linux-kernel - Re: [PATCH v2 3/5] xen/events: only register debug interrupt for 2-level events

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Message-ID: <b21d3544-2257-dee5-222d-f4dade94d167@suse.com>
Date:   Thu, 22 Oct 2020 15:17:52 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Jürgen Groß <jgross@...e.com>
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 3/5] xen/events: only register debug interrupt for
 2-level events

On 22.10.2020 15:09, Jürgen Groß wrote:
> On 22.10.20 12:35, Jan Beulich wrote:
>> On 22.10.2020 11:49, Juergen Gross wrote:
>>> @@ -2080,10 +2080,12 @@ void __init xen_init_IRQ(void)
>>>   	int ret = -EINVAL;
>>>   	evtchn_port_t evtchn;
>>>   
>>> -	if (fifo_events)
>>> +	if (xen_fifo_events)
>>>   		ret = xen_evtchn_fifo_init();
>>> -	if (ret < 0)
>>> +	if (ret < 0) {
>>>   		xen_evtchn_2l_init();
>>> +		xen_fifo_events = false;
>>> +	}
>>
>> Another note: While it may not matter right here, maybe better
>> first set the variable and the call the function?
> 
> I don't think this is really important, TBH.
> 
> This code is executed before other cpus are up and we'd have major
> other problems in case the sequence would really matter here.

Fair enough; I was thinking in particular that it ought to be
legitimate for xen_evtchn_2l_init() to BUG_ON(xen_fifo_events).

Jan