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

From: Juergen Gross
Date: Tue Oct 04 2022 - 10:22:20 EST


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@xxxxxxxxx>

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>

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


Juergen

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