At 21:17 +0200 on 26 May (1369603037), enrico canzonieri
wrote:> Hi,
> currently I am working on Xen because I am very interested in
> virtualization technologies and I want to learn more about their
> hypervisors internals. I would like to contribute at Xen community as
> developer.
>
>
> Looking at Intel software developer''s manual I came across with
VMCS
> shadowing.
> I would understand when it is used in Xen and with what advantages.
> Is it really useful for nested virtualization?
Yes, it has been used in Xen, for nested virtualization, since January:
commit 15e64e205e121c1eb18b6a9c1953c82443e4cd5a
Author: Dongxiao Xu <dongxiao.xu@intel.com>
Date: Fri Jan 25 10:19:55 2013 +0100
nested vmx: enable VMCS shadowing feature
The current logic for handling the non-root VMREAD/VMWRITE is by
VM-Exit and emulate, which may bring certain overhead.
On new Intel platform, it introduces a new feature called VMCS
shadowing, where non-root VMREAD/VMWRITE will not trigger VM-Exit,
and the hardware will read/write the virtual VMCS instead.
This is proved to have performance improvement with the feature.
Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Acked-by: Jun Nakajima <jun.nakajima@intel.com>
Acked-by Eddie Dong <eddie.dong@intel.com>
Committed-by: Jan Beulich <jbeulich@suse.com>