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

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Date:   Tue, 4 Oct 2022 16:22:00 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Jason Andryuk <jandryuk@...il.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     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 29.08.22 17:15, Jason Andryuk 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
> 
> Have pcifront_detach_devices special-case state Initialised and call
> pcifront_connect_and_init_dma.  Don't use pcifront_try_connect because
> that sets the xenbus state which may throw off the backend.  After
> connecting, skip the remainder of detach_devices since none have been
> initialized yet.  When the backend switches to Reconfigured,
> pcifront_attach_devices will pick them up again.
> 
> Signed-off-by: Jason Andryuk <jandryuk@...il.com>

Reviewed-by: Juergen Gross <jgross@...e.com>

The modifications of the commit message requested by Bjorn can be done
while committing.


Juergen


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