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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 8AEA9C43467 for ; Wed, 14 Oct 2020 15:45:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EA36C22254 for ; Wed, 14 Oct 2020 15:45:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="nTgLQYcN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EA36C22254 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 01110900002; Wed, 14 Oct 2020 11:45:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EDAD96B0071; Wed, 14 Oct 2020 11:45:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D55B9900002; Wed, 14 Oct 2020 11:45:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0008.hostedemail.com [216.40.44.8]) by kanga.kvack.org (Postfix) with ESMTP id 9DA986B0070 for ; Wed, 14 Oct 2020 11:45:53 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 29B521EE6 for ; Wed, 14 Oct 2020 15:45:53 +0000 (UTC) X-FDA: 77370956586.21.toe44_2f10b862720d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id F1EE3180442C2 for ; Wed, 14 Oct 2020 15:45:52 +0000 (UTC) X-HE-Tag: toe44_2f10b862720d X-Filterd-Recvd-Size: 3625 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf43.hostedemail.com (Postfix) with ESMTP for ; Wed, 14 Oct 2020 15:45:52 +0000 (UTC) Received: from mail-wr1-f43.google.com (mail-wr1-f43.google.com [209.85.221.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 204CD2222C for ; Wed, 14 Oct 2020 15:45:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602690351; bh=9lOn7d49hdMJPBAKNJlKjJFXwOCSJN+nr4aroBt0z8Q=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=nTgLQYcNgiV4xvOcNFfqLSyoduB9LQwUmo1XmTF09eY04eNM9AZqsq/rx1nPTEgXD 0iuygi538DbVwzDItQUCEkVx9WpDUcIaZ4JnnDqp3LPu5Moe5o9SgIRXCOdoE+kwVc NbH+N+n9MrrXEuLLWikuOiwUuZjfMiIt+mAlH0BI= Received: by mail-wr1-f43.google.com with SMTP id h7so4473444wre.4 for ; Wed, 14 Oct 2020 08:45:51 -0700 (PDT) X-Gm-Message-State: AOAM533LrK3Kf2OtJyp7ATeNcruW9q1sz16JnSn5J+Q2mHJsGUlcYND9 iFQjzpskix4Klf5CGbnOAnAXRHAcwV1oxUe4mDorxQ== X-Google-Smtp-Source: ABdhPJzQOydMjXK4UiJ3SXU5rT4smyYe2CcWv5kxCt2+PoOm7xJWs7FQA9thboa3WyHRS1tM8wCbwVh1dzX3hQW3mXI= X-Received: by 2002:a5d:6744:: with SMTP id l4mr6472625wrw.18.1602690349612; Wed, 14 Oct 2020 08:45:49 -0700 (PDT) MIME-Version: 1.0 References: <20201014083300.19077-1-ankur.a.arora@oracle.com> <20201014083300.19077-6-ankur.a.arora@oracle.com> In-Reply-To: <20201014083300.19077-6-ankur.a.arora@oracle.com> From: Andy Lutomirski Date: Wed, 14 Oct 2020 08:45:37 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 5/8] x86/clear_page: add clear_page_uncached() To: Ankur Arora Cc: LKML , Linux-MM , "Kirill A. Shutemov" , Michal Hocko , Boris Ostrovsky , Konrad Rzeszutek Wilk , Thomas Gleixner , Ingo Molnar , Borislav Petkov , X86 ML , "H. Peter Anvin" , Arnd Bergmann , Andrew Morton , Ira Weiny , linux-arch Content-Type: text/plain; charset="UTF-8" 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 Wed, Oct 14, 2020 at 1:33 AM Ankur Arora wrote: > > Define clear_page_uncached() as an alternative_call() to clear_page_nt() > if the CPU sets X86_FEATURE_NT_GOOD and fallback to clear_page() if it > doesn't. > > Similarly define clear_page_uncached_flush() which provides an SFENCE > if the CPU sets X86_FEATURE_NT_GOOD. As long as you keep "NT" or "MOVNTI" in the names and keep functions in arch/x86, I think it's reasonable to expect that callers understand that MOVNTI has bizarre memory ordering rules. But once you give something a generic name like "clear_page_uncached" and stick it in generic code, I think the semantics should be more obvious. How about: clear_page_uncached_unordered() or clear_page_uncached_incoherent() and flush_after_clear_page_uncached() After all, a naive reader might expect "uncached" to imply "caches are off and this is coherent with everything". And the results of getting this wrong will be subtle and possibly hard-to-reproduce corruption. --Andy