linux-kernel - Re: [PATCH 3/4] Revert "x86: disable IOMMUs on kernel crash"

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Date:	Sun, 04 Apr 2010 00:51:10 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Bernhard Walle <bernhard@...lle.de>
Cc:	Joerg Roedel <joro@...tes.org>, nhorman@...hat.com,
	nhorman@...driver.com, Joerg Roedel <joerg.roedel@....com>,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Chris Wright <chrisw@...s-sol.org>, hbabu@...ibm.com,
	iommu@...ts.linux-foundation.org, vgoyal@...hat.com
Subject: Re: [PATCH 3/4] Revert "x86: disable IOMMUs on kernel crash"

Bernhard Walle <bernhard@...lle.de> writes:

> Am 03.04.10 19:49, schrieb Eric W. Biederman:
>> Not a problem.  We require a lot of things of the kdump kernel,
>> and it is immediately apparent in a basic sanity test.
>
> Also, in most cases (for example: distribution kernels), the kdump
> kernel nowadays is identical to the running kernel. So, if the running
> kernel has IOMMU support, the kdump kernel also has.

I have been rather pleasantly surprised at how well that works.  Although
I am still glad I insisted that using the same kernel version not be a
hard requirement.  It allowed us to specify a good solid interface.

How to cope with GART in that situation without having to manually specify
iommu=off in the configuration I find a more compelling question.

I expect I will have a look at that in the coming months if someone doesn't get
there before I do.

Eric
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