linux-kernel - Re: [PATCH 1/7] xen/events: reset affinity of 2-level event initially

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Date:   Sat, 6 Feb 2021 13:09:19 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Julien Grall <julien@....org>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/7] xen/events: reset affinity of 2-level event initially

On 06.02.21 12:20, Julien Grall wrote:
> Hi Juergen,
> 
> On 06/02/2021 10:49, Juergen Gross wrote:
>> When creating a new event channel with 2-level events the affinity
>> needs to be reset initially in order to avoid using an old affinity
>> from earlier usage of the event channel port.
>>
>> The same applies to the affinity when onlining a vcpu: all old
>> affinity settings for this vcpu must be reset. As percpu events get
>> initialized before the percpu event channel hook is called,
>> resetting of the affinities happens after offlining a vcpu (this is
>> working, as initial percpu memory is zeroed out).
>>
>> Cc: stable@...r.kernel.org
>> Reported-by: Julien Grall <julien@....org>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>   drivers/xen/events/events_2l.c | 20 ++++++++++++++++++++
>>   1 file changed, 20 insertions(+)
>>
>> diff --git a/drivers/xen/events/events_2l.c 
>> b/drivers/xen/events/events_2l.c
>> index da87f3a1e351..23217940144a 100644
>> --- a/drivers/xen/events/events_2l.c
>> +++ b/drivers/xen/events/events_2l.c
>> @@ -47,6 +47,16 @@ static unsigned evtchn_2l_max_channels(void)
>>       return EVTCHN_2L_NR_CHANNELS;
>>   }
>> +static int evtchn_2l_setup(evtchn_port_t evtchn)
>> +{
>> +    unsigned int cpu;
>> +
>> +    for_each_online_cpu(cpu)
>> +        clear_bit(evtchn, BM(per_cpu(cpu_evtchn_mask, cpu)));
> 
> The bit corresponding to the event channel can only be set on a single 
> CPU. Could we avoid the loop and instead clear the bit while closing the 
> port?

This would need another callback.


Juergen


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