linux-kernel - Re: [PATCH] Xen-SWIOTBL v0.8.3 used for Xen PCI pass through for PV guests.

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Date:	Tue, 22 Jun 2010 15:23:25 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	linux-kernel@...r.kernel.org, fujita.tomonori@....ntt.co.jp,
	iommu@...ts.linux-foundation.org, albert_herranz@...oo.es,
	x86@...nel.org
Subject: Re: [PATCH] Xen-SWIOTBL v0.8.3 used for Xen PCI pass through for
 PV guests.

On Tue, 2010-06-22 at 15:42 -0400, Konrad Rzeszutek Wilk wrote:
> These nineteen patches lay the groundwork for Xen Paravirtualized (PV)
> domains to access PCI pass-through devices. These patches utilize the
> SWIOTLB library modifications (http://lkml.org/lkml/2010/6/4/272).
> 
> The end user of this is the Xen PCI frontend and Xen PCI [1] which
> require a DMA API "backend" that understands Xen's MMU. This allows the
> PV domains to use PCI devices.

Hi Konrad,

Sorry if I missed it, but I didn't see any mention or apparent
requirement of a hardware iommu in xen for this code.  Is that true?  If
so, is there anything to stop a PV guest with ownership of a DMA capable
PCI device from reading all sorts of memory that the domain wouldn't
otherwise have access to?  I was under the impression that the old PCI
front/back for PV guests was mainly an interesting hack with limited
applications due to security.  Thanks,

Alex

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