualization extension?

Ideally, we are targetting low-end arm systems, where
hardware-virtualization is the one thing that we might have to
compromise on.
Beaglebones are an example.


>
>>
>>
>> Of course, the benefits of PV need to be really high, to justify the
>> efforts needed to make the required code-changes for PV-support :P
>
>
> HW virtualization support provides good security and performance with
> limited changes in the guest. Even, x86 community has been discussing to
> deprecate PV and move towards PVH (very similar to Arm guest).
>
> Cheers,
>
> [1] https://wiki.xenproject.org/wiki/Archived/Xen_ARM_(PV)
>
> --
> Julien Grall



-- 
Regards,
Ajay

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