From: Valentin Schneider <valentin.schneider@arm.com>
To: Woody Lin <woodylin@google.com>
Cc: Ingo Molnar <mingo@redhat.com>, Ben Segall <bsegall@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/scs: Reset the shadow stack when idle_task_exit
Date: Wed, 13 Oct 2021 14:32:51 +0100 [thread overview]
Message-ID: <87tuhljbi4.mognet@arm.com> (raw)
In-Reply-To: <CAHn4DedEV953QULZLAPOuXyHAw_mWRTdFj8bSm6zk3rNjFJj-A@mail.gmail.com>
On 13/10/21 09:22, Woody Lin wrote:
> On Tue, Oct 12, 2021 at 6:57 PM Valentin Schneider <valentin.schneider@arm.com> wrote:
>> On 12/10/21 18:35, Woody Lin wrote:
>> > unpoison looks more like an one-time thing to me; the idle tasks will
>> > reuse the same stack pages until system resets, so I think we don't need
>> > to re-unpoison that during hotplugging as long as it's unpoisoned in
>> > 'init_idle'.
>> >
>>
>> I would tend to agree, but was bitten by s390 freeing some memory on
>> hot-unplug and re-allocating it upon hotplug:
>>
>> 6a942f578054 ("s390: preempt: Fix preempt_count initialization")
>>
>> This makes me doubt whether we can assert the idle task stack pages are
>> perennial vs hotplug on all architectures.
>
> I made a quick study on memory-hotplug and seems that only memory contains
> nothing other than migratable pages can be unplugged. So process stack
> pages should not be a concern for this, since which is an unmovable
> memory.
>
> However I don't have a chance to work on a system that enables
> memory-hotplug so far, so couldn't verify this assumption further. Guess
> we can create a separate thread to clarify this more.
>
That sounds sensible; I'll try to dig some more into this.
As for the SCS change, someone might argue for placing this elsewhere in
the hotplug path, but that looks fine to me:
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> Regards,
> Woody
>
>>
>> >>
>> >> > }
>> >> >
>> >> > --
>> >> > 2.33.0.882.g93a45727a2-goog
next prev parent reply other threads:[~2021-10-13 13:33 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-12 8:35 [PATCH] sched/scs: Reset the shadow stack when idle_task_exit Woody Lin
2021-10-12 9:59 ` Valentin Schneider
2021-10-12 10:35 ` Woody Lin
2021-10-12 10:57 ` Valentin Schneider
2021-10-13 1:22 ` Woody Lin
2021-10-13 13:32 ` Valentin Schneider [this message]
2021-10-15 13:02 ` Peter Zijlstra
2021-10-19 15:23 ` [tip: sched/urgent] " tip-bot2 for Woody Lin
2021-10-19 15:55 ` tip-bot2 for Woody Lin
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