Re: [PATCH v4 10/38] perf/x86: Support switch_guest_ctx interface

[Peter Zijlstra]

On Mon, Mar 24, 2025 at 05:30:50PM +0000, Mingwei Zhang wrote:
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> 
> Implement switch_guest_ctx interface for x86 PMU, switch PMI to dedicated
> KVM_GUEST_PMI_VECTOR at perf guest enter, and switch PMI back to
> NMI at perf guest exit.
> 
> Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> Tested-by: Yongwei Ma <yongwei.ma@xxxxxxxxx>
> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
>  arch/x86/events/core.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 8f218ac0d445..28161d6ff26d 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2677,6 +2677,16 @@ static bool x86_pmu_filter(struct pmu *pmu, int cpu)
>  	return ret;
>  }
>  
> +static void x86_pmu_switch_guest_ctx(bool enter, void *data)
> +{
> +	u32 guest_lvtpc = *(u32 *)data;
> +
> +	if (enter)
> +		apic_write(APIC_LVTPC, guest_lvtpc);
> +	else
> +		apic_write(APIC_LVTPC, APIC_DM_NMI);
> +}

This, why can't it use x86_pmu.guest_lvtpc here and call it a day? Why
is that argument passed around through the generic code only to get back
here?