linux-kernel - Re: [PATCH] drm/fbdev-dma: fix getting smem

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Message-ID: <87cyomsiqt.fsf@minerva.mail-host-address-is-not-set>
Date: Wed, 12 Jun 2024 09:49:46 +0200
From: Javier Martinez Canillas <javierm@...hat.com>
To: Thomas Zimmermann <tzimmermann@...e.de>, "Peng Fan (OSS)"
 <peng.fan@....nxp.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Cc: Peng Fan <peng.fan@....com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/fbdev-dma: fix getting smem_start

Thomas Zimmermann <tzimmermann@...e.de> writes:

Hello Thomas,

> Hi
>
> Am 10.06.24 um 10:47 schrieb Thomas Zimmermann:
>> Hi
>>
>> Am 04.06.24 um 10:03 schrieb Peng Fan (OSS):
>>> From: Peng Fan <peng.fan@....com>
>>>
>>> If 'info->screen_buffer' locates in vmalloc address space, virt_to_page
>>> will not be able to get correct results. With CONFIG_DEBUG_VM and
>>> CONFIG_DEBUG_VIRTUAL enabled on ARM64, there is dump below:
>>
>> Which graphics driver triggers this bug?
>>
>>> [    3.536043] ------------[ cut here ]------------
>>> [    3.540716] virt_to_phys used for non-linear address: 
>>> 000000007fc4f540 (0xffff800086001000)
>>> [    3.552628] WARNING: CPU: 4 PID: 61 at arch/arm64/mm/physaddr.c:12 
>>> __virt_to_phys+0x68/0x98
>>> [    3.565455] Modules linked in:
>>> [    3.568525] CPU: 4 PID: 61 Comm: kworker/u12:5 Not tainted 
>>> 6.6.23-06226-g4986cc3e1b75-dirty #250
>>> [    3.577310] Hardware name: NXP i.MX95 19X19 board (DT)
>>> [    3.582452] Workqueue: events_unbound deferred_probe_work_func
>>> [    3.588291] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS 
>>> BTYPE=--)
>>> [    3.595233] pc : __virt_to_phys+0x68/0x98
>>> [    3.599246] lr : __virt_to_phys+0x68/0x98
>>> [    3.603276] sp : ffff800083603990
>>> [    3.677939] Call trace:
>>> [    3.680393]  __virt_to_phys+0x68/0x98
>>> [    3.684067]  drm_fbdev_dma_helper_fb_probe+0x138/0x238
>>> [    3.689214] __drm_fb_helper_initial_config_and_unlock+0x2b0/0x4c0
>>> [    3.695385]  drm_fb_helper_initial_config+0x4c/0x68
>>> [    3.700264]  drm_fbdev_dma_client_hotplug+0x8c/0xe0
>>> [    3.705161]  drm_client_register+0x60/0xb0
>>> [    3.709269]  drm_fbdev_dma_setup+0x94/0x148
>>>
>>> So add a check 'is_vmalloc_addr'.
>>>
>>> Fixes: b79fe9abd58b ("drm/fbdev-dma: Implement fbdev emulation for 
>>> GEM DMA helpers")
>>> Signed-off-by: Peng Fan <peng.fan@....com>
>>
>> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
>
> I'm taking back my r-b. The memory is expected to by be physically 
> contiguous and vmalloc() won't guarantee that.
>

Agreed.

> Best regards
> Thomas
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat