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

[Christophe Saout <christophe@xxxxxxxx>]

Hi Jeremy,

> > The native Xen kernel has an arch/x86/kernel/ioport-xen.c which calls:
> >
> >     HYPERVISOR_physdev_op(PHYSDEVOP_set_iobitmap, &set_iobitmap);
> >
> > Is this a feature mabye still missing from the paravirtualized Xen?
> >
> > If yes, what would it take?  A new paravirt call?
>
> Firstly, thanks a lot for trying out the pvops dom0 and doing so much 
> debugging on it.

You're welcome.  It's not like I really need it, but it would simply
things a bit and I just love to play with bleeding edge stuff.

>   I'm still catching up on my rather daunting email 
> backlog - including your torrent of messages - so feel free to remind me 
> about/resent anything important which still needs looking at.

Don't worry.  As you might have noticed, the patches in patches.hg have
sort of fallen behind the tip tree.  I have forward-ported them to the
version from last weekend (no guarantee that I did not put a bug in
there, but at least it compiles).  It's in my git tree I was
referencing, but I didn't bother putting everything back into the patch
it belongs, that would need some fixing up.  In case you are planning on
having some of the patches merged upstream soon, you can take it from
there.  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).

> 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. ;-)

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

Cheers,
        Christophe



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