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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 D4FBCC43387 for ; Fri, 4 Jan 2019 17:42:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A7200218CD for ; Fri, 4 Jan 2019 17:42:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="b9PjUlbt"; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="IJR+G2sI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728300AbfADRmF (ORCPT ); Fri, 4 Jan 2019 12:42:05 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:39058 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727127AbfADRmF (ORCPT ); Fri, 4 Jan 2019 12:42:05 -0500 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 323D4608C6; Fri, 4 Jan 2019 17:42:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1546623723; bh=zca2SsK3nw3O37+eqanDCtOSt04ycSV0pycfbAUlwnI=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=b9PjUlbtJ2QlUpybN3OBem5d0O9WUYXMoSAXC7N3zW0aG8y8p0QvKPdG0sjPvDZuZ 6DvTTFDO60kawEQT5yizdZ2UMpxQo/Se15zytYP1BWBEZ9ypfz6bTKIArK6Iy4QlDT MWvPfUkzxZH+bTe73cwoD4ODg1Mq7in4blGePNz4= Received: from lmark-linux.qualcomm.com (i-global254.qualcomm.com [199.106.103.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: lmark@smtp.codeaurora.org) by smtp.codeaurora.org (Postfix) with ESMTPSA id 98AED6087F; Fri, 4 Jan 2019 17:41:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1546623719; bh=zca2SsK3nw3O37+eqanDCtOSt04ycSV0pycfbAUlwnI=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=IJR+G2sINhxdvmzAbMxLh5+weluEm2lBDAh1E/lf9Nn1mcd4eG2m6y4CE7CbY3COG iWM2tFd6tSd5LR2uu3JkcFczsFHpZY87BjkOYjPQBmk8x3k85PkDM92RBgfKwcZjtU RLtUdx+niAyuKkPHzkKKoK3eK5XYvWlQ19Uhc42M= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 98AED6087F Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=lmark@codeaurora.org Date: Fri, 4 Jan 2019 09:41:57 -0800 (PST) From: Liam Mark X-X-Sender: lmark@lmark-linux.qualcomm.com To: Alexey Skidanov cc: Laura Abbott , Greg KH , devel@driverdev.osuosl.org, tkjos@android.com, rve@android.com, linux-kernel@vger.kernel.org, maco@android.com, sumit.semwal@linaro.org Subject: Re: [PATCH v3] staging: android: ion: Add implementation of dma_buf_vmap and dma_buf_vunmap In-Reply-To: <3740948f-02be-cf7a-bc41-54b4fd195103@intel.com> Message-ID: References: <1517400222-2854-1-git-send-email-alexey.skidanov@intel.com> <20180131130047.GA22917@kroah.com> <89be45dd-ac0e-4efb-2b21-e6c07b0cd66e@intel.com> <7d836085-cd8d-300b-56be-e8db4ff37afc@intel.com> <67f288db-d9ea-2d45-ddcf-a15dbff316f5@intel.com> <3740948f-02be-cf7a-bc41-54b4fd195103@intel.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 Dec 2018, Alexey Skidanov wrote: > >>> I was wondering if we could re-open the discussion on adding support to > >>> ION for dma_buf_vmap. > >>> It seems like the patch was not taken as the reviewers wanted more > >>> evidence of an upstream use case. > >>> > >>> Here would be my upstream usage argument for including dma_buf_vmap > >>> support in ION. > >>> > >>> Currently all calls to ion_dma_buf_begin_cpu_access result in the creation > >>> of a kernel mapping for the buffer, unfortunately the resulting call to > >>> alloc_vmap_area can be quite expensive and this has caused a performance > >>> regression for certain clients when they have moved to the new version of > >>> ION. > >>> > >>> The kernel mapping is not actually needed in ion_dma_buf_begin_cpu_access, > >>> and generally isn't needed by clients. So if we remove the creation of the > >>> kernel mapping in ion_dma_buf_begin_cpu_access and only create it when > >>> needed we can speed up the calls to ion_dma_buf_begin_cpu_access. > >>> > >>> An additional benefit of removing the creation of kernel mappings from > >>> ion_dma_buf_begin_cpu_access is that it makes the ION code more secure. > >>> Currently a malicious client could call the DMA_BUF_IOCTL_SYNC IOCTL with > >>> flags DMA_BUF_SYNC_END multiple times to cause the ION buffer kmap_cnt to > >>> go negative which could lead to undesired behavior. > >>> > >>> One disadvantage of the above change is that a kernel mapping is not > >>> already created when a client calls dma_buf_kmap. So the following > >>> dma_buf_kmap contract can't be satisfied. > >>> > >>> /** > >>> * dma_buf_kmap - Map a page of the buffer object into kernel address > >>> space. The > >>> * same restrictions as for kmap and friends apply. > >>> * @dmabuf: [in] buffer to map page from. > >>> * @page_num: [in] page in PAGE_SIZE units to map. > >>> * > >>> * This call must always succeed, any necessary preparations that might > >>> fail > >>> * need to be done in begin_cpu_access. > >>> */ > >>> > >>> But hopefully we can work around this by moving clients to dma_buf_vmap. > >> I think the problem is with the contract. We can't ensure that the call > >> is always succeeds regardless the implementation - any mapping might > >> fail. Probably this is why *all* clients of dma_buf_kmap() check the > >> return value (so it's safe to return NULL in case of failure). > >> > > > > I think currently the call to dma_buf_kmap will always succeed since the > > DMA-Buf contract requires that the client first successfully call > > dma_buf_begin_cpu_access(), and if dma_buf_begin_cpu_access() succeeds > > then dma_buf_kmap will succeed. > > > >> I would suggest to fix the contract and to keep the dma_buf_kmap() > >> support in ION. > > > > I will leave it to the DMA-Buf maintainers as to whether they want to > > change their contract. > > > > Liam > > > > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > > a Linux Foundation Collaborative Project > > > > Ok. We need the list of the clients using the ION in the mainline tree. > Looks to me like the only functions which might be calling dma_buf_kmap/dma_buf_kunmap on ION buffers are tegra_bo_kmap/tegra_bo_kunmap, I assume Tegra is used in some Android automotive products. Looks like these functions could be moved over to using dma_buf_vmap/dma_buf_vunmap but it wouldn't be very clean and would add a performance hit. Liam Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project