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

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Message-ID: <20081113034425.GA23434@wotan.suse.de>
Date:	Thu, 13 Nov 2008 04:44:25 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
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

On Wed, Nov 12, 2008 at 04:02:47PM -0800, Pallipadi, Venkatesh wrote:
>  
> 
> >-----Original Message-----
> >From: Nick Piggin [mailto:npiggin@...e.de] 
> >Sent: Wednesday, November 12, 2008 3:23 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
> >
> >You have to be careful of this, because it can be called with mmap_sem
> >held for read only. Hmm, I guess vm_insert_page is doing the 
> >same thing.
> >Probably mostly works because all other modifiers of vm_flags 
> >are holding
> >mmap_sem.
> 
> Yes. I did the patch looking at vm_insert_page doing similar thing.
> 
> >
> >However, in some cases, code can do vm_insert_pfn and vm_insert_page
> >(actually hmm, no vm_insert_mixed actually should cover most of those
> >cases).
> >
> >Still, I'd be much happier if we could make these into BUG_ON, and then
> >teach callers to set it in their .mmap routines.
> 
> Actually, vm_insert_pfn() already has a BUG_ON() at the start for cases
> where neither (or both) MIXEDMAP and PFNMAP is not set. So, that should
> cover the case we are worried about it here and we can eliminate this
> patch altogether. Only part I am not sure about is why we are looking
> for MIXEDMAP here. Shouldn't they be using vm_insert_mixed instead?

They should, but it will do an inesrt_pfn in some cases, won't it?
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