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

[Baoquan He]

On 04/03/15 at 05:21pm, Dave Young wrote:
> On 04/03/15 at 05:01pm, Li, ZhenHua wrote:
> > Hi Dave,
> > 
> > There may be some possibilities that the old iommu data is corrupted by
> > some other modules. Currently we do not have a better solution for the
> > dmar faults.
> > 
> > But I think when this happens, we need to fix the module that corrupted
> > the old iommu data. I once met a similar problem in normal kernel, the
> > queue used by the qi_* functions was written again by another module.
> > The fix was in that module, not in iommu module.
> 
> It is too late, there will be no chance to save vmcore then.
> 
> Also if it is possible to continue corrupt other area of oldmem because
> of using old iommu tables then it will cause more problems.
> 
> So I think the tables at least need some verifycation before being used.
> 

Yes, it's a good thinking anout this and verification is also an
interesting idea. kexec/kdump do a sha256 calculation on loaded kernel
and then verify this again when panic happens in purgatory. This checks
whether any code stomps into region reserved for kexec/kernel and corrupt
the loaded kernel.

If this is decided to do it should be an enhancement to current
patchset but not a approach change. Since this patchset is going very
close to point as maintainers expected maybe this can be merged firstly,
then think about enhancement. After all without this patchset vt-d often
raised error message, hung.

By the way I tested this patchset it works very well on my HP z420 work
station.

Thanks
Baoquan
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