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[Xen-devel] Last Branch Record (LBR) in Xen

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: Abhinav Srivastava <abhinavs_iitkgp@xxxxxxxxxxx>
  • Date: Thu, 25 Jun 2009 22:27:15 +0530 (IST)
  • Delivery-date: Thu, 25 Jun 2009 09:58:10 -0700
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Hi there,

I am trying to achieve Last Branch Recording (LBR) functionality on Intel Core 
2 Quad processor from Xen hypervisor. However, I could not get it working. I am 
using Xen-3.2.2 (which I agree is a bit old, however, there is not much change 
in the code related to this functionality in Xen-3.4).

I looked into the patch provided by Keir and Jan Beulich, and still I did not 
understand how to make it work. I got some success in creating single step on 
branch feature by setting bit 1 of GUEST_DEBUGCTL_MSR register. However, when I 
am trying to achieve LBR functionality (which requires reading LASTBRANCH_TO_IP 
and LASTBRANC_FROM_IP registers too), it is not working.

I must admit that by looking into the patch I got little bit confused. It would 
be really good if someone could tell me what are the steps required in the 
hypervisor to enable this feature. Since I want to control this feature from 
the hypervisor without doing anything inside guest, how should I approach to 
this problem.

Any help in this regard would be appreciated.


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