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

Michael Kelley
2020-12-17T17:32:43Z

From: Juergen Gross <jgross@suse.com> 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@suse.com>
> ---
> 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