linux-kernel - Re: [PATCH] xen-pcifront: Handle missed Connected state

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Message-ID: <CAKf6xpvZNHQyQq9zqNpD0kXFK+pryAKKbRDxoiMkB=PrhvSGKQ@mail.gmail.com>
Date:   Thu, 1 Sep 2022 08:55:41 -0400
From:   Jason Andryuk <jandryuk@...il.com>
To:     Rich Persaud <persaur@...il.com>
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        linux-pci@...r.kernel.org, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen-pcifront: Handle missed Connected state

On Wed, Aug 31, 2022 at 10:35 PM Rich Persaud <persaur@...il.com> wrote:
>
> On Aug 29, 2022, at 11:16 AM, Jason Andryuk <jandryuk@...il.com> wrote:
> >
> > An HVM guest with linux stubdom and 2 PCI devices failed to start as
> > libxl timed out waiting for the PCI devices to be added.  It happens
> > intermittently but with some regularity.  libxl wrote the two xenstore
> > entries for the devices, but then timed out waiting for backend state 4
> > (Connected) - the state stayed at 7 (Reconfiguring).  (PCI passthrough
> > to an HVM with stubdomain is PV passthrough to the stubdomain and then
> > HVM passthrough with the QEMU inside the stubdomain.)
> >
> > The stubdom kernel never printed "pcifront pci-0: Installing PCI
> > frontend", so it seems to have missed state 4 which would have
> > called pcifront_try_connect -> pcifront_connect_and_init_dma
>
> Is there a state machine doc/flowchart for LibXL and Xen PCI device passthrough to Linux? This would be a valuable addition to Xen's developer docs, even as a whiteboard photo in this thread.

I am not aware of one.

-Jason