linux-kernel - Re: [PATCH v11 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

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Message-ID: <20150610092150.GZ20384@8bytes.org>
Date:	Wed, 10 Jun 2015 11:21:51 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	bhe@...hat.com, tom.vaden@...com, rwright@...com,
	linux-pci@...r.kernel.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, lisa.mitchell@...com,
	iommu@...ts.linux-foundation.org,
	"Li, Zhen-Hua" <zhen-hual@...com>, doug.hatch@...com,
	ishii.hironobu@...fujitsu.com, bhelgaas@...gle.com,
	billsumnerlinux@...il.com, li.zhang6@...com, dyoung@...hat.com,
	vgoyal@...hat.com
Subject: Re: [PATCH v11 0/10] iommu/vt-d: Fix intel vt-d faults in kdump
 kernel

On Tue, Jun 09, 2015 at 01:55:50PM +0100, David Woodhouse wrote:
> On Mon, 2015-06-08 at 18:13 +0200, Joerg Roedel wrote:
> > So I think we need to read out that bit when we find translation enabled
> > and if it is different from what we would set it to, we bail out of any
> > copying, disable translation and proceed as in a normal boot.
> 
> Given that this is only for kdump and not the general case of kexec,
> that's probably tolerable. Of course we do still need to make it *not*
> broken for the case where DMA_RTADDR_RTT is set, as it is at the
> moment.

Yes, I just sent a patch for this and will include it into my x86/vt-d
branch if not objections come in.

> And I suspect if we're doing that, it might be simple enough to make it
> convert to/from the extended page tables. I don't think we want to
> preserve PASID tables; only the "second level" (i.e. traditional)
> translation. So we could happily pull the page table pointer out of
> either kind of context entry, and install it into either kind. I think
> there's a simple mapping of translation types too. I need to sort out
> the translation types when adding the real PASID support (imminently!)
> anyway.

What happens when we take away the PASID tables from a device? Can it
also go into some failure state?
When doing this, we need at least setup the page request queue before we
copy over anything and change the root-entry. Then we can handle any
faults that are caused by this and tell the device to not try further.


	Joerg

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