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Reply-To: <imran.badr@cavium.com>
From: "Imran Badr" <imran.badr@cavium.com>
To: "'Andrew Morton'" <akpm@digeo.com>,
       "'Daniel Phillips'" <phillips@arcor.de>
Cc: <root@chaos.analogic.com>, "'David S. Miller'" <davem@redhat.com>,
       <linux-kernel@vger.kernel.org>
Subject: RE: Calculating kernel logical address ..
Date: Mon, 9 Sep 2002 12:23:20 -0700
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-----Original Message-----
From: linux-kernel-owner@vger.kernel.org
[mailto:linux-kernel-owner@vger.kernel.org]On Behalf Of Andrew Morton
Sent: Monday, September 09, 2002 12:15 PM
To: Daniel Phillips
Cc: imran.badr@cavium.com; root@chaos.analogic.com; 'David S. Miller';
linux-kernel@vger.kernel.org
Subject: Re: Calculating kernel logical address ..


Daniel Phillips wrote:
>
> ...
> > down(&current->mm->mmap_sem) would help.
>
> Not for anon pages, and how do you know whether it's anon or not before
> looking at the page, which may be free by the time you look at it?
> In other words, mm->page_table_lock is the one, because it's required
> for unmapping a pte, and any mapped page will be forced to hold a count
> increment until it gets past that lock.  Without this lock, the results
> of pte_page are unstable.

>The caller of get_user_pages() needs to hold mmap_sem for reading
>to prevent the vmas from going away.  get_user_pages() does the
>right thing wrt page_table_lock.  (As a quick peek at the code
>would reveal...)
>-
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So, I am hearing the get_user_pages is the right choice for me. BTW, did
anybody take a look at the code snippet that posted earlier? That code
mmap's kmalloc'ed memory to process space and then in the ioctl call, I
calculate kernel logical address.
Please have a look and advise any portability issue.

Thanks,
Imran.


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