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Re: [Xen-devel] [PATCH] AMD IOMMU: Defer IO pagetable construction until

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] AMD IOMMU: Defer IO pagetable construction until device assignment
From: Wei Wang2 <wei.wang2@xxxxxxx>
Date: Fri, 04 Apr 2008 14:34:34 +0200
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Retry for comment, Thanks!

During HVM domain creation, I/O page tables are filled by coping p2m
entries from p2m table, which is a useless step for non-passthru domain.
This patch defers I/O page table construction until the moment of device
assignment. In case that pci devices are never assigned or hot plugged,
the unnecessary duplication will be avoid. 


Signed-off-by: Wei Wang <wei.wang2@xxxxxxx>
AMD Saxony, Dresden, Germany
Operating System Research Center

Legal Information:
AMD Saxony Limited Liability Company & Co. KG
Sitz (Geschäftsanschrift):
   Wilschdorfer Landstr. 101, 01109 Dresden, Deutschland
Registergericht Dresden: HRA 4896
vertretungsberechtigter Komplementär:
   AMD Saxony LLC (Sitz Wilmington, Delaware, USA)
Geschäftsführer der AMD Saxony LLC:
   Dr. Hans-R. Deppe, Thomas McCoy 

On Wed, 2008-04-02 at 16:26 +0100, Keir Fraser wrote: 
> On 2/4/08 16:25, "Wei Wang2" <wei.wang2@xxxxxxx> wrote:
> >> I think you should leave p2m.c as it is, and then synchronise on creation 
> >> of
> >> the iommu tables from within amd_iommu_map_page(). You already have a
> >> mapping_lock in there which might do the trick.
> > I will update it. Maybe I need a new flag to indicate that I/O page tables 
> > has
> > been synchronised..
> Set and checked under the mapping lock. Yes, that would indeed work.
>  -- Keir

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