[Qemu-devel] Re: [PATCH] spice: add qxl device

[Michael S. Tsirkin]

On Wed, Nov 17, 2010 at 06:02:39PM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> >>>>Better don't try ...
> >>>
> >>>Better prevent it then?
> >>
> >>How can I do that?
> 
> Question still stands:  Is there some way to disable hotplug for
> certain pci devices?

Not sure. It's really a work-around bug, maybe it's better to fix
it properly.

> >>  How does this work btw?  Only
> >>one vga adapter can drive the legacy vga ports, right?  Is there
> >>some way to enable/disable this per vga device?
> >
> >Yes, just disable IO memory.
> 
> This is supposed to disable legacy vga ports (0x03c0+) too?

Sure.

> >>  If so: does qemu
> >>emulate this correctly?
> >
> >It mostly does.
> 
> I doubt it actually enables/disables the legacy vga ports.

I'll check when I have the time. We can fix it if it doesn't,

> >But the counter wrapping will at least in theory crash qemu,
> >this is an even bigger problem than a guest crash.
> 
> I can put it a limit at one million hotplugs or so ...

How about a simple allocator? With at most 256 devices
on a pci bus * 8 functions, it need not be hard: just
a long long bitmask with ffsll used to find a free bit.

Also - what is the ID used for? What happens if it's not
unique?

> >>  I also don't see the point in plugging a display like
> >>mad.
> >
> >Just to see if you can exploit some memory corruption maybe?
> 
> Can the guest do that without the hosts help?
> Especially plugging *in* something?
> 
> cheers,
>   Gerd

No, but a monitor user connected to qemu over a qmp socket can do this.

-- 
MST