linux-kernel - Re: [PATCH retry] intel-iommu:make identity

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Date:	Tue, 01 Nov 2011 17:52:28 +0800
From:	Dave Young <dyoung@...hat.com>
To:	David Woodhouse <dwmw2@...radead.org>
CC:	kexec@...ts.infradead.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, vgoyal@...hat.com,
	horms@...ge.net.au, luyu@...hat.com
Subject: Re: [PATCH retry] intel-iommu:make identity_map default for crash
 dump

On 11/01/2011 05:34 PM, David Woodhouse wrote:

> On Tue, 2011-11-01 at 17:19 +0800, Dave Young wrote:
>> kdump kernel sometimes will get DMAR faults which
>> is caused by random in-flight dma from 1st kernel
>>
>> Here make the identity_mapping as default for this case
> 
> So you want to *allow* the random in-flight DMA? And with an identity
> mapping it's really going to random addresses, since it'll be
> untranslated and won't even go to the physical addresses which it was
> originally intended for?
> 
> This seems entirely broken to me.
> 
> If there is "random in-flight dma" from the first kernel, the correct
> thing to do is *block* it. Which is what we do.
> 


This patch works for me for several cases. For kdump It can be seen a
workaround. But yes blocking the 1st kernel dma is ideal.

Glad to hear that you are working on this.

-- 
Thanks
Dave
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