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

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Message-ID: <20150504110551.GD15736@8bytes.org>
Date:	Mon, 4 May 2015 13:05:51 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Dave Young <dyoung@...hat.com>
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 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.

So checking is not strictly necessary in the first version of these
patches (unless we find a valid failure scenario). Once we have some
good plan on what to do if we find corruption, we can add checking of
course.

Regards,

	Joerg

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