Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <22005f1b-4ae2-0fda-beda-1d9847bb2ade@shipmail.org>
Date:   Thu, 30 Jun 2022 22:26:37 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.0
Subject: Re: [PATCH v7 2/2] drm/gem: Don't map imported GEMs
Content-Language: en-US
To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>,
        David Airlie <airlied@linux.ie>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Emil Velikov <emil.l.velikov@gmail.com>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Dmitry Osipenko <digetx@gmail.com>,
        linux-tegra@vger.kernel.org, kernel@collabora.com,
        virtualization@lists.linux-foundation.org
References: <20220630200405.1883897-1-dmitry.osipenko@collabora.com>
 <20220630200405.1883897-3-dmitry.osipenko@collabora.com>
 <75b677b6-c704-e270-c921-93c982020c38@shipmail.org>
 <8ab15669-889b-1119-9323-ec47689c7fb7@collabora.com>
From:   =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28Intel=29?= 
        <thomas_os@shipmail.org>
In-Reply-To: <8ab15669-889b-1119-9323-ec47689c7fb7@collabora.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 6/30/22 22:22, Dmitry Osipenko wrote:
> 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@vger.kernel.org
>>> Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.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.

OK. If you aren't 100.1% sure, then please drop the Cc: stable tag and 
let the patch ride out at least an -rc series, because breaking a stable 
kernel is something we woudln't want to do.

Thanks,

Thomas


>
>> 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.
>