linux-kernel - Re: memory allocation over 4gb under x86

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Message-Id: <20090304104424.dbc5692f.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 4 Mar 2009 10:44:24 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	protagora27 protagora27 <protagora27@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: memory allocation over 4gb under x86_64

On Tue, 3 Mar 2009 12:22:18 +0100
protagora27 protagora27 <protagora27@...il.com> wrote:

> Hello folks,
> 
> I have a 64 bit dma that I have to program with 64 bit physical
> address
> beyond 4 gb because I have to test dma with memory allocation beyond
> 4 gb.
> I 'm using linux x86_64 2.6.24 and I have 8 gb ram.
> How can I allocate physical dma memory beyond 4gb ? In x86_64
> can I use __pa to have physical address ?
> I have used kmalloc giving virtual address : ffff810225d10340
> and using __pa i have: 225d10340 that is over 8 gb .
> Does it mean that kmalloc return address is not linear mapped with phys ram ?
> 
IIUC, you can think that kmalloc() always retrun memory where __pa() works well.
Please check memory map of the host. It seems to have memory hole.

Thanks,
-Kame

> I would like to find a function that returns a physical adddres beyond
> 4gb
> and then i write phys address in dma register .
> 
> Thanks.
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