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

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Message-Id: <31F127F6-A096-4991-9D4C-1B2E032689A1@gmail.com>
Date:   Wed, 31 Aug 2022 22:35:06 -0400
From:   Rich Persaud <persaur@...il.com>
To:     Jason Andryuk <jandryuk@...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@...ts.xenproject.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen-pcifront: Handle missed Connected state

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.

Rich