Message-ID: <45364D9D.2060003@biallas.net>
Date: Wed, 18 Oct 2006 17:51:57 +0200
From: Sebastian Biallas <sb@biallas.net>
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To: Prakash Punnoor <prakash@punnoor.de>
CC: linux-kernel@vger.kernel.org
Subject: Re: PCI-DMA: Disabling IOMMU
References: <45364248.2020901@biallas.net> <200610181741.03428.prakash@punnoor.de>
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Prakash Punnoor wrote:
> Am Mittwoch 18 Oktober 2006 17:03 schrieben Sie:
>> Linux ouputs some strange "PCI-DMA: Disabling IOMMU" on booting. It's a
>> ALiveNF4G motherboard with an Athlon64 X2 running vanilla Linux 2.6.18.1
>> (which supports all hardware out of the box, pretty cool).
>>
>> Should I worry about this IOMMU-disabling? All other Linux/IOMMU stuff I
>> found had AGP or BIOS messages nearby, but I only get this single
>> "PCI-DMA: Disabling IOMMU" line, without any hint.
> 
> Unless you have >=4GB of RAM using IOMMU makes no sense, thus it gets 
> disabled.

Thanks for the answer (I thought that IOMMU is also used by VMMs like
XEN, for direct hardware access of the guest. But I might have
misunderstood this).

So maybe this message should read:
PCI-DMA: Not more than 4GiB RAM: Disabling IOMMU
so that people like me don't have to worry.

Regards,
Sebastian

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