linux-kernel - Re: [PATCH 0/2] Introduce iommu

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Date:	Thu, 23 Jun 2011 18:21:37 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	David Woodhouse <dwmw2@...radead.org>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	David Brown <davidb@...eaurora.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>,
	Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH 0/2] Introduce iommu_commit() function

On Thu, Jun 23, 2011 at 11:38:54AM -0400, David Woodhouse wrote:
> On Thu, 2011-06-23 at 17:31 +0200, Joerg Roedel wrote:
> > David, I think especially VT-d can benefit from such a callback. I will
> > implement support for it in the AMD IOMMU driver and post a patch-set
> > soon.
> > 
> > Any comments, thoughts?
> 
> Ick. We *already* do the flushes as appropriate while we're filling the
> page tables. So every time we move on from one page table page to the
> next, we'll flush the old one. And when we've *done* filling the page
> tables for the range we've been asked to map, we flush the last writes
> too.

It doesn't sound too complicated to make this work with iommu_commit.
All the VT-d driver needs to do is to keep track of the last page-table
page a map/unmap request was targeted to (per domain). Subsequent
map/unmap calls check if the same page is targeted and flushes the old
one if not.  The last writes are flushed in the iommu_commit() call
(together with the IOMMU cache flushes).

It is basically the same algorithm you use now except that it works
accross iommu_map/iommu_unmap calls.

	Joerg

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