Re: [Xen-devel] Xen on POWER

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 09/03/18 10:38, awokd wrote:
> On Fri, March 9, 2018 10:03 am, Andrew Cooper wrote:
>> On 09/03/2018 09:37, awokd wrote:
> 
>>
>> Xen currently has x86 and ARM as supported architectures, so there is a
>> reasonable split between common and arch-specific code.  As a start, you'd
>> need to implement enough of the arch stubs to make Power9 build, then work
>> on trying to get it to boot.
>>
>> As a guess, the ARM port is going to be far closer to what you're
>> looking to do than the x86 side.
> 
> Thanks for your reply, that helps. Would it make sense to target 4.8.3
> stable to mostly avoid trying to hit a moving target, then port "up"? I'll
> investigate how ARM support was added too, that's relatively fresh and
> could be used as a model.
> 
>> Porting is one thing, but as you identify below, not  letting it wither
>> is very different.  I can't predict how much ongoing maintenance would be
>> required, but it certainly can't be left alone once "complete".
> 
> Assuming it would be a similar workload to maintaining ARM, any idea if
> we're talking multiple FTEs here or just a fraction of one? Trying to get
> a sense of if it's something that could be maintained in one person's
> off-hours.

If you are serious about it, you need a team. Which is about to stay
around! At least two people, who both know the architecture *and* Xen
well. And it will probably take them more than a year to get something
into a state where you can rely on it in a security sensitive
environment. It gets even worse since you probably need more advanced
features like hardware passthrough for Qubes OS.
You can probably start with knowing only one (Power *or* Xen) well, and
learn your way up, but I wouldn't dare to do an architecture port when
being relatively clueless about details in one of them.

>> There is certainly some interest in getting Power work, and the touted
>> system benefits are clear to see, but porting Xen and maintaining the port
>> is not going to be a trivial task.  If you are up for the challenge, then
>> I think it would a great opportunity.
> 
> Don't expect it to be easy but it sounds like a fun challenge with
> something of value at the end of the tunnel.

Out of curiosity, which Power9 desktop hardware are you looking at for
your Qubes OS desktop OS? And how much better is Power in respect to
vendor lock in (when looking at actually existing, available, capable
CPUs) and to the Spectre/Meltdown issues?
Is porting Xen to Power (aside from the "fun challenge" aspect, which I
would be cautious about) the right answer to you problem?

Cheers,
Andre.

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