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 X-Spam-Level: X-Spam-Status: No, score=-17.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D819C6369E for ; Thu, 19 Nov 2020 16:28:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 166A220757 for ; Thu, 19 Nov 2020 16:28:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="FWf3zxTk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729015AbgKSQ2b (ORCPT ); Thu, 19 Nov 2020 11:28:31 -0500 Received: from mail.kernel.org ([198.145.29.99]:44818 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728999AbgKSQ2b (ORCPT ); Thu, 19 Nov 2020 11:28:31 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8D7AB20719; Thu, 19 Nov 2020 16:28:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605803310; bh=0q3Z8JWSNAuRKy54FCbmn/BRIWds1WQi464xUGKdScs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=FWf3zxTkV6Y46boUvNDMrTMhUPO9cyUHj2FwSDBWGKPHIWJbJUH5DyeZjqi7v/b6Q tboSw+hSyfu5ZlZv/JLkz5dhjbGKDHh0mN5jw3ORPjN9J8SqTkdO4WA2ipbJQooNMK XKvYMwxgAeo1PkKg56VeWvNzYJpSz0LYXiL23spA= Date: Thu, 19 Nov 2020 16:28:23 +0000 From: Will Deacon To: Peter Zijlstra Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Morten Rasmussen , Qais Yousef , Suren Baghdasaryan , Quentin Perret , Tejun Heo , Li Zefan , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , kernel-team@android.com Subject: Re: [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Message-ID: <20201119162822.GA4582@willie-the-truck> References: <20201113093720.21106-1-will@kernel.org> <20201113093720.21106-9-will@kernel.org> <20201119161448.GR3121392@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201119161448.GR3121392@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Nov 19, 2020 at 05:14:48PM +0100, Peter Zijlstra wrote: > On Fri, Nov 13, 2020 at 09:37:13AM +0000, Will Deacon wrote: > > When exec'ing a 32-bit task on a system with mismatched support for > > 32-bit EL0, try to ensure that it starts life on a CPU that can actually > > run it. > > > > Signed-off-by: Will Deacon > > --- > > arch/arm64/kernel/process.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > index 1540ab0fbf23..17b94007fed4 100644 > > --- a/arch/arm64/kernel/process.c > > +++ b/arch/arm64/kernel/process.c > > @@ -625,6 +625,16 @@ unsigned long arch_align_stack(unsigned long sp) > > return sp & ~0xf; > > } > > > > +static void adjust_compat_task_affinity(struct task_struct *p) > > +{ > > + const struct cpumask *mask = system_32bit_el0_cpumask(); > > + > > + if (restrict_cpus_allowed_ptr(p, mask)) > > + set_cpus_allowed_ptr(p, mask); > > This silently destroys user state, at the very least that ought to go > with a WARN or something. Ideally SIGKILL though. What's to stop someone > from doing a sched_setaffinity() right after the execve, same problem. > So why bother.. It's no different to CPU hot-unplug though, is it? From the perspective of the 32-bit task, the 64-bit-only cores were hot-unplugged at the point of execve(). Calls to sched_setaffinity() for 32-bit tasks will reject attempts to include 64-bit-only cores. I initially wanted to punt this all to userspace, but one of the big problems with that is when a 64-bit task is running on a CPU only capable of running 64-bit tasks and it execve()s a 32-bit task. At the point, we have to do something because we can't even run the new task for it to do a sched_affinity() call (and we also can't deliver SIGILL). Will