On Fri, Jan 26, 2024, Xiong Zhang wrote:
> + if (is_passthrough_pmu_enabled(&vmx->vcpu)) {
> + /*
> + * Setup auto restore guest PERF_GLOBAL_CTRL MSR at vm entry.
> + */
> + if (vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL)
> + vmcs_write64(GUEST_IA32_PERF_GLOBAL_CTRL, 0);
> + else {
> + i = vmx_find_loadstore_msr_slot(&vmx->msr_autoload.guest,
> + MSR_CORE_PERF_GLOBAL_CTRL);
> + if (i < 0) {
> + i = vmx->msr_autoload.guest.nr++;
> + vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT,
> + vmx->msr_autoload.guest.nr);
> + }
> + vmx->msr_autoload.guest.val[i].index = MSR_CORE_PERF_GLOBAL_CTRL;
> + vmx->msr_autoload.guest.val[i].value = 0;
Eww, no. Just make cpu_has_load_perf_global_ctrl() and VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL
hard requirements for enabling passthrough mode. And then have clear_atomic_switch_msr()
yell if KVM tries to disable loading MSR_CORE_PERF_GLOBAL_CTRL.
