[v2,1/3] hvc/xen: fix event channel handling for secondary consoles

Commit Message

David Woodhouse Oct. 20, 2023, 4:15 p.m. UTC

From: David Woodhouse <[e-mail]>

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 <[e-mail]>
Reviewed-by: Juergen Gross <[e-mail]>
Cc: [e-mail]
---
 drivers/tty/hvc/hvc_xen.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Greg Kroah-Hartman Oct. 21, 2023, 4:32 p.m. UTC | #1

On Fri, Oct 20, 2023 at 05:15:27PM +0100, David Woodhouse wrote:
> From: David Woodhouse <[e-mail]>
> 
> 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")

Nit, our tools complain that the sha1 isn't big enough, "fe415186b43d"
I'll go fix it up...

Patch

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;