Last Branch Record (LBR) in Xen

[Abhinav Srivastava <abhinavs_iitkgp@yahoo.co.in>]

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.

Thanks,
Abhinav



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