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

[Julien Grall]

On 06/02/2021 12:09, Jürgen Groß wrote:
> 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@xxxxxxxxxxxxxxx
> > > Reported-by: Julien Grall <julien@xxxxxxx>
> > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > > ---
> > >   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.

Right, this seems to be better than walking over all the CPUs every time 
just for cleaning one bit.

Cheers,

--
Julien Grall