Re: [RFC PATCH 28/41] KVM: x86/pmu: Switch IA32_PERF_GLOBAL_CTRL at VM boundary

[Sean Christopherson]

On Fri, Jan 26, 2024, Xiong Zhang wrote:
> +static void save_perf_global_ctrl_in_passthrough_pmu(struct vcpu_vmx *vmx)
> +{
> +	struct kvm_pmu *pmu = vcpu_to_pmu(&vmx->vcpu);
> +	int i;
> +
> +	if (vm_exit_controls_get(vmx) & VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL) {
> +		pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
> +	} else {
> +		i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore.guest,
> +						MSR_CORE_PERF_GLOBAL_CTRL);
> +		if (i < 0)
> +			return;
> +		pmu->global_ctrl = vmx->msr_autostore.guest.val[i].value;

As before, NAK to using the MSR load/store lists unless there's a *really* good
reason I'm missing.

And we should consider adding VCPU_EXREG_GLOBAL_CTRL so that we can defer the
VMREAD until KVM actually tries to access the guest value.