linux-kernel - Re: [PATCH 00/19] Fix Intel IOMMU breakage in kdump kernel

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Message-ID: <1435066290.12045.2.camel@infradead.org>
Date:	Tue, 23 Jun 2015 14:31:30 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Joerg Roedel <joro@...tes.org>, iommu@...ts.linux-foundation.org
Cc:	zhen-hual@...com, bhe@...hat.com, ddutile@...hat.com,
	alex.williamson@...hat.com, dyoung@...hat.com,
	linux-kernel@...r.kernel.org, jroedel@...tes.org
Subject: Re: [PATCH 00/19] Fix Intel IOMMU breakage in kdump kernel

On Sat, 2015-06-13 at 08:47 +0200, Joerg Roedel wrote:
> Hi,
> 
> as David Woodhouse pointed out, my fixes and cleanups for
> the original patch-set turned out to be a complete rewrite.
> So to have a cleaner history of the feature and to make
> backporting easier, here is a rewrite of my changes based on
> v4.1-rc7.
> 
> Some additional issues have been fixed by this rewrite, like
> a kdump-kernel boot panic with 'iommu=pt' and support for
> copying the extended root-entry and context table formats
> has been added.

This looks much better than before; thanks.

However, it's still fairly gratuitous for all non-broken hardware, and
will tend to hide hardware and driver bugs during testing of new
hardware.

I'd much rather see this limited to a blacklist of known-broken
devices, an accompanied by a kernel message along the lines of

 'Preserving VT-d page tables for broken HP device xxxx:xxxx'

For *any* device which isn't so broken that it craps itself on taking a
DMA fault and cannot be reset, this page table copy shouldn't be
needed, right?


-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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