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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,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 25F05C433DB for ; Tue, 23 Mar 2021 20:43:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E5C9F619D2 for ; Tue, 23 Mar 2021 20:43:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233412AbhCWUmn (ORCPT ); Tue, 23 Mar 2021 16:42:43 -0400 Received: from ste-pvt-msa2.bahnhof.se ([213.80.101.71]:11634 "EHLO ste-pvt-msa2.bahnhof.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233637AbhCWUma (ORCPT ); Tue, 23 Mar 2021 16:42:30 -0400 Received: from localhost (localhost [127.0.0.1]) by ste-pvt-msa2.bahnhof.se (Postfix) with ESMTP id 77B923F8A2; Tue, 23 Mar 2021 21:42:24 +0100 (CET) Authentication-Results: ste-pvt-msa2.bahnhof.se; dkim=pass (1024-bit key; unprotected) header.d=shipmail.org header.i=@shipmail.org header.b=sPJS18NN; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at bahnhof.se Authentication-Results: ste-ftg-msa2.bahnhof.se (amavisd-new); dkim=pass (1024-bit key) header.d=shipmail.org Received: from ste-pvt-msa2.bahnhof.se ([127.0.0.1]) by localhost (ste-ftg-msa2.bahnhof.se [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id LggnGvMgF1Sj; Tue, 23 Mar 2021 21:42:23 +0100 (CET) Received: by ste-pvt-msa2.bahnhof.se (Postfix) with ESMTPA id 175623F700; Tue, 23 Mar 2021 21:42:21 +0100 (CET) Received: from [192.168.0.209] (unknown [192.198.151.43]) by mail1.shipmail.org (Postfix) with ESMTPSA id D723836062E; Tue, 23 Mar 2021 21:42:20 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=shipmail.org; s=mail; t=1616532141; bh=iPJ77EGHgOIrO9GhucTb28ntff/+vJnaRdy9R+OY4lo=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=sPJS18NN29rFWkVlri0remQJEnGvAMc5uNaAzOG+2DZyFbsbL6HT+f7bKV/53yxK4 WnheLIuBVVbHA0XdXpkcfyDzrml2Z5u1SRDpR8+LtCmOWIm3FfzrkjBRAo2JodoDPC 6eScF9gFQYOGN4xc1NDIGF120IZ74jlJsnN5mh2M= Subject: Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages To: "Williams, Dan J" , "dri-devel@lists.freedesktop.org" Cc: "daniel@ffwll.ch" , "christian.koenig@amd.com" , "jgg@nvidia.com" , "airlied@linux.ie" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" References: <20210321184529.59006-1-thomas_os@shipmail.org> <20210321184529.59006-2-thomas_os@shipmail.org> From: =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28Intel=29?= Message-ID: Date: Tue, 23 Mar 2021 21:42:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/23/21 8:52 PM, Williams, Dan J wrote: > On Sun, 2021-03-21 at 19:45 +0100, Thomas Hellström (Intel) wrote: >> TTM sets up huge page-table-entries both to system- and device >> memory, >> and we don't want gup to assume there are always valid backing struct >> pages for these. For PTEs this is handled by setting the pte_special >> bit, >> but for the huge PUDs and PMDs, we have neither pmd_special nor >> pud_special. Normally, huge TTM entries are identified by looking at >> vma_is_special_huge(), but fast gup can't do that, so as an >> alternative >> define _devmap entries for which there are no backing dev_pagemap as >> special, update documentation and make huge TTM entries _devmap, >> after >> verifying that there is no backing dev_pagemap. > Please do not abuse p{m,u}d_devmap like this. I'm in the process of > removing get_devpagemap() from the gup-fast path [1]. Instead there > should be space for p{m,u}d_special in the page table entries (at least > for x86-64). So the fix is to remove that old assumption that huge > pages can never be special. > > [1]: > http://lore.kernel.org/r/161604050866.1463742.7759521510383551055.stgit@dwillia2-desk3.amr.corp.intel.com > Hmm, yes with that patch it will obviously not work as intended. Given that, I think we'll need to disable the TTM huge pages for now until we can sort out and agree on using a page table entry bit. Thanks, /Thomas