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

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Message-ID: <2023102129-humongous-grant-4576@gregkh>
Date:   Sat, 21 Oct 2023 18:32:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.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: Re: [PATCH v2 1/3] hvc/xen: fix event channel handling for secondary
 consoles

On Fri, Oct 20, 2023 at 05:15:27PM +0100, David Woodhouse wrote:
> 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")

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