Re: Overlaped PIO with multiple ioreq_server (Xen4.6.1)

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> Sent: 09 May 2016 17:18
> To: Paul Durrant; Martin Cerveny
> Cc: xen-devel@lists.xensource.com; George Dunlap
> Subject: Re: [Xen-devel] Overlaped PIO with multiple ioreq_server
> (Xen4.6.1)
> 
> 
> 
> On 09/05/2016 18:14, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Paul Durrant
> >> Sent: 09 May 2016 17:02
> >> To: Paul Durrant; Paolo Bonzini; Martin Cerveny
> >> Cc: xen-devel@lists.xensource.com; George Dunlap
> >> Subject: RE: [Xen-devel] Overlaped PIO with multiple ioreq_server
> >> (Xen4.6.1)
> >>
> >>> -----Original Message-----
> >>> From: Xen-devel [mailto:xen-devel-bounces@lists.xen.org] On Behalf
> Of
> >>> Paul Durrant
> >>> Sent: 09 May 2016 14:00
> >>> To: Paolo Bonzini; Martin Cerveny
> >>> Cc: xen-devel@lists.xensource.com; George Dunlap
> >>> Subject: Re: [Xen-devel] Overlaped PIO with multiple ioreq_server
> >>> (Xen4.6.1)
> >>>
> >>>> -----Original Message-----
> >>>> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> >>>> Sent: 09 May 2016 13:56
> >>>> To: Paul Durrant; Martin Cerveny
> >>>> Cc: George Dunlap; xen-devel@lists.xensource.com
> >>>> 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.
> >>
> >
> > In fact, this patch seems to do the trick for I/O:
> >
> > diff --git a/xen-hvm.c b/xen-hvm.c
> > index 039680a..8ab44f0 100644
> > --- a/xen-hvm.c
> > +++ b/xen-hvm.c
> > @@ -510,8 +510,12 @@ static void xen_io_add(MemoryListener *listener,
> >                         MemoryRegionSection *section)
> >  {
> >      XenIOState *state = container_of(listener, XenIOState, io_listener);
> > +    MemoryRegion *mr = section->mr;
> >
> > -    memory_region_ref(section->mr);
> > +    if (mr->ops == &unassigned_io_ops)
> > +        return;
> > +
> > +    memory_region_ref(mr);
> >
> >      xen_map_io_section(xen_xc, xen_domid, state->ioservid, section);
> >  }
> > @@ -520,10 +524,14 @@ static void xen_io_del(MemoryListener *listener,
> >                         MemoryRegionSection *section)
> >  {
> >      XenIOState *state = container_of(listener, XenIOState, io_listener);
> > +    MemoryRegion *mr = section->mr;
> > +
> > +    if (mr->ops == &unassigned_io_ops)
> > +        return;
> >
> >      xen_unmap_io_section(xen_xc, xen_domid, state->ioservid, section);
> >
> > -    memory_region_unref(section->mr);
> > +    memory_region_unref(mr);
> >  }
> 
> Looks good, feel free to Cc me if you send it to qemu-devel (though I'll
> let Anthony merge it).

Cool, thanks.

  Paul

> 
> Paolo
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