linux-kernel - Re: [PATCH v2] intel-iommu: Quiesce devices before disabling IOMMU

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Date:	Tue, 24 Sep 2013 14:39:33 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Takao Indoh <indou.takao@...fujitsu.com>,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	kexec@...ts.infradead.org, alex.williamson@...hat.com,
	bhe@...hat.com
Subject: Re: [PATCH v2] intel-iommu: Quiesce devices before disabling IOMMU

On Tue, 2013-09-24 at 15:16 +0200, Joerg Roedel wrote:
> 
> I am not convinced that this is the right approach. If a device wasn't
> translated by VT-d in the old kernel doesn't mean it will not be
> translated in the new kernel. How about unconditionally resetting all
> PCI busses and/or functions here before IOMMU initialization proceeds?

Forget the IOMMU.

If a device is doing DMA in the old kernel, and *continues* doing DMA
under the new kernel, surely something ought to shut it down?

It's the generic kexec or machine_shutdown code which should be doing
this, not IOMMU code. *Especially* not Intel-specific IOMMU code. It
does not live here.

If anything, the IOMMU gives you a way to *survive* this kind of thing
and means that you might get away without quiescing devices when
otherwise you would have died.

-- 
dwmw2

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