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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, 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 3EFDFC6778C for ; Tue, 3 Jul 2018 17:03:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EACB620837 for ; Tue, 3 Jul 2018 17:03:14 +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="e4Pokch6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EACB620837 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934015AbeGCRDK (ORCPT ); Tue, 3 Jul 2018 13:03:10 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:49334 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932440AbeGCRDI (ORCPT ); Tue, 3 Jul 2018 13:03:08 -0400 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=WEOT40Y3+KHK/X862bVgkMG8/dkmFvOWi5Deulb3sL8=; b=e4Pokch6cr+aYAWgJODB8mg/u lBqHneE/zH5irG1jAjh07E2T+YiAPUB0HUyrWShstb2/H6nvXVt4K535DZLrE1ktZDo6ROH/N6uOu 8hfZTot2hpFwpjGEuJlr5ZBceJGELqWg7hImDYWKt5qqptvWOKGjlgdJJ61J8oDHiAPcunhpgdDGw Sr0qkwS9woUjjRO2gEoN3fCNJ/wOGOR8T8/9CY7UYsEs1hjQj6O0lhRsrb6StRqBONtTwP5+Em0Yq AT3RXkkR+aX9XelAoVeQbCLd4QFu29L3usMHKpfkK9pmcmJDf2FQkxc/W2uQSHKQGcaLAJqo/JzD+ QHTvywYog==; 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 1faOhE-0001Xz-Mf; Tue, 03 Jul 2018 17:02:32 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A0E222029764D; Tue, 3 Jul 2018 19:02:30 +0200 (CEST) Date: Tue, 3 Jul 2018 19:02:30 +0200 From: Peter Zijlstra To: Andi Kleen Cc: Heiko Carstens , Mathieu Desnoyers , Linus Torvalds , Andy Lutomirski , Thomas Gleixner , linux-kernel , linux-api , "Paul E. McKenney" , Boqun Feng , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H. Peter Anvin" , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes , michal.simek@xilinx.com, Martin Schwidefsky , Vasily Gorbik Subject: Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs Message-ID: <20180703170230.GI2458@hirez.programming.kicks-ass.net> References: <459661281.10865.1530580742205.JavaMail.zimbra@efficios.com> <858886246.10882.1530583291379.JavaMail.zimbra@efficios.com> <1776351430.10902.1530585009519.JavaMail.zimbra@efficios.com> <20180703081449.GT2494@hirez.programming.kicks-ass.net> <20180703082955.GH3704@osiris> <20180703084312.GU2494@hirez.programming.kicks-ass.net> <20180703085546.GJ3704@osiris> <20180703092113.GV2494@hirez.programming.kicks-ass.net> <20180703164048.i2te5gjemcafqzwf@two.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180703164048.i2te5gjemcafqzwf@two.firstfloor.org> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 03, 2018 at 09:40:48AM -0700, Andi Kleen wrote: > > > > So I think you're good... But yes, you raise an interresting point. > > So it sounds like architectures that don't have an instruction atomic u64 > *_user need to disable interrupts during the access, and somehow handle that > case when a page fault happens? So for 32bit, as Linus already said, a split store is _fine_, because the top word is always going to be 0 anyway. So all we really need is native word sized loads / stores. s390 is just a little weird here (it wouldn't be s390 if it wasn't I suppose) for not actually using regular loads / stores because of the split address space stuff.