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charset="utf-8" PMU MSRs are set by QEMU only at levels >=3D KVM_PUT_RESET_STATE, excluding runtime. Therefore, updating these MSRs without stopping events should be acceptable. In addition, KVM creates kernel perf events with host mode excluded (exclude_host =3D 1). While the events remain active, they don't increment the counter during QEMU vCPU userspace mode. Finally, The kvm_put_msrs() sets the MSRs using KVM_SET_MSRS. The x86 KVM processes these MSRs one by one in a loop, only saving the config and triggering the KVM_REQ_PMU request. This approach does not immediately stop the event before updating PMC. This approach is true since Linux kernel commit 68fb4757e867 ("KVM: x86/pmu: Defer reprogram_counter() to kvm_pmu_handle_event"), that is, v6.2. No Fixed tag is going to be added for the commit 0d89436786b0 ("kvm: migrate vPMU state"), because this isn't a bugfix. Signed-off-by: Dongli Zhang Reviewed-by: Zhao Liu Reviewed-by: Dapeng Mi --- Changed since v3: - Re-order reasons in commit messages. - Mention KVM's commit 68fb4757e867 (v6.2). - Keep Zhao's review as there isn't code change. target/i386/kvm/kvm.c | 9 --------- 1 file changed, 9 deletions(-) diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 4bbdf996ef..207de21404 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -4186,13 +4186,6 @@ static int kvm_put_msrs(X86CPU *cpu, int level) } =20 if ((IS_INTEL_CPU(env) || IS_ZHAOXIN_CPU(env)) && pmu_version > 0)= { - if (pmu_version > 1) { - /* Stop the counter. */ - kvm_msr_entry_add(cpu, MSR_CORE_PERF_FIXED_CTR_CTRL, 0); - kvm_msr_entry_add(cpu, MSR_CORE_PERF_GLOBAL_CTRL, 0); - } - - /* Set the counter values. */ for (i =3D 0; i < num_pmu_fixed_counters; i++) { kvm_msr_entry_add(cpu, MSR_CORE_PERF_FIXED_CTR0 + i, env->msr_fixed_counters[i]); @@ -4208,8 +4201,6 @@ static int kvm_put_msrs(X86CPU *cpu, int level) env->msr_global_status); kvm_msr_entry_add(cpu, MSR_CORE_PERF_GLOBAL_OVF_CTRL, env->msr_global_ovf_ctrl); - - /* Now start the PMU. */ kvm_msr_entry_add(cpu, MSR_CORE_PERF_FIXED_CTR_CTRL, env->msr_fixed_ctr_ctrl); kvm_msr_entry_add(cpu, MSR_CORE_PERF_GLOBAL_CTRL, --=20 2.43.5