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

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

On Fri, Oct 20, 2023 at 05:15:27PM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> 
> 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...