linux-kernel - Re: [PATCH v7 2/2] drm/gem: Don't map imported GEMs

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Date:   Thu, 30 Jun 2022 23:22:59 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>, David Airlie <airlied@...ux.ie>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Christian König <christian.koenig@....com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>,
        linux-tegra@...r.kernel.org, kernel@...labora.com,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v7 2/2] drm/gem: Don't map imported GEMs

Hello Thomas,

On 6/30/22 23:15, Thomas Hellström (Intel) wrote:
> Hi, Dmitry,
> 
> On 6/30/22 22:04, 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. 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.
>>
>> Cc: stable@...r.kernel.org
>> Suggested-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> 
> This might break drivers whose obj->funcs->mmap() callback already
> handles this case, and has userspace that does the right thing.

The drm-shmem helper should be the only that maps imported GEMs
properly, but drivers that use drm-shmem already prohibit to map
imported GEMs. Okay, I'll try to re-check once again to be sure.

> I think the disabling must be checked on a per-driver basis to avoid
> that; in particular drivers that already call dma_buf_mmap() should be
> able to continue doing this.
> 
> Also the Fixes: review comment remains,

This should've been broken forever, don't think that we have a fixes tag
here. I looked thought all my previous patches and added the Fixes
wherever was possible. If I really missed something, then please let me
know.

-- 
Best regards,
Dmitry