Re: [PATCH v3 15/41] x86/xen/time: Nullify x86_platform's sched_clock save/restore hooks

[David Woodhouse]

On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote:
> Nullify the x86_platform sched_clock save/restore hooks when setting up
> Xen's PV clock to make it somewhat obvious the hooks aren't used when
> running as a Xen guest (Xen uses a paravirtualized suspend/resume flow).
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Hm. Xen HVM guests *do* use a standard ACPI S4 hibernation flow.

Does that need testing?

> ---
>  arch/x86/xen/time.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 3d3165eef821..21d366d01985 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -568,6 +568,12 @@ static void __init xen_init_time_common(void)
>  	xen_sched_clock_offset = xen_clocksource_read();
>  	static_call_update(pv_steal_clock, xen_steal_clock);
>  	paravirt_set_sched_clock(xen_sched_clock);
> +	/*
> +	 * Xen has paravirtualized suspend/resume and so doesn't use the common
> +	 * x86 sched_clock save/restore hooks.
> +	 */
> +	x86_platform.save_sched_clock_state = NULL;
> +	x86_platform.restore_sched_clock_state = NULL;
>  
>  	tsc_register_calibration_routines(xen_tsc_khz, NULL);
>  	x86_platform.get_wallclock = xen_get_wallclock;

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