linux-kernel - Re: [PATCH] drm: make sure page protections are updated after changing vm

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Message-ID: <4ACBB725.4010605@goop.org>
Date:	Tue, 06 Oct 2009 14:31:17 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	airlied@...ux.ie, dri-devel@...ts.sourceforge.net,
	JBeulich@...ell.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: make sure page protections are updated after changing
 vm_flags.

On 10/06/09 13:39, Andrew Morton wrote:
> On Wed, 30 Sep 2009 15:55:39 -0700
> Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>
>   
>> Some architectures compute ->vm_page_prot depending on ->vm_flags, so
>> we need to update the protections after adjusting the flags.
>>
>> Reported-by: Jan Beulich <JBeulich@...ell.com>
>> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
>>
>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>> index 8104eca..9d3e39f 100644
>> --- a/drivers/gpu/drm/drm_gem.c
>> +++ b/drivers/gpu/drm/drm_gem.c
>> @@ -537,7 +537,7 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
>>  	vma->vm_ops = obj->dev->driver->gem_vm_ops;
>>  	vma->vm_private_data = map->handle;
>>  	/* FIXME: use pgprot_writecombine when available */
>> -	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
>> +	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
>>  
>>  	/* Take a ref for this mapping of the object, so that the fault
>>  	 * handler can dereference the mmap offset's pointer to the object.
>>     
> u fail changelogology.
>
> What were the consequences of the bug which you just fixed?
>   

AFAIK this only affects running X under Xen; without this patch you get
lots of coloured blobs on the screen, or maybe a complete lockup.  Or
anything really.

But that still depends on lots of out-of-tree stuff, so I don't think
there are any consequences for anyone else.  But it is wrong in principle.

    J
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