linux-kernel - Re: [RESEND PATCH] iommu/intel: Exclude devices using RMRRs from IOMMU API domains

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Date:	Fri, 13 Jun 2014 15:34:08 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	iommu@...ts.linux-foundation.org, chegu_vinod@...com,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] iommu/intel: Exclude devices using RMRRs from
 IOMMU API domains

On Thu, 2014-06-12 at 10:35 -0600, Alex Williamson wrote:
> The user of the IOMMU API domain expects to have full control of
> the IOVA space for the domain.  RMRRs are fundamentally incompatible
> with that idea.  We can neither map the RMRR into the IOMMU API
> domain, nor can we guarantee that the device won't continue DMA with
> the area described by the RMRR as part of the new domain.  Therefore
> we must prevent such devices from being used by the IOMMU API.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
> 
> I didn't see any actionable items from the last posting of this, so
> re-posting unchanged.

That also wants a Cc:stable, I suppose.

I note we now have two copies of the 'device has RMRR and we actually
care' logic, where the latter clause is really just "is it USB".

Is it worth consolidating that into a macro that's used in both places,
in case the check does get more complicated? Are other devices going to
start getting added to the class of "we don't need the RMRRs to persist
and we *do* want to be able to assign them"... or is that just
needlessly overcomplicating it at this stage?

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

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