Re: Xen with dom0 pvops on ultra-recent "git tip" kernel on x86_64

[Jeremy Fitzhardinge <jeremy@goop.org>]

Christophe Saout wrote:
> It's not really exciting stuff, mostly some cleanups which were
> moving stuff around and such (and some iotlb dma things which were not
> entirely trivial but pretty straight-forward).
>   

Yeah the iotlb stuff was in a bit of a flux, but I think I understand 
how it ended up.

>> I haven't been brave enough to even attempt starting X; there's a lot of 
>> work to be done if you want to do anything beyond dumb framebuffer.
>>
>> Anyway, in this case, I definitely haven't added this call, so it will 
>> need to be done somewhere.  Does it need to be called once at startup, 
>> or on every context switch?  There may well be a suitable place to hook 
>> this into already, but we can add a new pvop if its really needed.
>>     
>
> Looking at the original Xen kernel the call has to be made on every
> context switch if the io permissions change between the two threads.
> In the past days I have sort of started trying to put some new paravirt
> call together in the various places.  This unfortunately also meant
> changing a bit of the native stuff to pass through a unified
> "set_io_bitmap" call.  I haven't checked if that works, but at least the
> Xen versions of the call doesn't get X up and running.  Now I get a
> black screen and dead machine.  I guess I will have to do some
> debugging. ;-)
>   

There are several pvops calls made already during context switch, so I 
wouldn't be surprised if you can sneak it into one of those (load_sp0 
looks like a candidate, since it's already passed the tss).  Just make 
sure the hypercall gets batched with the rest of the context-switch 
multicall so that the latency doesn't get worse.

> If you're interested, I can send you what I have so far, but I guess you
> have more pressing things to do first. :-)
>   

Yeah, I'm working on rebasing the patch queue at the moment, then I'll 
try to catch up on the various bugs/observations that people have reported.

    J