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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 A8794C2BC73 for ; Wed, 4 Dec 2019 14:16:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7F6FA20674 for ; Wed, 4 Dec 2019 14:16:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=shipmail.org header.i=@shipmail.org header.b="rZAHpK0e" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727972AbfLDOQT (ORCPT ); Wed, 4 Dec 2019 09:16:19 -0500 Received: from pio-pvt-msa2.bahnhof.se ([79.136.2.41]:39368 "EHLO pio-pvt-msa2.bahnhof.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727792AbfLDOQT (ORCPT ); Wed, 4 Dec 2019 09:16:19 -0500 Received: from localhost (localhost [127.0.0.1]) by pio-pvt-msa2.bahnhof.se (Postfix) with ESMTP id 404F63F47A; Wed, 4 Dec 2019 15:16:16 +0100 (CET) Authentication-Results: pio-pvt-msa2.bahnhof.se; dkim=pass (1024-bit key; unprotected) header.d=shipmail.org header.i=@shipmail.org header.b=rZAHpK0e; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at bahnhof.se Received: from pio-pvt-msa2.bahnhof.se ([127.0.0.1]) by localhost (pio-pvt-msa2.bahnhof.se [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Km9YbJabySxh; Wed, 4 Dec 2019 15:16:15 +0100 (CET) Received: from mail1.shipmail.org (h-205-35.A357.priv.bahnhof.se [155.4.205.35]) (Authenticated sender: mb878879) by pio-pvt-msa2.bahnhof.se (Postfix) with ESMTPA id B12EC3F435; Wed, 4 Dec 2019 15:16:10 +0100 (CET) Received: from localhost.localdomain (h-205-35.A357.priv.bahnhof.se [155.4.205.35]) by mail1.shipmail.org (Postfix) with ESMTPSA id CC96A360608; Wed, 4 Dec 2019 15:16:09 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=shipmail.org; s=mail; t=1575468969; bh=6lPiouUhoiffGwUD7wWb3htpX7yUG7AcztUp9kFYLLI=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=rZAHpK0eBRbwsu388vybVwAbkZPQbHLOKHyty+7r1UkSH/04RpXI227bMqMFVxlRP UrWX6Ijp3UQj9Wj1JrcokDlB6PmEsywz/A8GWJ0k+N90X8OolmzmVQX97MzB97QuBG Cuz7tDkgVF3SLv9OwcbU14195XaWJKO0qK8uDafY= Subject: Re: [PATCH v2 2/2] drm/ttm: Fix vm page protection handling To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, pv-drivers@vmware.com, linux-graphics-maintainer@vmware.com, Thomas Hellstrom , Andrew Morton , "Matthew Wilcox (Oracle)" , "Kirill A. Shutemov" , Ralph Campbell , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20191203104853.4378-1-thomas_os@shipmail.org> <20191203104853.4378-3-thomas_os@shipmail.org> <20191204135219.GH25242@dhcp22.suse.cz> From: =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28VMware=29?= Organization: VMware Inc. Message-ID: Date: Wed, 4 Dec 2019 15:16:09 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20191204135219.GH25242@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/4/19 2:52 PM, Michal Hocko wrote: > On Tue 03-12-19 11:48:53, Thomas Hellström (VMware) wrote: >> From: Thomas Hellstrom >> >> TTM graphics buffer objects may, transparently to user-space, move >> between IO and system memory. When that happens, all PTEs pointing to the >> old location are zapped before the move and then faulted in again if >> needed. When that happens, the page protection caching mode- and >> encryption bits may change and be different from those of >> struct vm_area_struct::vm_page_prot. >> >> We were using an ugly hack to set the page protection correctly. >> Fix that and instead use vmf_insert_mixed_prot() and / or >> vmf_insert_pfn_prot(). >> Also get the default page protection from >> struct vm_area_struct::vm_page_prot rather than using vm_get_page_prot(). >> This way we catch modifications done by the vm system for drivers that >> want write-notification. > So essentially this should have any new side effect on functionality it > is just making a hacky/ugly code less so? Functionality is unchanged. The use of a on-stack vma copy was severely frowned upon in an earlier thread, which also points to another similar example using vmf_insert_pfn_prot(). https://lore.kernel.org/lkml/20190905103541.4161-2-thomas_os@shipmail.org/ > In other words what are the > consequences of having page protection inconsistent from vma's? During the years, it looks like the caching- and encryption flags of vma::vm_page_prot have been largely removed from usage. From what I can tell, there are no more places left that can affect TTM. We discussed __split_huge_pmd_locked() towards the end of that thread, but that doesn't affect TTM even with huge page-table entries. /Thomas