Messages in this thread | | | Date | Mon, 28 Mar 2022 19:12:45 +0200 | Subject | Re: [PATCH v4 2/6] KVM: x86: nSVM: implement nested LBR virtualization | From | Paolo Bonzini <> |
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On 3/27/22 17:12, Maxim Levitsky wrote: > - with LBR virtualization supported, the guest can set this msr to any value > as long as it doesn't set reserved bits and then read back the written value, > but it is not used by the CPU, unless LBR bit is set in MSR_IA32_DEBUGCTLMSR, > because only then LBR virtualization is enabled, which makes the CPU > load the guest value on VM entry. > > This means that MSR_IA32_DEBUGCTLMSR.BTF will magically start working when > MSR_IA32_DEBUGCTLMSR.LBR is set as well, and will not work otherwise.
That can be fixed by context-switching DEBUGCTLMSR by hand when LBR=0 && BTF=1. Would you like to give it a shot?
Paolo
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