linux-kernel - Re: [PATCH] x86: Fix CPA memtype reserving in the set_pages

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Date:	Mon, 3 Aug 2009 11:19:54 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Hellstrom <thellstrom@...are.com>
Cc:	Dave Airlie <airlied@...ux.ie>,
	Arjan van de Ven <arjan@...radead.org>,
	"suresh.b.siddha@...el.com" <suresh.b.siddha@...el.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"venkatesh.pallipadi@...el.com" <venkatesh.pallipadi@...el.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"dri-devel@...ts.sourceforge.net" <dri-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] x86: Fix CPA memtype reserving in the set_pages_array
	cases


* Thomas Hellstrom <thellstrom@...are.com> wrote:

> Dave Airlie wrote:
>>> hm, i'm missing a description about how this bug was triggered. How 
>>> did you end up getting highmem pages to a cpa call?
>>>     
>>
>> GEM and TTM both allocate page arrays and just pass them to cpa,
>> we don't know what type of pages the allocator gives us back and we 
>> really shouldn't have to, so having cpa ignore highmem pages is 
>> certainly the right option.
>>
>> GEM just uses shmem code to alloc the pages and TTM has its own allocator.
>>
>>   
> Yes, Dave is right.
>
> Although I'm not 100% sure the TTM code I was using that triggered this  
> has made it into 2.6.31.
> Old AGP uses (GFP_KERNEL | GFP_DMA32 | __GFP_ZERO), which (correct me if  
> I'm wrong) never hands back highmem pages. This means that Intel's GEM  
> is the only likely user for 2.6.31.

(please dont top-post) I'm not sure you folks noticed this bit of my 
mail:

>>> ok, that's a bug introduced in .29 but which was latent until now:  
>>> drivers/char/agp/generic.c now uses it plus (indirectly) a number of  
>>> AGP drivers, since:
>>>
>>>  commit 07613ba2f464f59949266f4337b75b91eb610795
>>>  Author: Dave Airlie <airlied@...hat.com>
>>>  Date:   Fri Jun 12 14:11:41 2009 +1000
>>>
>>>      agp: switch AGP to use page array instead of unsigned long array
>>>
>>> I dont see how it can end up with highmem pages though. All the 
>>> graphics apperture allocations happen to lowmem AFAICS. Did GEM add 
>>> the possibility for user pages (highmem amongst them) ending up in 
>>> that pool? Which code does that?

	Ingo
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