Re: [RFC PATCH 06/41] perf: x86: Add function to switch PMI handler

[Sean Christopherson]

On Fri, Jan 26, 2024, Xiong Zhang wrote:
> From: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
> 
> Add function to switch PMI handler since passthrough PMU and host PMU will
> use different interrupt vectors.
> 
> Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
>  arch/x86/events/core.c            | 15 +++++++++++++++
>  arch/x86/include/asm/perf_event.h |  3 +++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 40ad1425ffa2..3f87894d8c8e 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -701,6 +701,21 @@ struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
>  }
>  EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
>  
> +void perf_guest_switch_to_host_pmi_vector(void)
> +{
> +	lockdep_assert_irqs_disabled();
> +
> +	apic_write(APIC_LVTPC, APIC_DM_NMI);
> +}
> +EXPORT_SYMBOL_GPL(perf_guest_switch_to_host_pmi_vector);
> +
> +void perf_guest_switch_to_kvm_pmi_vector(void)
> +{
> +	lockdep_assert_irqs_disabled();
> +
> +	apic_write(APIC_LVTPC, APIC_DM_FIXED | KVM_VPMU_VECTOR);
> +}
> +EXPORT_SYMBOL_GPL(perf_guest_switch_to_kvm_pmi_vector);

Why slice and dice the context switch if it's all in perf?  Just do this in
perf_guest_enter().