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

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Message-ID: <20150415064803.GF19051@localhost.localdomain>
Date:	Wed, 15 Apr 2015 14:48:03 +0800
From:	Dave Young <dyoung@...hat.com>
To:	"Li, ZhenHua" <zhen-hual@...com>
Cc:	dwmw2@...radead.org, indou.takao@...fujitsu.com, bhe@...hat.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 04/15/15 at 01:47pm, Li, ZhenHua wrote:
> On 04/15/2015 08:57 AM, Dave Young wrote:
> >Again, I think it is bad to use old page table, below issues need consider:
> >1) make sure old page table are reliable across crash
> >2) do not allow writing oldmem after crash
> >
> >Please correct me if I'm wrong, or if above is not doable I think I will vote for
> >resetting pci bus.
> >
> >Thanks
> >Dave
> >
> Hi Dave,
> 
> When updating the context tables, we have to write their address to root
> tables, this will cause writing to old mem.
> 
> Resetting the pci bus has been discussed, please check this:
> http://lists.infradead.org/pipermail/kexec/2014-October/012752.html
> https://lkml.org/lkml/2014/10/21/890

I know one reason to use old pgtable is this looks better because it fixes the
real problem, but it is not a good way if it introduce more problems because of
it have to use oldmem. I will be glad if this is not a problem but I have not
been convinced.

OTOH, there's many types of iommu, intel, amd, a lot of other types. They need
their own fixes, so it looks not that elegant.

For pci reset, it is not perfect, but it has another advantage, the patch is
simpler. The problem I see from the old discusssion is, reset bus in 2nd kernel
is acceptable but it does not fix things on sparc platform. AFAIK current reported
problems are intel and amd iommu, at least pci reset stuff does not make it worse.

Thanks
Dave
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