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

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.


Julien Grall



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