On 15/10/2015 15:51, Jian Zhou wrote: > > > On 2015/10/14 19:30, Paolo Bonzini wrote: >> >> >> On 14/10/2015 13:26, Jian Zhou wrote: >>> On 12/10/2015 20:44, Paolo Bonzini wrote: >>>> In addition, the MSR numbers may differ between the guest and the host, >>>> because it is possible to emulate e.g. a Core CPU on a Core 2 CPU. >>>> So I >>>> recommend against using the atomic switch mechanism for the from/to >>>> MSRs. >>> >>> The vLBR feature depends on vPMU, and to enable vPMU, it needs to >>> specify the "cpu mode" in the guest XML as host-passthrough. I think >>> the MSR numbers between the guest and the host are the same in this >>> senario. >> >> Does it depend on vPMU _for Linux guests_ or in general? My impression >> is that LBR can be used by the guest independent of the PMU. > > I think only for Linux guests. > > I googled how to enable LBR on other guests(except Linux guests), > e.g. Windows, and got no developer manuals about it. > > Here is an article about it: > http://www.codeproject.com/Articles/517466/Last-branch-records- > and-branch-tracing > it says: > "bit 8 of DR7 represents bit 0 of DebugCtl. This is the LBR bit." Don't worry about the operating system in the guest: you are just emulating a processor feature, you do not care about anything except what is written in the Intel SDM. You can use kvm-unit-tests (https://git.kernel.org/cgit/virt/kvm/kvm-unit-tests.git/) to write a test for your feature. There are existing tests for debugging features. Thanks, Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
