From: Sean Christopherson <seanjc@xxxxxxxxxx> Sent: Wednesday, February 26, 2025 6:18 PM
>
> Now that Hyper-V overrides the sched_clock save/restore hooks if and only
> sched_clock itself is set to the Hyper-V timer, drop the invocation of the
> "old" save/restore callbacks. When the registration of the PV sched_clock
> was done separate from overriding the save/restore hooks, it was possible
> for Hyper-V to clobber the TSC save/restore callbacks without actually
> switching to the Hyper-V timer.
Terminology again.
>
> Enabling a PV sched_clock is a one-way street, i.e. the kernel will never
> revert to using TSC for sched_clock, and so there is no need to invoke the
> TSC save/restore hooks (and if there was, it belongs in common PV code).
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
I've tested the full patch series in a Hyper-V guest on x86 with
and without the Hyper-V TSC_INVARIANT option. In both cases,
the sched_clock is correctly maintained across hibernation and
resume from hibernation, and the "flags" in /proc/cpuinfo are
as expected. I also compiled hyperv_timer.c on arm64, and that is
clean with no errors. So all is good.
Modulo the terminology used in the commit message,
Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
Tested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> ---
> drivers/clocksource/hyperv_timer.c | 10 ----------
> 1 file changed, 10 deletions(-)
>
> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> index 5a52d0acf31f..4a21874e91b9 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -524,9 +524,6 @@ static __always_inline void hv_setup_sched_clock(void
> *sched_clock)
> }
> #elif defined CONFIG_PARAVIRT
> static u64 hv_ref_counter_at_suspend;
> -static void (*old_save_sched_clock_state)(void);
> -static void (*old_restore_sched_clock_state)(void);
> -
> /*
> * Hyper-V clock counter resets during hibernation. Save and restore clock
> * offset during suspend/resume, while also considering the time passed
> @@ -536,8 +533,6 @@ static void (*old_restore_sched_clock_state)(void);
> */
> static void hv_save_sched_clock_state(void)
> {
> - old_save_sched_clock_state();
> -
> hv_ref_counter_at_suspend = hv_read_reference_counter();
> }
>
> @@ -550,8 +545,6 @@ static void hv_restore_sched_clock_state(void)
> * - reference counter (time) now.
> */
> hv_sched_clock_offset -= (hv_ref_counter_at_suspend - hv_read_reference_counter());
> -
> - old_restore_sched_clock_state();
> }
>
> static __always_inline void hv_setup_sched_clock(void *sched_clock)
> @@ -559,10 +552,7 @@ static __always_inline void hv_setup_sched_clock(void
> *sched_clock)
> /* We're on x86/x64 *and* using PV ops */
> paravirt_set_sched_clock(sched_clock);
>
> - old_save_sched_clock_state = x86_platform.save_sched_clock_state;
> x86_platform.save_sched_clock_state = hv_save_sched_clock_state;
> -
> - old_restore_sched_clock_state = x86_platform.restore_sched_clock_state;
> x86_platform.restore_sched_clock_state = hv_restore_sched_clock_state;
> }
> #else /* !CONFIG_GENERIC_SCHED_CLOCK && !CONFIG_PARAVIRT */
> --
> 2.48.1.711.g2feabab25a-goog
>
