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,URIBL_BLOCKED, 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 B1C7EC282CA for ; Wed, 13 Feb 2019 14:25:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 80E47222B2 for ; Wed, 13 Feb 2019 14:25:30 +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="V4ZG+dan" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392138AbfBMOZ3 (ORCPT ); Wed, 13 Feb 2019 09:25:29 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:59304 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731144AbfBMOZ2 (ORCPT ); Wed, 13 Feb 2019 09:25:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=BUSZJBEg95AZWRLllyUlX+QB7MyHQPRRcdezTH5hoC0=; b=V4ZG+danGvaZXWrUGwCSf80h0 BfIFH9QB1K2fXBwyb0rx6rBXssH3T4qBVLC0KWosOX3xWw6+DV2mf5g1+hLpznzR+SF+KUoIss0XT tBu1F5wFqiyCBzvJS7di1WV5K/L8pr+sTF5/QgcPkIYxlx4g91tGoLSOSdUlkb806tnsPRYhDJxRU TVaLPA1gbBKPedf/qa89TuJYG8Q3R+Kl0ioncTrIYAjZLAHNTOMuovabtU6heLKz0S6/yRbXXgPVk gL9bO1Di7u2IRjXSyQd8Fmsffg8kJS8RCeoakXwImDD2SXQINGdv4pd26+Oy15WwISx5i0FrmN5pO jJ3B9V7Cg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtvTZ-0002Qt-Ty; Wed, 13 Feb 2019 14:25:26 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 24EDB20F51B0C; Wed, 13 Feb 2019 15:25:24 +0100 (CET) Date: Wed, 13 Feb 2019 15:25:24 +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: <20190213142524.GW32494@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: > 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. A quick reading of the SDM seems to suggest the SMAP state is part of EFLAGS, which is context switched just fine AFAIK. SMAP {ab,re}uses the EFLAGS.AC bit. > 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.