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

From: Li, ZhenHua
Date: Mon Apr 20 2015 - 21:40:39 EST


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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