From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 91531C433F5 for ; Wed, 13 Oct 2021 13:33:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 713CA60F11 for ; Wed, 13 Oct 2021 13:33:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234356AbhJMNfD (ORCPT ); Wed, 13 Oct 2021 09:35:03 -0400 Received: from foss.arm.com ([217.140.110.172]:39328 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229535AbhJMNfB (ORCPT ); Wed, 13 Oct 2021 09:35:01 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8F3B31FB; Wed, 13 Oct 2021 06:32:58 -0700 (PDT) Received: from e113632-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 222203F66F; Wed, 13 Oct 2021 06:32:57 -0700 (PDT) From: Valentin Schneider To: Woody Lin Cc: Ingo Molnar , Ben Segall , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Mel Gorman , Daniel Bristot de Oliveira , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/scs: Reset the shadow stack when idle_task_exit In-Reply-To: References: <20211012083521.973587-1-woodylin@google.com> <87zgrek1gl.mognet@arm.com> <87wnmijysj.mognet@arm.com> Date: Wed, 13 Oct 2021 14:32:51 +0100 Message-ID: <87tuhljbi4.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/10/21 09:22, Woody Lin wrote: > On Tue, Oct 12, 2021 at 6:57 PM Valentin Schneider 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 > Regards, > Woody > >> >> >> >> >> > } >> >> > >> >> > -- >> >> > 2.33.0.882.g93a45727a2-goog