RE: [PATCH v3 06/15] x86/paravirt: switch time pvops functions to use static_call()

[Michael Kelley <mikelley@xxxxxxxxxxxxx>]

From: Juergen Gross <jgross@xxxxxxxx> Sent: Thursday, December 17, 2020 1:31 AM

> The time pvops functions are the only ones left which might be
> used in 32-bit mode and which return a 64-bit value.
> 
> Switch them to use the static_call() mechanism instead of pvops, as
> this allows quite some simplification of the pvops implementation.
> 
> Due to include hell this requires to split out the time interfaces
> into a new header file.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  arch/x86/Kconfig                      |  1 +
>  arch/x86/include/asm/mshyperv.h       | 11 --------
>  arch/x86/include/asm/paravirt.h       | 14 ----------
>  arch/x86/include/asm/paravirt_time.h  | 38 +++++++++++++++++++++++++++
>  arch/x86/include/asm/paravirt_types.h |  6 -----
>  arch/x86/kernel/cpu/vmware.c          |  5 ++--
>  arch/x86/kernel/kvm.c                 |  3 ++-
>  arch/x86/kernel/kvmclock.c            |  3 ++-
>  arch/x86/kernel/paravirt.c            | 16 ++++++++---
>  arch/x86/kernel/tsc.c                 |  3 ++-
>  arch/x86/xen/time.c                   | 12 ++++-----
>  drivers/clocksource/hyperv_timer.c    |  5 ++--
>  drivers/xen/time.c                    |  3 ++-
>  kernel/sched/sched.h                  |  1 +
>  14 files changed, 71 insertions(+), 50 deletions(-)
>  create mode 100644 arch/x86/include/asm/paravirt_time.h
>

[snip]
 
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index ffc289992d1b..45942d420626 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -56,17 +56,6 @@ typedef int (*hyperv_fill_flush_list_func)(
>  #define hv_get_raw_timer() rdtsc_ordered()
>  #define hv_get_vector() HYPERVISOR_CALLBACK_VECTOR
> 
> -/*
> - * Reference to pv_ops must be inline so objtool
> - * detection of noinstr violations can work correctly.
> - */
> -static __always_inline void hv_setup_sched_clock(void *sched_clock)
> -{
> -#ifdef CONFIG_PARAVIRT
> -     pv_ops.time.sched_clock = sched_clock;
> -#endif
> -}
> -
>  void hyperv_vector_handler(struct pt_regs *regs);
> 
>  static inline void hv_enable_stimer0_percpu_irq(int irq) {}

[snip]

> diff --git a/drivers/clocksource/hyperv_timer.c 
> b/drivers/clocksource/hyperv_timer.c
> index ba04cb381cd3..1ed79993fc50 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -21,6 +21,7 @@
>  #include <clocksource/hyperv_timer.h>
>  #include <asm/hyperv-tlfs.h>
>  #include <asm/mshyperv.h>
> +#include <asm/paravirt_time.h>
> 
>  static struct clock_event_device __percpu *hv_clock_event;
>  static u64 hv_sched_clock_offset __ro_after_init;
> @@ -445,7 +446,7 @@ static bool __init hv_init_tsc_clocksource(void)
>       clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
> 
>       hv_sched_clock_offset = hv_read_reference_counter();
> -     hv_setup_sched_clock(read_hv_sched_clock_tsc);
> +     paravirt_set_sched_clock(read_hv_sched_clock_tsc);
> 
>       return true;
>  }
> @@ -470,6 +471,6 @@ void __init hv_init_clocksource(void)
>       clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
> 
>       hv_sched_clock_offset = hv_read_reference_counter();
> -     hv_setup_sched_clock(read_hv_sched_clock_msr);
> +     static_call_update(pv_sched_clock, read_hv_sched_clock_msr);
>  }
>  EXPORT_SYMBOL_GPL(hv_init_clocksource);

These Hyper-V changes are problematic as we want to keep hyperv_timer.c
architecture independent.  While only the code for x86/x64 is currently
accepted upstream, code for ARM64 support is in progress.   So we need
to use hv_setup_sched_clock() in hyperv_timer.c, and have the per-arch
implementation in mshyperv.h.

Michael