[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] xl PVUSB pass-through

On 07.03.2013 15:11, Pasi KÃrkkÃinen wrote:
> On Thu, Mar 07, 2013 at 10:07:32AM +0000, George Dunlap wrote:
>> On Wed, Mar 6, 2013 at 3:59 PM, Stefan <sstanisi@xxxxxxxxx> wrote:
>>> Good Morning:
>>> Our Xen clusters depend heavily on that feature. The lack of it prevents us
>>> from transitioning to the new toolstack. Currently we use PVUSB to attach a
>>> USB Smartcard reader through our dom0 (SLES 11 SP1) running on an HP Blade
>>> Server with the Token mounted on an internal USB Port to our domU CA server
>>> (SLES 11)
>>> I'd like to know how likely it is to make it to the next release. Does
>>> anyone have a solution that doesn't require PVUSB? I'd like to give a hand
>>> if that can help making PVUSB part of Xen 4.3.
>> For PVUSB to work for any particular VM, you need two things:
>> * PVUSB kernel support in the guest VM and dom0 (or driver domain)
>> * The toolstack has to know how to connect the two.
>> "Classic xen" kernels like those supported by SuSE have PVUSB support,
>> and xend has support for setting up the connection.
>> So regarding PVUSB there are two tasks:
>> 1. Teach xl/libxl how to set up the connection
>> 2. Port PVUSB to pvops kernels.
> PVUSB drivers have already been ported to pvops kernels,
> and the PVUSB drivers can be found from Konrad's git repo.
> What is missing is upstreaming the drivers.

Actually the drivers aren't working well :(
We've tried to use them in Qubes OS, but it is definitely not production ready

Details in this thread (mostly on Qubes-specific tools, but also on kernel
pvusb drivers):

Some quotes (from Alexandre Bezroutchko who was testing/debugging the drivers):
"There might be more than one problem actually. The easiest to reproduce
is kernel memory management issue which reliably causes oopses in
kfree() USB Ethernet adapter is attached. This happens when the backend
tries to free memory block used for USB event handling. I started
debugging it, activated memory-related debugging options in the kernel
and it started crashing much earlier, during bootstrap."

"Another problem I saw is bus resets. When I try to pass-through USB
stick, it gets attached but it takes a minute or so before it starts
working in domU. During this time there are some bus timeout messages or
something in dmesg. This could have something to do with missed events
in frontend-backend communication. I didn't investigate it though, guess
memory management issue needs to be sorted out first."

Trying USBIP (as fallback for PVUSB) points out same problem as in PVUSB:
"The actual problem is USBIP module frees URB transfer buffers
and USB core does the same afterwards. There is a flag controlling this
behaviour (introduced in this patch [1] in kernel). Apparently this flag is
controlled remotely by the frontend, it is mentioned in usbip_protocol.txt
part of the protocol. This is odd, why it can possibly be up to the
frontend to decide whether to free the transfer buffer or not. This
transfer buffer is allocated at stub_rx.c:485, right after URB holding it
is allocated with urb_alloc_urb() at lines 472/475. Eventually the transfer
buffer is freed in stub_main.c:239 and stub_tx.c:31, right before URB is
freed with usb_free_urb(). The latter internally triggers urb_destroy()
which, if URB_FREE_BUFFER flag is set in URB, calls kfree() and actually
causes all the troubles. I think proper solution would be to mask out
URB_FREE_BUFFER from the received transfer flags. There is already some
filtering for the flags stub_rx.c:437 but URB_FREE_BUFFER is explicitly
permitted, which is odd.

By the way, it is possible that pvusb was plagued by the same issue -- at
the first glance I don't find any attempt to filter value of
transfer_flags, normally should happen somewhere around usbback.c:526, but
it does not.

If I'm not mistaken the above problem only affects the backend, so frontend
lockups something else probably. Maybe it is a side effect of my patch to
the lockup problem :). To troubleshoot stalls I figure I can try to run
debugger against the stalled kernel over a virtual serial link and dump
stack trace on the stalled CPU, this might clairfy where the problem is."

Some fix (workaround?) is here:
But this is only one issue of many.

>> It sounds like the main thing you need is to have the xl/libxl
>> support.  This should just be a matter of looking at what xend does in
>> setting up the PVUSB connection, and duplicating that in xl.  If you'd
>> be willing to give that a try, that would be great -- we'd love to
>> help out.
>> If you've never submitted patches before,
>> http://wiki.xen.org/wiki/Submitting_Xen_Patches has some helpful
>> advice.
>> If for some reason PVUSB doesn't make it into 4.3, another option you
>> can explore is running your VMs in PVHVM mode; xl will definitely
>> support USB pass-through for HVM domains in 4.3.
> -- Pasi
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel

Best Regards / Pozdrawiam,
Marek Marczykowski
Invisible Things Lab

Attachment: signature.asc
Description: OpenPGP digital signature

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.