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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 2C569C4361B for ; Fri, 18 Dec 2020 18:58:25 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6FEC523B85 for ; Fri, 18 Dec 2020 18:58:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6FEC523B85 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9F61B6B005D; Fri, 18 Dec 2020 13:58:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9A68A6B0068; Fri, 18 Dec 2020 13:58:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8E42B6B006C; Fri, 18 Dec 2020 13:58:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0183.hostedemail.com [216.40.44.183]) by kanga.kvack.org (Postfix) with ESMTP id 788FF6B005D for ; Fri, 18 Dec 2020 13:58:23 -0500 (EST) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 3B000612D for ; Fri, 18 Dec 2020 18:58:23 +0000 (UTC) X-FDA: 77607313686.14.dust22_13183c82743f Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin14.hostedemail.com (Postfix) with ESMTP id 1446618229835 for ; Fri, 18 Dec 2020 18:58:23 +0000 (UTC) X-HE-Tag: dust22_13183c82743f X-Filterd-Recvd-Size: 2317 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf19.hostedemail.com (Postfix) with ESMTP for ; Fri, 18 Dec 2020 18:58:22 +0000 (UTC) Date: Fri, 18 Dec 2020 10:58:20 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1608317901; bh=VB8+n3UKNHQUY5lgxzqwpG48dgmXNMTEQW51p6dUcfw=; h=From:To:Cc:Subject:In-Reply-To:References:From; b=152tFpXJQGA0h5QNO00MariTRPlm/M+SZbu09C7qH0rjEEd27/jglH59DciGGeIxR 59+2jebeQccNbDVKk/yLcs3W4ReaHAR7zbp3Iuh7NlKFxq9gwKOSrMHrlumpOGUTTx dglWD2Q7tSvnskHEHXoibXsiakhkos+GEAQKlHCQ= From: Andrew Morton To: Nicholas Piggin Cc: linux-mm@kvack.org, Suresh Siddha , "David S. Miller" , Hugh Dickins , Peter Zijlstra , Suresh Siddha , Linus Torvalds Subject: Re: [RFC PATCH] mm: generalise COW SMC TLB flushing race comment Message-Id: <20201218105820.1806d97ae37db3b93cb8192d@linux-foundation.org> In-Reply-To: <20201215121119.351650-1-npiggin@gmail.com> References: <20201215121119.351650-1-npiggin@gmail.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 15 Dec 2020 22:11:19 +1000 Nicholas Piggin wrote: > I'm not sure if I'm completely missing something here, but AFAIKS the > reference to the mysterious "COW SMC race" confuses the issue. The original > changelog and mailing list thread didn't help me either. > > This SMC race is where the problem was detected, but isn't the general > problem bigger and more obvious: that the new PTE could be picked > up at any time by any TLB while entries for the old PTE exist in other > TLBs before the TLB flush takes effect? > > The case where the iTLB and dTLB of a CPU are pointing at different > pages is an interesting one but follows from the general problem. > > The other (minor) thing with the comment I think it makes it a bit > clearer to say what the old code was doing (i.e., it avoids the race > as opposed to what?). Could we please have a signed-off-by for this?