linux-kernel - RE: [patch 2/8] x86 PAT: set VM_PFNMAP flag in vm_insert

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Date:	Fri, 14 Nov 2008 13:35:38 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Nick Piggin <npiggin@...e.de>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Hugh Dickins <hugh@...itas.com>,
	Roland Dreier <rdreier@...co.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Arjan van de Ven <arjan@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Subject: RE: [patch 2/8] x86 PAT: set VM_PFNMAP flag in vm_insert_pfn



>-----Original Message-----
>From: Nick Piggin [mailto:npiggin@...e.de]
>Sent: Thursday, November 13, 2008 6:06 PM
>To: Pallipadi, Venkatesh
>Cc: Ingo Molnar; Thomas Gleixner; H Peter Anvin; Hugh Dickins;
>Roland Dreier; Jesse Barnes; Jeremy Fitzhardinge; Arjan van de
>Ven; linux-kernel@...r.kernel.org; Siddha, Suresh B
>Subject: Re: [patch 2/8] x86 PAT: set VM_PFNMAP flag in vm_insert_pfn
>
>On Thu, Nov 13, 2008 at 10:47:23AM -0800, Pallipadi, Venkatesh wrote:
>>
>> Yes. It does. But, it calls a lower level insert_pfn()
>function. The lower
>> level insert_pfn() does not have any bug checks. But the higher level
>> vm_insert_pfn() checks for PFNMAP or MIXEDMAP.
>
>Yes, but is there anything extra you need to check for cache aliases in
>MIXEDMAP mappings?
>

Yes. We need additional things to track MIXEDMAP and we are looking at that.
But, that is slightly more trickier than the general PFNMAP case. And
only in-tree user of MIXEDMAP is xip and that too it only uses it for
regular WB mapping. So, we thought we should fix the more common case
first here.

With MIXEDMAP there is no way whether to distinguish whether insert_pfn
Or insert_page was used while looking at VMA. We can probably use PFNMAP
in addition to MIXEDMAP to indicate that, which will make things easier.
But, we are still looking at that and trying to understand the change
implication.

Thanks,
Venki
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