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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1A33DC433DF for ; Fri, 10 Jul 2020 09:42:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E5690206F4 for ; Fri, 10 Jul 2020 09:42:18 +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="zA0m11Wb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726867AbgGJJmR (ORCPT ); Fri, 10 Jul 2020 05:42:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55884 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726560AbgGJJmR (ORCPT ); Fri, 10 Jul 2020 05:42:17 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E930BC08C5CE; Fri, 10 Jul 2020 02:42:16 -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=ZjyAASXArgWq7Bdptru/76m4wkYaBPhc/UpB8fdqxik=; b=zA0m11Wbj0k3n0yOG9UmwXpKUJ V17bvo/1zKlsCPwQNKiZI/RjBUNXZkUNWu9dvgin0QAOptrpEHiKCR4/IpSlfVuUvwky/9TEbfIqF o9/aLWSBXIFmpR9byGbnDCEeW84gtfWVMHMKx9HA7wmjEzghv5VZAOE6heMECAbZjly10rSBK4Rw/ xx11ZaN+4V9LRQu7I55jib6FRuZ7VBF4mmzoR0vHkKzdNQGxcdLJ8Vynn4NPnLiXRk2znsjGK50BT pB7+kPXU0eTO3snr3WCNcbkhlk7YwAm86/gqK+Z8pClP1S14vHWsZCaxWzQpLVs3JP2meGj2CuWD6 d+9rH4iQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jtpXf-0003av-46; Fri, 10 Jul 2020 09:42:03 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id A8922301179; Fri, 10 Jul 2020 11:42:01 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 944062B5130F2; Fri, 10 Jul 2020 11:42:01 +0200 (CEST) Date: Fri, 10 Jul 2020 11:42:01 +0200 From: Peter Zijlstra To: Nicholas Piggin Cc: linux-arch@vger.kernel.org, x86@kernel.org, Mathieu Desnoyers , Arnd Bergmann , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, Anton Blanchard Subject: Re: [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before_usermode Message-ID: <20200710094201.GZ4800@hirez.programming.kicks-ass.net> References: <20200710015646.2020871-1-npiggin@gmail.com> <20200710015646.2020871-5-npiggin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200710015646.2020871-5-npiggin@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 10, 2020 at 11:56:43AM +1000, Nicholas Piggin wrote: > And get rid of the generic sync_core_before_usermode facility. > > This helper is the wrong way around I think. The idea that membarrier > state requires a core sync before returning to user is the easy one > that does not need hiding behind membarrier calls. The gap in core > synchronization due to x86's sysret/sysexit and lazy tlb mode, is the > tricky detail that is better put in x86 lazy tlb code. > > Consider if an arch did not synchronize core in switch_mm either, then > membarrier_mm_sync_core_before_usermode would be in the wrong place > but arch specific mmu context functions would still be the right place. > There is also a exit_lazy_tlb case that is not covered by this call, which > could be a bugs (kthread use mm the membarrier process's mm then context > switch back to the process without switching mm or lazy mm switch). > > This makes lazy tlb code a bit more modular. Hurmph, I know I've been staring at this at some point. I think I meant to have a TIF to force the IRET path in the case of MEMBAR_SYNC_CORE. But I was discouraged by amluto.