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=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,UPPERCASE_50_75,USER_AGENT_SANE_1 autolearn=no 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 C74BAC433DF for ; Tue, 11 Aug 2020 07:54:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9EE6220658 for ; Tue, 11 Aug 2020 07:54:33 +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="0i0sScr/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728178AbgHKHyc (ORCPT ); Tue, 11 Aug 2020 03:54:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46528 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728133AbgHKHyc (ORCPT ); Tue, 11 Aug 2020 03:54:32 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D7C88C061787 for ; Tue, 11 Aug 2020 00:54:31 -0700 (PDT) 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; bh=BJ6NngLNkSYp1sT0N1/N2C51huBBRbAX2VjGCXSkBSg=; b=0i0sScr/Cr7h1kkBEKTDu101YF qtTsZ2DEO1xzwMWXsvaJAH7bq3GzL2PmLIge+QKKoAfGVDsMrAsPitjkPH9vUBvFFXshSHlkROMOD FoFlSItG/vqJBs/HcY2qMTDQZ+Cgtu0eRebEHbrJnpYlRErTnocI0fuPgVcKJVGCYSAslQcv4t2tF 10upX3tTokJhm0n8kVHY+0F05ZsLkzNH+7P62RpTeN8K7m6+CrVdh+LlHny+BQUmZSkn57NtVyzHV e/QNH5AfOmd29El/b5rcKAZeAs2WHRtj33PEltpe6yRAO/y2BqaXUUszut+gBpThSosIoMWcVJ46l GTVwEHfw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k5P70-000204-6o; Tue, 11 Aug 2020 07:54:22 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 8D56D980C9D; Tue, 11 Aug 2020 09:54:20 +0200 (CEST) Date: Tue, 11 Aug 2020 09:54:20 +0200 From: Peter Zijlstra To: Peter Oskolkov Cc: Mathieu Desnoyers , "Paul E . McKenney" , Boqun Feng , linux-kernel@vger.kernel.org, Paul Turner , Chris Kennelly , Peter Oskolkov Subject: Re: [PATCH 1/2 v3] rseq/membarrier: add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ Message-ID: <20200811075420.GA5637@worktop.programming.kicks-ass.net> References: <20200811000959.2486636-1-posk@google.com> <20200811062733.GP3982@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200811062733.GP3982@worktop.programming.kicks-ass.net> 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 Tue, Aug 11, 2020 at 08:27:33AM +0200, Peter Zijlstra wrote: > SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) > { > + int cflags = 0, int cpuid = -1; > + > if (unlikely(flags) && cmd != MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ) > return -EINVAL; > + > + if (cmd & (MEMBARRIER_CMD_PRIVATE_EXPEDITED | > + MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE | > + MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ)) { > + > + if (cmd & MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ) > + cflags |= MEMBARRIER_FLAG_RSEQ; > + > + if (cmd & MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE) { > + cflags |= MEMBARRIER_FLAG_SYNC_CORE; > + cpuid = flags; > + } > + > + cmd = MEMBARRIER_CMD_PRIVATE_EXPEDITED; > + } This of course fails to check if other bits are set, and it goes really 'funny' if you use cpuid != -1. That all needs a little more thought.