linux-kernel - [PATCH v2 1/3] hvc/xen: fix event channel handling for secondary consoles

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Message-Id: <20231020161529.355083-2-dwmw2@infradead.org>
Date:   Fri, 20 Oct 2023 17:15:27 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Roger Pau Monne <roger.pau@...rix.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Dawei Li <set_pte_at@...look.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org, Paul Durrant <paul@....org>
Subject: [PATCH v2 1/3] hvc/xen: fix event channel handling for secondary consoles

From: David Woodhouse <dwmw@...zon.co.uk>

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: fe415186b4 ("xen/console: harden hvc_xen against event channel storms")
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Reviewed-by: Juergen Gross <jgross@...e.com>
Cc: stable@...r.kernel.org
---
 drivers/tty/hvc/hvc_xen.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index 98764e740c07..f24e285b6441 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -433,7 +433,7 @@ static int xencons_connect_backend(struct xenbus_device *dev,
 	if (ret)
 		return ret;
 	info->evtchn = evtchn;
-	irq = bind_interdomain_evtchn_to_irq_lateeoi(dev, evtchn);
+	irq = bind_evtchn_to_irq_lateeoi(evtchn);
 	if (irq < 0)
 		return irq;
 	info->irq = irq;
-- 
2.40.1