linux-kernel - Re: [PATCH v10 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

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Message-ID: <20150424083530.GD4458@dhcp-16-116.nay.redhat.com>
Date:	Fri, 24 Apr 2015 16:35:30 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Dave Young <dyoung@...hat.com>
Cc:	"Li, ZhenHua" <zhen-hual@...com>, dwmw2@...radead.org,
	indou.takao@...fujitsu.com, joro@...tes.org, 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 v10 0/10] iommu/vt-d: Fix intel vt-d faults in kdump
 kernel

On 04/24/15 at 04:25pm, Dave Young wrote:
> Hi, Baoquan
> 
> > I support this patchset.
> > 
> > We should not fear oldmem since reserved crashkernel region is similar.
> > No one can guarantee that any crazy code won't step into crashkernel
> > region just because 1st kernel says it's reversed for kdump kernel. Here
> > the root table and context tables are also not built to allow legal code
> > to danamge. Both of them has the risk to be corrupted, for trying our
> > best to get a dumped vmcore the risk is worth being taken.
> 
> old mem is mapped in 1st kernel so compare with the reserved crashkernel
> they are more likely to be corrupted. they are totally different. 

Could you tell how and why they are different? Wrong code will choose
root tables and context tables to danamge when they totally lose
control?

> 
> > 
> > And the resetting pci way has been NACKed by David Woodhouse, the
> > maintainer of intel iommu. Because the place calling the resetting pci
> > code is ugly before kdump kernel or in kdump kernel. And as he said a
> > certain device made mistakes why we blame on all devices. We should fix
> > that device who made mistakes. 
> 
> Resetting pci bus is not ugly than fixing a problem with risk and to fix
> the problem it introduced in the future.

There's a problem, we fix the problem. If that's uglier, I need redefine
the 'ugly' in my personal dict. You mean the problem it could introduce
is wrong code will damage root table and context tables, why don't we
fix that wrong code, but blame innocent context tables? So you mean
these tables should deserve being damaged by wrong code?

> 
> I know it is late to speak out, but sorry I still object and have to NACK this
> oldmem approach from my point.
> 
> Thanks
> Dave
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