Date: Mon, 11 Mar 2013 16:17:25 -0400
From: Vivek Goyal <vgoyal@redhat.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Yinghai Lu <yinghai@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, WANG Chao <chaowang@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86, kdump: Set crashkernel_low automatically
Message-ID: <20130311201725.GD14738@redhat.com>
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On Mon, Mar 11, 2013 at 12:59:44PM -0700, H. Peter Anvin wrote:
> On 03/11/2013 12:22 PM, Vivek Goyal wrote:
> > 
> > So always reserving memory at highest address will break all the cases
> > which work without iommu and rely on swiotlb. I think first we need
> > to make sure that kdump works reliably with iommu on, and then try
> > to move to always reserving memory at higest possible address.
> > 
> 
> We should clearly always reserve an swiotlb window, *or*, probably much
> better, teach the kdump kernel to *make* an swiotlb window (by having a
> memory buffer in its reserved memory area into which it copies a chunk
> of low memory, just as we do for the bottom megabyte.  If we are already
> in low memory that buffer becomes the swiotlb window, no copy necessary.)

This sounds like a good idea. It will require exporting how much memory
should be needed for swiotlb. And then kexec-tools should be able to 
backup that memory area and make that memory available to second kernel.

Thanks
Vivek
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