PERF_CAP_FW_WRITES
if (host_pmu->version < 4 || !(host_perf_cap & PERF_CAP_FW_WRITES))
return (vcpu_get_perf_capabilities(vcpu) & PERF_CAP_FW_WRITES) != 0;
u64 perf_cap = PERF_CAP_FW_WRITES;