Re: [Xen-devel] Overlaped PIO with multiple ioreq_server (Xen4.6.1)

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of
> Paul Durrant
> Sent: 09 May 2016 14:00
> To: Paolo Bonzini; Martin Cerveny
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; George Dunlap
> Subject: Re: [Xen-devel] Overlaped PIO with multiple ioreq_server
> (Xen4.6.1)
> 
> > -----Original Message-----
> > From: Paolo Bonzini [mailto:pbonzini@xxxxxxxxxx]
> > Sent: 09 May 2016 13:56
> > To: Paul Durrant; Martin Cerveny
> > Cc: George Dunlap; xen-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] Overlaped PIO with multiple ioreq_server
> > (Xen4.6.1)
> >
> >
> >
> > On 28/04/2016 13:25, Paul Durrant wrote:
> > >> Maybe you are lucky, qemu is registered before your own demu
> > >> emulator.
> > >
> > > I guess I was lucky.
> >
> > Yeah, QEMU has been doing that since 2013 (commit 3bb28b7, "memory:
> > Provide separate handling of unassigned io ports accesses", 2013-09-05).
> >
> > >> I used for testing your "demu" 2 years ago, now extending Citrix
> > >> "vgpu", all was fine up to xen 4.5.2 (with qemu 2.0.2) but
> > >> problem begin when I switched to 4.6.1 (with qemu 2.2.1), but it
> > >> maybe lucky timing in registration.
> > >
> > > I think Xen should really be spotting range overlaps like this, but
> > > the QEMU<->Xen interface will clearly need to be fixed to avoid the
> > > over-claiming of I/O ports like this.
> >
> > If the handling of unassigned I/O ports is sane in Xen (in QEMU they
> > return all ones and discard writes),
> 
> Yes, it does exactly that.
> 
> > it would be okay to make the
> > background 0-65535 range conditional on !xen_enabled().  See
> > memory_map_init() in QEMU's exec.c file.
> >
> 
> Cool. Thanks for the tip. Will have a look at that now.
> 

Looks like creation of the background range is required. (Well, when I simply 
#if 0-ed out creating it QEMU crashed on invocation). So, I guess I need to be 
able to spot, from the memory listener callback in Xen, when a background range 
is being added so it can be ignored. Same actually goes for memory as well as 
I/O, since Xen will handle access to unimplemented MMIO ranges in a similar 
fashion.

  Paul 

> Cheers,
> 
>   Paul
> 
> > Paolo
> 
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