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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1016CCA47E for ; Wed, 29 Jun 2022 23:06:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231181AbiF2XGL (ORCPT ); Wed, 29 Jun 2022 19:06:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229460AbiF2XGK (ORCPT ); Wed, 29 Jun 2022 19:06:10 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BEBF11DA7F; Wed, 29 Jun 2022 16:06:08 -0700 (PDT) Received: from [192.168.2.145] (109-252-118-164.nat.spd-mgts.ru [109.252.118.164]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id 97A3B660177B; Thu, 30 Jun 2022 00:06:04 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1656543967; bh=MHzNXwrpamEQJfSn517DbHauHiLavqph9+6FDdh8cW0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=R3tBCTFOx5La3aI3IuCM416s6ri/Rh+h8/CoISbxHReBFWX7oD8ghFIqxKIheLH5w K/nf9MDe20o+qs6uI9V4q7kgllcSj0UFzIr7895NwJrkgQscojZeKpuMoIZ/sXAhJ/ ByY76oOA2S/Qn7NuU44zmtC8ngpXqT/Sk6mv6EXPgD3t0Yu7tgBa91vpQ3RjptNtcQ 8wCG1+oVsnGfEAp76m0cvoIjw+tsFZcA1BMMt46ZPsluMUFRdOJVorWacWuPAU7oSR BcNWnLcHirxsy7f3PCwGEKwWPOZCORt9oP3UUBVzLpplCao7w54md/Ljni//qJgOjB FFn9vf973GUvQ== Message-ID: <467a1cee-ba8c-98f3-0398-2a7a5a90b5c3@collabora.com> Date: Thu, 30 Jun 2022 02:06:01 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v6 02/22] drm/gem: Move mapping of imported dma-bufs to drm_gem_mmap_obj() Content-Language: en-US To: =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28Intel=29?= Cc: intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, virtualization@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org, amd-gfx@lists.freedesktop.org, linux-tegra@vger.kernel.org, Dmitry Osipenko , kernel@collabora.com, linux-media@vger.kernel.org, David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Daniel Almeida , Gert Wollny , Gustavo Padovan , Daniel Stone , Tomeu Vizoso , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Rob Herring , Steven Price , Alyssa Rosenzweig , Rob Clark , Emil Velikov , Robin Murphy , Qiang Yu , Sumit Semwal , =?UTF-8?Q?Christian_K=c3=b6nig?= , "Pan, Xinhui" , Thierry Reding , Tomasz Figa , Marek Szyprowski , Mauro Carvalho Chehab , Alex Deucher , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin References: <20220526235040.678984-1-dmitry.osipenko@collabora.com> <20220526235040.678984-3-dmitry.osipenko@collabora.com> From: Dmitry Osipenko In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/29/22 11:43, Thomas Hellström (Intel) wrote: > > On 6/29/22 10:22, Dmitry Osipenko wrote: >> On 6/29/22 09:40, Thomas Hellström (Intel) wrote: >>> On 5/27/22 01:50, Dmitry Osipenko wrote: >>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't >>>> handle imported dma-bufs properly, which results in mapping of >>>> something >>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a >>>> hard >>>> lockup when userspace writes to the memory mapping of a dma-buf that >>>> was >>>> imported into Tegra's DRM GEM. >>>> >>>> To fix this bug, move mapping of imported dma-bufs to >>>> drm_gem_mmap_obj(). >>>> Now mmaping of imported dma-bufs works properly for all DRM drivers. >>> Same comment about Fixes: as in patch 1, >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Dmitry Osipenko >>>> --- >>>>    drivers/gpu/drm/drm_gem.c              | 3 +++ >>>>    drivers/gpu/drm/drm_gem_shmem_helper.c | 9 --------- >>>>    drivers/gpu/drm/tegra/gem.c            | 4 ++++ >>>>    3 files changed, 7 insertions(+), 9 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c >>>> index 86d670c71286..7c0b025508e4 100644 >>>> --- a/drivers/gpu/drm/drm_gem.c >>>> +++ b/drivers/gpu/drm/drm_gem.c >>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, >>>> unsigned long obj_size, >>>>        if (obj_size < vma->vm_end - vma->vm_start) >>>>            return -EINVAL; >>>>    +    if (obj->import_attach) >>>> +        return dma_buf_mmap(obj->dma_buf, vma, 0); >>> If we start enabling mmaping of imported dma-bufs on a majority of >>> drivers in this way, how do we ensure that user-space is not blindly >>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC >>> which is needed before and after cpu access of mmap'ed dma-bufs? >>> >>> I was under the impression (admittedly without looking) that the few >>> drivers that actually called into dma_buf_mmap() had some private >>> user-mode driver code in place that ensured this happened. >> Since it's a userspace who does the mapping, then it should be a >> responsibility of userspace to do all the necessary syncing. > > Sure, but nothing prohibits user-space to ignore the syncing thinking > "It works anyway", testing those drivers where the syncing is a NOP. And > when a driver that finally needs syncing is tested it's too late to fix > all broken user-space. > >>   I'm not >> sure whether anyone in userspace really needs to map imported dma-bufs >> in practice. Nevertheless, this use-case is broken and should be fixed >> by either allowing to do the mapping or prohibiting it. >> > Then I'd vote for prohibiting it, at least for now. And for the future > moving forward we could perhaps revisit the dma-buf need for syncing, > requiring those drivers that actually need it to implement emulated > coherent memory which can be done not too inefficiently (vmwgfx being > one example). Alright, I'll change it to prohibit the mapping. This indeed should be a better option. -- Best regards, Dmitry