linux-kernel - Re: [PATCH] x86-64: disable the GART before allocate aperture

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Message-Id: <200706230214.02535.ak@suse.de>
Date:	Sat, 23 Jun 2007 02:14:01 +0200
From:	Andi Kleen <ak@...e.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Muli Ben-Yehuda <muli@...ibm.com>,
	Yinghai Lu <Yinghai.Lu@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86-64: disable the GART before allocate aperture

On Saturday 23 June 2007 00:19:51 Alan Cox wrote:
> > YH do you think you can look at simply reserving a portion of the iommu?
> > And having the kexec on panic kernel use the reserved portion?
> 
> How about simply reserving all of it for the base kernel and using soft
> iommu for the panic kernel, its hardly high performance criticial at this
> point.

The kdump kernel should be normally all <4GB anyways. You won't
need any IOMMU for its IO unless you O_DIRECT/sendfile out of /proc/kcore.
Just don't do that (but I suspect it won't work anyways)

If it's not then swiotlb will also not work because it won't get 
any memory <4GB.

But I doubt this was YH's problem - the panic kernel memory
is always reserved and there shouldn't be any ongoing DMAs in this
area anyways. And what happens outside the kdump kernel shouldn't matter.

I suspect he rather saw problems with non kdump kexec where we
can just shut down the GART properly beforehand.

-Andi
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