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 B17ADC25B07 for ; Wed, 10 Aug 2022 22:23:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233403AbiHJWXt (ORCPT ); Wed, 10 Aug 2022 18:23:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231508AbiHJWXq (ORCPT ); Wed, 10 Aug 2022 18:23:46 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 018048C47A; Wed, 10 Aug 2022 15:23:44 -0700 (PDT) Received: from [192.168.2.145] (109-252-119-13.nat.spd-mgts.ru [109.252.119.13]) (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 C557D6601C72; Wed, 10 Aug 2022 23:23:41 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1660170223; bh=pAn4Gqp6D8HcRM++p5rp1zp4bx+HGH72YfOrKPVutak=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Hy6NwvWzvecyL1fNE9R5xtY630z1HmVBGl3iuQqiVuNBfJL0+0VcZKnZzle6iq9zO TxF3zQ/l2CP2UkSffjSsNabEnA+jMXpN8wuw0/hJR2UfPqzC86GE3cntMVPo1dB+bY R4F30grLWmoP9XuEm4RplG9QDUiUHgH89lqhk5p30kG1UpPNIONzXFfTH60volBVqm YLNQFLrAvePwQsN5RbrOatLximRMd5AbWq8Er52vIO8XvWsg8jKQ0FtJDQZ8pKsDZ+ xpsTHVbbmXE8aJOvBnfOQql/CPGjgZiu49UK3PBOlkTTC9pVTKl0tSEjTscPprx2FK k7f7d1npbko0Q== Message-ID: Date: Thu, 11 Aug 2022 01:23:39 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v8 2/2] drm/gem: Don't map imported GEMs Content-Language: en-US To: Rob Clark Cc: =?UTF-8?Q?Christian_K=c3=b6nig?= , David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Emil Velikov , =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= , Linux Kernel Mailing List , dri-devel , "open list:VIRTIO GPU DRIVER" , linux-tegra@vger.kernel.org, Dmitry Osipenko , kernel@collabora.com, Daniel Vetter References: <20220701090240.1896131-1-dmitry.osipenko@collabora.com> <20220701090240.1896131-3-dmitry.osipenko@collabora.com> <2bb95e80-b60a-36c0-76c8-a06833032c77@amd.com> <2a646ce4-c2ec-3b11-77a0-cc720afd6fe1@collabora.com> <9674d00e-c0d6-ceba-feab-5dc475bda694@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 8/11/22 01:03, Rob Clark wrote: > On Wed, Aug 10, 2022 at 12:26 PM Dmitry Osipenko > wrote: >> >> On 8/10/22 18:08, Rob Clark wrote: >>> On Wed, Aug 10, 2022 at 4:47 AM Daniel Vetter wrote: >>>> >>>> On Wed, Jul 06, 2022 at 10:02:07AM +0300, Dmitry Osipenko wrote: >>>>> On 7/6/22 00:48, Rob Clark wrote: >>>>>> On Tue, Jul 5, 2022 at 4:51 AM Christian König wrote: >>>>>>> >>>>>>> Am 01.07.22 um 11:02 schrieb Dmitry Osipenko: >>>>>>>> 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. 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. >>>>>>>> >>>>>>>> Majority of DRM drivers prohibit mapping of the imported GEM objects. >>>>>>>> Mapping of imported GEMs require special care from userspace since it >>>>>>>> should sync dma-buf because mapping coherency of the exporter device may >>>>>>>> not match the DRM device. Let's prohibit the mapping for all DRM drivers >>>>>>>> for consistency. >>>>>>>> >>>>>>>> Suggested-by: Thomas Hellström >>>>>>>> Signed-off-by: Dmitry Osipenko >>>>>>> >>>>>>> I'm pretty sure that this is the right approach, but it's certainly more >>>>>>> than possible that somebody abused this already. >>>>>> >>>>>> I suspect that this is abused if you run deqp cts on android.. ie. all >>>>>> winsys buffers are dma-buf imports from gralloc. And then when you >>>>>> hit readpix... >>>>>> >>>>>> You might only hit this in scenarios with separate gpu and display (or >>>>>> dGPU+iGPU) because self-imports are handled differently in >>>>>> drm_gem_prime_import_dev().. and maybe not in cases where you end up >>>>>> with a blit from tiled/compressed to linear.. maybe that narrows the >>>>>> scope enough to just fix it in userspace? >>>>> >>>>> Given that that only drivers which use DRM-SHMEM potentially could've >>>>> map imported dma-bufs (Panfrost, Lima) and they already don't allow to >>>>> do that, I think we're good. >>>> >>>> So can I have an ack from Rob here or are there still questions that this >>>> might go boom? >>>> >>>> Dmitry, since you have a bunch of patches merged now I think would also be >>>> good to get commit rights so you can drive this more yourself. I've asked >>>> Daniel Stone to help you out with getting that. >>> >>> I *think* we'd be ok with this on msm, mostly just by dumb luck. >>> Because the dma-buf's we import will be self-import. I'm less sure >>> about panfrost (src/panfrost/lib/pan_bo.c doesn't seem to have a >>> special path for imported dma-bufs either, and in that case they won't >>> be self-imports.. but I guess no one has tried to run android cts on >>> panfrost). >> >> The last time I tried to mmap dma-buf imported to Panfrost didn't work >> because Panfrost didn't implement something needed for that. I'll need >> to take a look again because can't recall what it was. >> >>> What about something less drastic to start, like (apologies for >>> hand-edited patch): >>> >>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c >>> index 86d670c71286..fc9ec42fa0ab 100644 >>> --- a/drivers/gpu/drm/drm_gem.c >>> +++ b/drivers/gpu/drm/drm_gem.c >>> @@ -1034,6 +1034,10 @@ int drm_gem_mmap_obj(struct drm_gem_object >>> *obj, unsigned long obj_size, >>> { >>> int ret; >>> >>> + WARN_ON_ONCE(obj->import_attach); >> >> This will hang NVIDIA Tegra, which is what this patch fixed initially. >> If neither of upstream DRM drivers need to map imported dma-bufs and >> never needed, then why do we need this? > > oh, tegra isn't using shmem helpers? I assumed it was. Well my point > was to make a more targeted fail on tegra, and a WARN_ON for everyone > else to make it clear that what they are doing is undefined behavior. > Because so far existing userspace (or well, panfrost and freedreno at > least, those are the two I know or checked) don't make special cases > for mmap'ing against the dmabuf fd against the dmabuf fd instead of > the drm device fd. It's not clear to me what bad Android does form yours comments. Does it export dma-buf from GPU and then import it to GPU? If yes, then DRM core has a check for the self-importing [1]. [1] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_prime.c#L918 If you're meaning something else, then please explain in a more details. > I *think* it should work out that we don't hit this path with > freedreno but on android I can't really guarantee or prove it. So > your patch would potentially break existing working userspace. Maybe > it is userspace that isn't portable (but OTOH it isn't like you are > going to be using freedreno on tegra). So why don't you go for a more > targeted fix that only returns an error on hw where this is > problematic? That's what the first versions of the patch did and Christian suggested that it's not a good approach. In fact it should be not only Tegra that has a broken dma-buf mapping, but apparently OMAP driver too. -- Best regards, Dmitry