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 for kexec@lists.infradead.org; Wed, 27 Dec 2017 12:44:49 +0000
Date: Wed, 27 Dec 2017 20:44:29 +0800
From: Baoquan He <bhe@redhat.com>
Subject: Re: [PATCH v2] x86/kexec: Exclude GART aperture from vmcore
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To: Borislav Petkov <bp@alien8.de>
Cc: Jiri Bohac <jbohac@suse.cz>, Toshi Kani <toshi.kani@hpe.com>, David Airlie <airlied@linux.ie>, yinghai@kernel.org, joro@8bytes.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Bjorn Helgaas <bhelgaas@google.com>, Thomas Gleixner <tglx@linutronix.de>, Dave Young <dyoung@redhat.com>, Vivek Goyal <vgoyal@redhat.com>

On 12/27/17 at 01:25pm, Borislav Petkov wrote:
> On Wed, Dec 27, 2017 at 03:44:49PM +0800, Baoquan He wrote:
> > > yes, instead of crashing the machine (because GART may be initialized in the
> > > 2nd kernel, overlapping the 1st kernel memory, which the 2nd kernel with its
> > > fake e820 map sees as unused).
> > > 
> > > I'd say this is an improvement.
> > 
> > I don't get what you said. If 'iommu=off' only specified in 1st kernel,
> > kdump kernel will think the memory which GART bar pointed as a hole.
> > This is incorrect. I don't see the improvement.
> 
> So he says, this memory is unused. Why is that incorrect?!?

'iommu=off' specified in 1st kernel, that region will be normal memory,
there could be important kernel data written into the place. While kdump
kernel will take that region as a gart aperture, trying to read data
from that region will cause error which Jiri originally tried to fix.


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