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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Abhinav Srivastava <abhinavs_iitkgp@xxxxxxxxxxx> 25.06.09 18:57 >>>
>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.

Not sure what you actually want to do: There are two possible patches you might 
be talking about: One was simply to add (command line triggerable) support for 
printing out LBR values during register dumps (i.e. in particular when Xen 
crashes - which it will never do ;-) ). The other was to allow HVM guests to 
enable LBR recording on their own.

>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.

If you refer to the second of the described patches, the guest has to do action 
on it own.

Jan


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