From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tim Deegan <tim@xen.org>
Subject: Re: Superpages for VT-D
Date: Thu, 19 Jul 2012 11:23:26 +0100
Message-ID: <20120719102326.GC75169@ocelot.phlegethon.org>
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To: Santosh Jodh <Santosh.Jodh@citrix.com>
Cc: "jun.nakajima@intel.com" <jun.nakajima@intel.com>, "xiantao.zhang@intel.com" <xiantao.zhang@intel.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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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. 

Cheers,

Tim.