linux-kernel - Re: Tough Issue: kernel instruction corruption

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Date:	Sat, 5 Jul 2008 23:26:57 +0800
From:	"Gavin Shan" <gshan@...atel-lucent.com>
To:	"Arjan van de Ven" <arjan@...radead.org>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: Tough Issue: kernel instruction corruption

>> Hello, I'm faced a tough issue recently: instructions of kernel
>> were corrupted. There has 2 PCI buses on my board and lots
>> of PCI devices with DMA capabality involved. I'm suspecting
>> the kernel instructions were corrupted by DMA operations driving
>> by those PCI devices with DMA capabality. 
>> 
>> Anybody have tried to protect kernel instructions from this case
>> or have any ideas to protect kernel text section?
> 
> if you have a modern Intel board, you can enable the IOMMU on it that
> will protect the kernel text (well, all of memory) from rogue DMA.
> PPC generally has similar capabilities, as do some IBM x86 chipsets.

PPC is used now and PPC doesn't have 2 kinds of MMUs. I don't know much
about IOMMU. Is it part of CPU?

> 
> Without an IOMMU it's basically impossible to protect against such DMA.

I did a google with "instruction"+"corruption"+"DMA" and found one matched
patent. And I go through the datasheet of PCI chips on my board, unfortunately,
the PCI chip didn't supply address protection from vager DMA.

http://www.freepatentsonline.com/y2005/0182862.html

> 
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