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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 3C234C282C2 for ; Wed, 13 Feb 2019 14:17:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9DA1C222B5 for ; Wed, 13 Feb 2019 14:17:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="nANY/kzs" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731832AbfBMORV (ORCPT ); Wed, 13 Feb 2019 09:17:21 -0500 Received: from merlin.infradead.org ([205.233.59.134]:43938 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726654AbfBMORV (ORCPT ); Wed, 13 Feb 2019 09:17:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=g/rY88dwSNgbI6IugayxPvzdNhP0vcbds2CwH0My2R8=; b=nANY/kzsxnA2sMgFWRcxl84RF n7xpk9vO/3NldWgY6XbNt8qNpFT8U9qnKo/hD3V2vL++wJsjG1mTc2ZFsOI73xnvi7tMJgw0acaXn N+xjP/EJSRPnpP3eVbEAvRWvvotZ/hnKgZdo8M9HofQY9pZJcxZaK63Pm/WIrIi8Q0jMU3eIN4Rco EhkwKvV3rdI0Ha7Jd7N7VbmS6oC3VwRqFzJDNH/mbbfTy9I4oZXrIXFuLK5//zxw5eEjQjm9RjT5F WNYOAO4dm6SFvdjr72bsQJc0LLxQIki3QARfvTaTWx5fnq6XBAkiB7ft4khObn2FIlJfXWKpx6Xcr obAwfKlkA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtvLf-00012z-Vt; Wed, 13 Feb 2019 14:17:16 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E50C520F51B0C; Wed, 13 Feb 2019 15:17:12 +0100 (CET) Date: Wed, 13 Feb 2019 15:17:12 +0100 From: Peter Zijlstra To: Will Deacon Cc: Julien Thierry , Ingo Molnar , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, mingo@redhat.com, catalin.marinas@arm.com, james.morse@arm.com, hpa@zytor.com, valentin.schneider@arm.com Subject: Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region Message-ID: <20190213141712.GV32494@hirez.programming.kicks-ass.net> References: <1547560709-56207-1-git-send-email-julien.thierry@arm.com> <1547560709-56207-4-git-send-email-julien.thierry@arm.com> <20190211134527.GA121589@gmail.com> <20190211135159.GC32511@hirez.programming.kicks-ass.net> <20190213103553.GO32494@hirez.programming.kicks-ass.net> <1c2429a4-9df9-40a3-98e0-51577de4bd6a@arm.com> <20190213131720.GU32494@hirez.programming.kicks-ass.net> <20190213140025.GB6346@brain-police> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190213140025.GB6346@brain-police> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 13, 2019 at 02:00:26PM +0000, Will Deacon wrote: > > This; how is getting preempted fundamentally different from scheduling > > ourselves? > > The difference is because getting preempted in the sequence above is > triggered off the back of an interrupt. On arm64, and I think also on x86, > the user access state (SMAP or PAN) is saved and restored across exceptions > but not across context switch. Consequently, taking an irq in a > user_access_{begin,end} section and then scheduling is fine, but calling > schedule directly within such a section is not. So how's this then: if (user_access_begin()) { preempt_disable(); set_need_resched(); preempt_enable() __schedule(); user_access_end(); } That _should_ work just fine but explodes with the proposed nonsense.