linux-kernel - Re: [PATCH] drm/ttm: provide default page protection for UML

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Message-ID: <0887903c-483d-49c7-0d35-f59be2f85bac@cambridgegreys.com>
Date:   Thu, 2 Sep 2021 07:19:01 +0100
From:   Anton Ivanov <anton.ivanov@...bridgegreys.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Cc:     Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Christian König <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>, dri-devel@...ts.freedesktop.org,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        linux-um@...ts.infradead.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm/ttm: provide default page protection for UML

On 02/09/2021 06:52, Randy Dunlap wrote:
> On 9/1/21 10:48 PM, Anton Ivanov wrote:
>> On 02/09/2021 03:01, Randy Dunlap wrote:
>>> boot_cpu_data [struct cpuinfo_um (on UML)] does not have a struct
>>> member named 'x86', so provide a default page protection mode
>>> for CONFIG_UML.
>>>
>>> Mends this build error:
>>> ../drivers/gpu/drm/ttm/ttm_module.c: In function 
>>> ‘ttm_prot_from_caching’:
>>> ../drivers/gpu/drm/ttm/ttm_module.c:59:24: error: ‘struct cpuinfo_um’ 
>>> has no member named ‘x86’
>>>    else if (boot_cpu_data.x86 > 3)
>>>                          ^
>>>
>>> Fixes: 3bf3710e3718 ("drm/ttm: Add a generic TTM memcpy move for 
>>> page-based iomem")
>>> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
>>> Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
>>> Cc: Christian König <christian.koenig@....com>
>>> Cc: Huang Rui <ray.huang@....com>
>>> Cc: dri-devel@...ts.freedesktop.org
>>> Cc: Jeff Dike <jdike@...toit.com>
>>> Cc: Richard Weinberger <richard@....at>
>>> Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
>>> Cc: linux-um@...ts.infradead.org
>>> Cc: David Airlie <airlied@...ux.ie>
>>> Cc: Daniel Vetter <daniel@...ll.ch>
>>> ---
>>>   drivers/gpu/drm/ttm/ttm_module.c |    4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> --- linux-next-20210901.orig/drivers/gpu/drm/ttm/ttm_module.c
>>> +++ linux-next-20210901/drivers/gpu/drm/ttm/ttm_module.c
>>> @@ -53,6 +53,9 @@ pgprot_t ttm_prot_from_caching(enum ttm_
>>>       if (caching == ttm_cached)
>>>           return tmp;
>>> +#ifdef CONFIG_UML
>>> +    tmp = pgprot_noncached(tmp);
>>> +#else
>>>   #if defined(__i386__) || defined(__x86_64__)
>>>       if (caching == ttm_write_combined)
>>>           tmp = pgprot_writecombine(tmp);
>>> @@ -69,6 +72,7 @@ pgprot_t ttm_prot_from_caching(enum ttm_
>>>   #if defined(__sparc__)
>>>       tmp = pgprot_noncached(tmp);
>>>   #endif
>>> +#endif
>>>       return tmp;
>>>   }
>>
>> Patch looks OK.
>>
>> I have a question though - why all of DRM is not !UML in config. Not 
>> like we can use them.
> 
> I have no idea about that.
> Hopefully one of the (other) UML maintainers can answer you.

Touche.

We will discuss that and possibly push a patch to !UML that part of the 
tree. IMHO it is not applicable.

A.

> 
> thanks.


-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/