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Subject: Re: [PATCH 1/7] xen/events: reset affinity of 2-level event initially
To:     Julien Grall <julien@xen.org>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
Cc:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        stable@vger.kernel.org
References: <20210206104932.29064-1-jgross@suse.com>
 <20210206104932.29064-2-jgross@suse.com>
 <f89567cf-f954-0d97-087e-5e31bfa6d49d@xen.org>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <d2017caa-0ea8-ae9d-d9f6-45be3da20688@suse.com>
Date:   Sat, 6 Feb 2021 13:09:19 +0100
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From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
To: Julien Grall <julien@xen.org>, xen-devel@lists.xenproject.org,
 linux-kernel@vger.kernel.org
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Stefano Stabellini <sstabellini@kernel.org>, stable@vger.kernel.org
Message-ID: <d2017caa-0ea8-ae9d-d9f6-45be3da20688@suse.com>
Subject: Re: [PATCH 1/7] xen/events: reset affinity of 2-level event initially
References: <20210206104932.29064-1-jgross@suse.com>
 <20210206104932.29064-2-jgross@suse.com>
 <f89567cf-f954-0d97-087e-5e31bfa6d49d@xen.org>
In-Reply-To: <f89567cf-f954-0d97-087e-5e31bfa6d49d@xen.org>

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On 06.02.21 12:20, Julien Grall wrote:
> Hi Juergen,
>=20
> 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@vger.kernel.org
>> Reported-by: Julien Grall <julien@xen.org>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>> =C2=A0 drivers/xen/events/events_2l.c | 20 ++++++++++++++++++++
>> =C2=A0 1 file changed, 20 insertions(+)
>>
>> diff --git a/drivers/xen/events/events_2l.c=20
>> 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)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return EVTCHN_2L_NR_CHANNELS;
>> =C2=A0 }
>> +static int evtchn_2l_setup(evtchn_port_t evtchn)
>> +{
>> +=C2=A0=C2=A0=C2=A0 unsigned int cpu;
>> +
>> +=C2=A0=C2=A0=C2=A0 for_each_online_cpu(cpu)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 clear_bit(evtchn, BM(per_c=
pu(cpu_evtchn_mask, cpu)));
>=20
> 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 th=
e=20
> port?

This would need another callback.


Juergen


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