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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 77329C433E6 for ; Thu, 14 Jan 2021 09:24:16 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0917723A05 for ; Thu, 14 Jan 2021 09:24:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0917723A05 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=chris-wilson.co.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6512F6E0F7; Thu, 14 Jan 2021 09:24:13 +0000 (UTC) Received: from fireflyinternet.com (unknown [77.68.26.236]) by gabe.freedesktop.org (Postfix) with ESMTPS id 42D9289FF7; Thu, 14 Jan 2021 09:24:10 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from localhost (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP (TLS) id 23592012-1500050 for multiple; Thu, 14 Jan 2021 09:23:20 +0000 MIME-Version: 1.0 In-Reply-To: References: <20210113140604.3615437-1-daniel.vetter@ffwll.ch> <161055261490.6195.7986280621869334351@build.alporthouse.com> <161057213487.6195.581396740566956696@build.alporthouse.com> Subject: Re: [Intel-gfx] [PATCH] drm-buf: Add debug option From: Chris Wilson To: Daniel Vetter , John Stultz Date: Thu, 14 Jan 2021 09:23:18 +0000 Message-ID: <161061619887.19482.10606780107376365239@build.alporthouse.com> User-Agent: alot/0.9 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Intel Graphics Development , DRI Development , linux-media@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Quoting Daniel Vetter (2021-01-14 09:02:57) > On Wed, Jan 13, 2021 at 10:08 PM Chris Wilson wrote: > > Quoting Daniel Vetter (2021-01-13 20:50:11) > > > On Wed, Jan 13, 2021 at 4:43 PM Chris Wilson wrote: > > > > > > > > Quoting Daniel Vetter (2021-01-13 14:06:04) > > > > > We have too many people abusing the struct page they can get at but > > > > > really shouldn't in importers. Aside from that the backing page might > > > > > simply not exist (for dynamic p2p mappings) looking at it and using it > > > > > e.g. for mmap can also wreak the page handling of the exporter > > > > > completely. Importers really must go through the proper interface like > > > > > dma_buf_mmap for everything. > > > > > > > > If the exporter doesn't want to expose the struct page, why are they > > > > setting it in the exported sg_table? > > > > > > You need to store it somewhere, otherwise the dma-api doesn't work. > > > Essentially this achieves clearing/resetting the struct page pointer, > > > without additional allocations somewhere, or tons of driver changes > > > (since presumably the driver does keep track of the struct page > > > somewhere too). > > > > Only for mapping, and that's before the export -- if there's even a > > struct page to begin with. > > > > > Also as long as we have random importers looking at struct page we > > > can't just remove it, or crashes everywhere. So it has to be some > > > debug option you can disable. > > > > Totally agreed that nothing generic can rely on pages being transported > > via dma-buf, and memfd is there if you do want a suitable transport. The > > one I don't know about is dma-buf heap, do both parties there consent to > > transport pages via the dma-buf? i.e. do they have special cases for > > import/export between heaps? > > heaps shouldn't be any different wrt the interface exposed to > importers. Adding John just in case I missed something. > > I think the only problem we have is that the first import for ttm > simply pulled out the struct page and ignored the sgtable otherwise, > then that copypasted to places and we're still have some of that left. > Although it's a lot better. So largely the problem is importers being > a bit silly. > > I also think I should change the defaulty y to default y if > DMA_API_DEBUG or something like that, to make sure it's actually > enabled often enough. It felt overly draconian, but other than the open question of dma-buf heaps (which I realise that we need some CI coverage for), I can't think of a good reason to argue for hiding a struct page transport within dma-buf. The only other problem I see with the implementation is that there's nothing that says that each dmabuf->ops->map_dma_buf() returns a new sg_table, so we may end up undoing the xor. Or should each dma-buf return a fresh dma-mapping for iommu isolation? -Chris _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel