Re: [Qemu-devel] [PATCH 0/2] Xen pvUSB correction

[Juergen Gross]

On 27/09/16 10:51, Gerd Hoffmann wrote:
> On Mo, 2016-09-26 at 14:43 +0200, Juergen Gross wrote:
>> Trying to use pvUSB in a Xen guest with a qemu emulated USB controller
>> will crash qemu as it tries to attach a pvUSB device to the emulated
>> controller.
> 
> Hmm.  --verbose please.
> 
> While this clearly doesn't do what you intended I think it should not
> have crashed qemu.  pvUSB devices should work on emulated controller
> (and emulated devices should work on the pvUSB controller).  If they
> don't you probably taking shortcuts somewhere which work only for the
> pvUSB device on pvUSB controller case.

Of course a pvUSB device connected by the pvUSB controller is
expecting to be on that controller when doing I/Os. I believe this
was the problem here: The device was attached to an emulated USB
controller and the pvUSB controller started an I/O which confused the
emulated one.

> Please check.

There is something wrong, sure. A pvUSB device ending on the wrong
controller should never receive I/Os from the pvUSB controller. I'll
check that. But this problem is independent from the one solved by
these patches: I have to make sure the device is connected to the
pvUSB controller or otherwise the guest won't be able to access it
the way it was meant to.


Juergen