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

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Message-ID: <e307fdc0-553d-4946-9017-ed3a28e9cae2@suse.de>
Date: Wed, 12 Jun 2024 08:48:32 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: "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>,
 Javier Martinez Canillas <javierm@...hat.com>
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

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.

Best regards
Thomas

>
> Best regards
> Thomas
>
>> ---
>>   drivers/gpu/drm/drm_fbdev_dma.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_fbdev_dma.c 
>> b/drivers/gpu/drm/drm_fbdev_dma.c
>> index 6c9427bb4053..9e2eddb6eb5c 100644
>> --- a/drivers/gpu/drm/drm_fbdev_dma.c
>> +++ b/drivers/gpu/drm/drm_fbdev_dma.c
>> @@ -130,7 +130,12 @@ static int drm_fbdev_dma_helper_fb_probe(struct 
>> drm_fb_helper *fb_helper,
>>           info->flags |= FBINFO_READS_FAST; /* signal caching */
>>       info->screen_size = sizes->surface_height * fb->pitches[0];
>>       info->screen_buffer = map.vaddr;
>> -    info->fix.smem_start = 
>> page_to_phys(virt_to_page(info->screen_buffer));
>> +
>> +    if (is_vmalloc_addr(info->screen_buffer))
>> +        info->fix.smem_start = 
>> page_to_phys(vmalloc_to_page(info->screen_buffer));
>> +    else
>> +        info->fix.smem_start = 
>> page_to_phys(virt_to_page(info->screen_buffer));
>> +
>>       info->fix.smem_len = info->screen_size;
>>         return 0;
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)