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Re: [Xen-devel] Superpages for VT-D

Thanks Tim.

I understand the value of using superpages for IOMMU. What are the other 
advantages of sharing the table between the MMU and IOMMU (other than saving 
table memory)?


-----Original Message-----
From: Tim Deegan [mailto:tim@xxxxxxx] 
Sent: Thursday, July 19, 2012 3:23 AM
To: Santosh Jodh
Cc: xen-devel@xxxxxxxxxxxxx; xiantao.zhang@xxxxxxxxx; jun.nakajima@xxxxxxxxx
Subject: Re: [Xen-devel] Superpages for VT-D

At 09:18 -0700 on 13 Jul (1342171126), Santosh Jodh wrote:
> 1.       Are superpages (2MB, 1GB) enabled by default in Xen? If enabled, 
> what size?

Yes, they are enabled; for guest memory, Xen uses whatever the tools ask for, 
which (IIRC) is the largest available for HVM (falling back to smaller pages if 
no large ones can be found) and 2MB for PV if the guest supports PV superpages.

> 2.       On Intel, if superpages are enabled, is that used for the IOMMU?

Yes.  In fact the IOMMU code checks for IOMMU superpage support separately; if 
the IOMMU and the MMU have the same superpage sizes, they share a table; 
otherwise the p2m is duplicated in the IOMMU's format. 



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