Date: Sun, 5 Apr 2015 09:54:53 +0800
From: Baoquan He <bhe@redhat.com>
To: Dave Young <dyoung@redhat.com>
Cc: "Li, ZhenHua" <zhen-hual@hp.com>, dwmw2@infradead.org,
        indou.takao@jp.fujitsu.com, joro@8bytes.org, vgoyal@redhat.com,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, kexec@lists.infradead.org,
        alex.williamson@redhat.com, ddutile@redhat.com,
        ishii.hironobu@jp.fujitsu.com, bhelgaas@google.com, doug.hatch@hp.com,
        jerry.hoemann@hp.com, tom.vaden@hp.com, li.zhang6@hp.com,
        lisa.mitchell@hp.com, billsumnerlinux@gmail.com, rwright@hp.com
Subject: Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel
Message-ID: <20150405015453.GB1562@dhcp-17-102.nay.redhat.com>
References: <1426743388-26908-1-git-send-email-zhen-hual@hp.com>
 <20150403084031.GF22579@dhcp-128-53.nay.redhat.com>
 <551E56F6.60503@hp.com>
 <20150403092111.GG22579@dhcp-128-53.nay.redhat.com>
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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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