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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 0C6BFC38A2A for ; Fri, 8 May 2020 20:07:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE27B24953 for ; Fri, 8 May 2020 20:06:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="Ycs8GXkC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726811AbgEHUG4 (ORCPT ); Fri, 8 May 2020 16:06:56 -0400 Received: from hqnvemgate26.nvidia.com ([216.228.121.65]:8438 "EHLO hqnvemgate26.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726767AbgEHUG4 (ORCPT ); Fri, 8 May 2020 16:06:56 -0400 Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Fri, 08 May 2020 13:06:43 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Fri, 08 May 2020 13:06:56 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 08 May 2020 13:06:56 -0700 Received: from rcampbell-dev.nvidia.com (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 8 May 2020 20:06:55 +0000 Subject: Re: [PATCH 4/6] mm/hmm: add output flag for compound page mapping To: Christoph Hellwig CC: , , , , , Jerome Glisse , "John Hubbard" , Jason Gunthorpe , "Ben Skeggs" , Andrew Morton , "Shuah Khan" , References: <20200508192009.15302-1-rcampbell@nvidia.com> <20200508192009.15302-5-rcampbell@nvidia.com> <20200508195129.GA19740@lst.de> X-Nvconfidentiality: public From: Ralph Campbell Message-ID: <1ec0511f-e6eb-3e11-ad6d-ad4e5b107464@nvidia.com> Date: Fri, 8 May 2020 13:06:55 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20200508195129.GA19740@lst.de> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1588968404; bh=1PhR0ynTTHTZ2jjSta5jo4Wils7Nsyx2BUSfOurLe2M=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=Ycs8GXkCLsC3dOjGwwVRiDFIa15xrlFp5dmFGRza+tkcfuZFMsD5xYyCaJ3SGXe5L MbsyET5GQuGbmktRrCTBcURNRpVyByNfAP6d32d3PQqHhfvXHl7hV3Vz6+jpL9f7XP CXbZOo+mS0n/H/P9XYRbSRpH1g1yZoCcRMaMatvBiqhLkjOZkUb5AO5td5VmqXKkE/ sM80B5uZfLs+ocEiGdK/OF8louCokHaVcQ5PGDdXwn/0dQA98q3hte0xdQaR0KSK8o h1YgoYDiUJdbmaXyPqLW6c0Avqm1BAzTgQczQUQuWMpS3cwZcoVq5P9xL82BMqcFaC raNhF8Jy7jtaw== Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 5/8/20 12:51 PM, Christoph Hellwig wrote: > On Fri, May 08, 2020 at 12:20:07PM -0700, Ralph Campbell wrote: >> hmm_range_fault() returns an array of page frame numbers and flags for >> how the pages are mapped in the requested process' page tables. The PFN >> can be used to get the struct page with hmm_pfn_to_page() and the page size >> order can be determined with compound_order(page) but if the page is larger >> than order 0 (PAGE_SIZE), there is no indication that the page is mapped >> using a larger page size. To be fully general, hmm_range_fault() would need >> to return the mapping size to handle cases like a 1GB compound page being >> mapped with 2MB PMD entries. However, the most common case is the mapping >> size the same as the underlying compound page size. >> Add a new output flag to indicate this so that callers know it is safe to >> use a large device page table mapping if one is available. > > Why do you need the flag? The caller should be able to just use > page_size() (or willys new thp_size helper). > The question is whether or not a large page can be mapped with smaller page table entries with different permissions. If one process has a 2MB page mapped with 4K PTEs with different read/write permissions, I don't think it would be OK for a device to map the whole 2MB with write access enabled. The flag is supposed to indicate that the whole page can be mapped by the device with the indicated read/write permissions.