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

[Andi Kleen <ak@suse.de>]

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