Re: [Xen-devel] [PATCH] xen/pci: Deal with toolstack missing an 'XenbusStateClosing'.

[George Dunlap]

On 06/11/2013 08:29 AM, Jan Beulich wrote:
> > > > On 10.06.13 at 23:06, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 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.
> >
> > When a PCI device is plugged in (xm pci-attach <guest> <BDF>)
> > both of them follow the same pattern:
> > 2(InitWait*), 3(Initialized*), 4(Connected*)->4(Connected).
> >
> > [xen-pcifront ignores the 2,3 state changes and only acts when
> > 4 (Connected) has been reached]
> >
> > The problem is that git commit 3d925320e9e2de162bd138bf97816bda8c3f71be
> > ("xen/pcifront: Use Xen-SWIOTLB when initting if required") introduced
> > a mechanism to initialize the SWIOTLB when the Xen PCI front moves to
> > Connected state. It also had some aggressive seatbelt code check that
> > would warn the user if one tried to change to Connected state without
> > hitting first the Closing state:
> >
> >   pcifront pci-0: PCI frontend already installed!
> >
> > However, that code can be relaxed and we can continue on working
> > even if the frontend is instructed to be the 'Connected' state with
> > no devices and then gets tickled to be in 'Connected' state again.
> >
> > In other words, this 4(Connected)->5(Closing)->4(Connected) state
> > was expected, while 4(Connected)->.... anything but 5(Closing)->4(Connected)
> > was not. This patch removes that aggressive check and allows
> > Xen pcifront to work with the 'xl' toolstack.
>
> I actually think this shouldn't be worked around here, but fixed in
> xl. Any device removed from a guest should be driven towards
> the "Closed" state.

Yeah, that seems pretty obvious to me.  The weird thing is that this 
wasn't noticed before -- does this work in 4.2?  Have you been doing 
this test all along, or has it only broken recently?

I've reproduced it on one of my test boxes; let me see if I can sort it out.

 -George

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