linux-kernel - Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

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Date:	Tue, 5 May 2015 14:09:31 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	"Li, Zhen-Hua" <zhen-hual@...com>, dwmw2@...radead.org,
	indou.takao@...fujitsu.com, bhe@...hat.com, vgoyal@...hat.com,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, kexec@...ts.infradead.org,
	alex.williamson@...hat.com, ddutile@...hat.com,
	ishii.hironobu@...fujitsu.com, bhelgaas@...gle.com,
	doug.hatch@...com, jerry.hoemann@...com, tom.vaden@...com,
	li.zhang6@...com, lisa.mitchell@...com, billsumnerlinux@...il.com,
	rwright@...com
Subject: Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

On 05/04/15 at 01:05pm, Joerg Roedel wrote:
> On Fri, Apr 03, 2015 at 04:40:31PM +0800, Dave Young wrote:
> > Have not read all the patches, but I have a question, not sure this
> > has been answered before. Old memory is not reliable, what if the old
> > memory get corrupted before panic? Is it safe to continue using it in
> > 2nd kernel, I worry that it will cause problems.
> 
> Yes, the old memory could be corrupted, and there are more failure cases
> left which we have no way of handling yet (if iommu data structures are
> in kdump backup areas).
> 
> The question is what to do if we find some of the old data structures
> corrupted, hand how far should the tests go. Should we also check the
> page-tables, for example? I think if some of the data structures for a
> device are corrupted it probably already failed in the old kernel and
> things won't get worse in the new one.

I agree that we can do nothing with the old corrupted data, but I worry
about the future corruption after using the old corrupted data. I wonder
if we can mark all the oldmem as readonly so that we can lower the risk.
Is it resonable?

Thanks
Dave
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