On Wed, Jun 12, 2013 at 02:47:11PM +0100, George Dunlap wrote: > On 12/06/13 14:45, Konrad Rzeszutek Wilk wrote: > >On Tue, Jun 11, 2013 at 05:17:45PM +0100, George Dunlap wrote: > >>On 06/11/2013 05:08 PM, konrad wilk wrote: > >>>On 6/11/2013 11:36 AM, George Dunlap wrote: > >>>>On 06/10/2013 10:06 PM, Konrad Rzeszutek Wilk wrote: > >>>>>There are two tool-stack that can instruct the Xen PCI frontend > >>>>>and backend to change states: 'xm' (Python code with a daemon), > >>>>>and 'xl' (C library - does not keep state changes). > >>>>> > >>>>>With the 'xm', the path to disconnect a PCI device (xm pci-detach > >>>>><guest> <BDF>)is: > >>>>> > >>>>>4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)-> > >>>>>4(Connected)->5(Closing*). > >>>>> > >>>>>The * is for states that the tool-stack sets. For 'xl', it is similar: > >>>>> > >>>>>4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)-> 4(Connected) > >>>>> > >>>>>Both of them also tear down the XenBus structure, so the backend > >>>>>state ends up going in the 3(Initialised) and calls > >>>>>pcifront_xenbus_remove. > >>>>So I looked a little bit into this; there are actually two different > >>>>states that happen as part of this handshake. In order to disonnect a > >>>>*device*, xl signals using the *bus* state, like this: > >>>>* Wait for the *bus* to be in state 4(Connected) > >>>>* Set the *device* state to 5(Closing) > >>>>* Set the *bus* state to 7(Reconfiguring) > >>>>* Wait for the *bus* state to return to 4(Connected) > >>>> > >>>>So are all of these states you see the *bus* state? And why would you > >>>>disconnect the whole pci bus if you're only removing one device? > >>>Correct. The stats I enumerated are *bus* states. Not per-device states. > >>>I presume (and I hadn't checked xm) that Xend has some logic to only > >>>disconnect the bus if all of the PCI devices have been disconnected. In > >>>'xl' it does not do that. > >>> > >>>The testing I did was just with one PCI device. > >>Ah, OK -- I see now. The problem is that the code in the Linux side > >>didn't know about the whole "4->7->8->4" thing to unplug a device. > >>In all likelihood, if you had used xm with two devices (so that the > >>bus didn't get disconnected), then you would have run across the > >>same error. > >> > >>So at least part of the problem *is* a bug in Linux. > >Good! Bjorn, would you be OK Ack-ing the patch I sent (attached here > >for reference) or putting it in your queue for Linus? > > > >My plan would be to send it to Linus in the 3.11 merge window. > > One nit -- "to work with the 'xl' toolstack" -- didn't we theorize > this would also be broken with xm if you had two devices passed > through? Yes. I will fix up the title to reflect that shortly (say Friday?) Thanks for your sharp eyes. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
