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

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

> -----Original Message-----
> From: George Dunlap
> Sent: 28 April 2016 09:51
> To: Martin Cerveny
> Cc: xen-devel@lists.xensource.com; Paolo Bonzini; Paul Durrant
> Subject: Re: [Xen-devel] Overlaped PIO with multiple ioreq_server
> (Xen4.6.1)
> 
> On Wed, Apr 27, 2016 at 8:38 PM, Martin Cerveny <martin@c-home.cz>
> wrote:
> > Hello.
> >
> > I have problem with multiple ioreq_servers
> > server 1 (emulates VGA) and server 2 (qemu).
> >
> > Emulation VGA server maps VGA PIO registers (3c0-3cf, 3b4-3b5 ...)
> > Qemu maps "all" PIO space (0-ffff)
> > (ref:
> > http://xenbits.xen.org/gitweb/?p=qemu-
> xen.git;a=blob;f=exec.c;h=46fe70ed49f85d0638061aa5b09f1f9d521b0bd3;hb
> =18f2ce4bfe67f9b38143d9d96207e49c92b6881c#l2007
> > )
> > Xen does not check overlap errors between ioreq_servers
> > (ref:
> >
> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/hvm/hvm
> .c;h=186e01e3b05a0264e8f4538b226da2feed50d11a;hb=d77bac5c064ffb9dbb
> 5b89b55b89853f1b784ebf#l1252
> > )
> > Xen choose "first match"
> > (ref:
> >
> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/hvm/hvm
> .c;h=186e01e3b05a0264e8f4538b226da2feed50d11a;hb=d77bac5c064ffb9dbb
> 5b89b55b89853f1b784ebf#l2594
> > )
> >
> > In my case all requests to VGA PIO are sent to qemu (qemu VGA is disabled
> > with parameter "-display none"/"-vga none") and dropped.
> > Emulation VGA server receives only memory updates (eg. a0000-bffff).
> >
> > Is this problem resolved in updates (actual code looks the same (ioreq.c)) ?
> > Is there any prioritization between ioreq_servers (but it is probably bad
> > idea) ?
> > Should the IO mapping check overlap between ioreq_servers (but it is
> > probably bad idea) ?
> > Should the qemu IO map only emulated areas (why it needs all ?) ?
> 
> I think the idea was that devicemodels should only request IO ports
> for devices they actually intend to emulate.  It sounds like this is
> an unfinished implementation inside of qemu.
> 

Does QEMU really map all of PIO space? That's not the behaviour I observed last time I looked. The memory_region_init_io() function just initializes QEMU's internal handlers IIRC; I think the IO ranges get registered with Xen when the individual device models initialize. If you look in xen_common.h (in QEMU) then you'll note that there are tracepoints on all the map/unmap calls, so if you use an events list such as the following:

xen_map_mmio_range
xen_unmap_mmio_range
xen_map_portio_range
xen_unmap_portio_range
xen_map_pcidev
xen_unmap_pcidev
xen_ioreq_server_create
xen_ioreq_server_destroy
xen_ioreq_server_state

then you'll be able to see all the individual range registrations and deregistrations as well the ioreq server lifecycle.

FWIW, I have my own vga/kbd/mouse emulator which I've happily used alongside QEMU (see http://xenbits.xen.org/gitweb/?p=people/pauldu/demu.git;a=shortlog;h=refs/heads/console), although it's been a while since I last tested it.

  Paul

>  -George
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