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

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Message-ID: <5535AA57.6010404@hp.com>
Date:	Tue, 21 Apr 2015 09:39:35 +0800
From:	"Li, ZhenHua" <zhen-hual@...com>
To:	Dave Young <dyoung@...hat.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, "Li, ZhenHua" <zhen-hual@...com>
Subject: Re: [PATCH v10 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

Hi Dave,
I found the old mail:
http://lkml.iu.edu/hypermail/linux/kernel/1410.2/03584.html

Please check this and you will find the discussion.

Regards
Zhenhua

On 04/15/2015 02:48 PM, Dave Young wrote:
> 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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