hvc/xen: fix event channel handling for secondary consoles
authorDavid Woodhouse <dwmw@amazon.co.uk>
Fri, 20 Oct 2023 16:15:27 +0000 (17:15 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 28 Nov 2023 17:19:57 +0000 (17:19 +0000)
commit192e6eba4e72655571907dddcbf2ad61a373cea7
tree1f8dedaecad5b4947d1ccffd8933a935e4b9a768
parent202f4d78d16b5fa920f0d28c22ed2c07f189879a
hvc/xen: fix event channel handling for secondary consoles

commit ef5dd8ec88ac11e8e353164407d55b73c988b369 upstream.

The xencons_connect_backend() function allocates a local interdomain
event channel with xenbus_alloc_evtchn(), then calls
bind_interdomain_evtchn_to_irq_lateeoi() to bind to that port# on the
*remote* domain.

That doesn't work very well:

(qemu) device_add xen-console,id=con1,chardev=pty0
[   44.323872] xenconsole console-1: 2 xenbus_dev_probe on device/console/1
[   44.323995] xenconsole: probe of console-1 failed with error -2

Fix it to use bind_evtchn_to_irq_lateeoi(), which does the right thing
by just binding that *local* event channel to an irq. The backend will
do the interdomain binding.

This didn't affect the primary console because the setup for that is
special — the toolstack allocates the guest event channel and the guest
discovers it with HVMOP_get_param.

Fixes: fe415186b43d ("xen/console: harden hvc_xen against event channel storms")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20231020161529.355083-2-dwmw2@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/tty/hvc/hvc_xen.c