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LbrExtV2, introduced on Zen 4, is a branch sampling facility providing a 16-entry stack of last-taken branches via dedicated MSRs: * MSR 0xC000010E - Last Branch Stack Select (LBR_SELECT) * MSR 0xC000010F - Debug Extension Control (DBG_EXTN_CFG) * MSR 0xC0010300..0xC001031F - 16 LBR FROM/TO MSR pairs AMD hardware extends the VMCB save area with fields for these MSRs. When V_LBR (VMCB.MISC_CTL2.LBR_VIRTUALIZATION_ENABLE) is set, the CPU saves and restores the guest's LbrExtV2 state on VMRUN/#VMEXIT, letting the guest use LBR v2 without being intercepted. V_LBR is enabled lazily, i.e, LBR virtualization is enabled only when guest flips the DbgExtnCfg.LBRv2En (bit 6) to record branches. This is done to prevent MSR save/restore cost during VMRUN/#VMEXIT cycles when V_LBR is disabled. The dependent LBR and PMC freeze-on-PMI feature is added on top. Testing must be done by first disabling NMI watchdog on the host machine, and enabling the Mediated PMU framework. $ echo 0 | sudo tee /proc/sys/kernel/nmi_watchdog $ sudo modprobe kvm_amd enable_mediated_pmu=1 Regards, Shivansh --- Sandipan Das (1): KVM: SVM: Add VMCB fields for LBR v2 virtualization Shivansh Dhiman (6): KVM: SVM: Add capability for LbrExtV2 KVM: SVM: Emulate guest accesses to LBR v2 MSRs KVM: SVM: Enable hardware-assisted LBR v2 virtualization KVM: SVM: Advertise LbrExtV2 to userspace KVM: SVM: Add LBR/PMC freeze support KVM: x86: Use SCATTERED_F() for PERFMON_V2 arch/x86/events/core.c | 1 + arch/x86/include/asm/perf_event.h | 1 + arch/x86/include/asm/svm.h | 16 +++- arch/x86/kvm/cpuid.c | 9 +- arch/x86/kvm/reverse_cpuid.h | 6 +- arch/x86/kvm/svm/svm.c | 140 +++++++++++++++++++++++++++++- arch/x86/kvm/svm/svm.h | 7 +- 7 files changed, 172 insertions(+), 8 deletions(-) base-commit: 50406d35f5635e1cc523e61409d57e851b5f5df8 -- 2.43.0