Commit e39acc37 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

clocksource: hyper-v: Provide noinstr sched_clock() 



With the intent to provide local_clock_noinstr(), a variant of
local_clock() that's safe to be called from noinstr code (with the
assumption that any such code will already be non-preemptible),
prepare for things by making the Hyper-V TSC and MSR sched_clock
implementations noinstr.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Co-developed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Signed-off-by: default avatarMichael Kelley <mikelley@microsoft.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>  # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.843039089@infradead.org
parent 9397fa2e

arch/x86/include/asm/mshyperv.h

+5 −0
Original line number Diff line number Diff line
@@ -257,6 +257,11 @@ void hv_set_register(unsigned int reg, u64 value); 
u64 hv_get_non_nested_register(unsigned int reg);

void hv_set_non_nested_register(unsigned int reg, u64 value);



static __always_inline u64 hv_raw_get_register(unsigned int reg)

{

	return __rdmsr(reg);

}



#else /* CONFIG_HYPERV */

static inline void hyperv_init(void) {}

static inline void hyperv_setup_mmu_ops(void) {}

drivers/clocksource/hyperv_timer.c

+18 −14
Original line number Diff line number Diff line
@@ -365,6 +365,20 @@ void hv_stimer_global_cleanup(void) 
}

EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);



static __always_inline u64 read_hv_clock_msr(void)

{

	/*

	 * Read the partition counter to get the current tick count. This count

	 * is set to 0 when the partition is created and is incremented in 100

	 * nanosecond units.

	 *

	 * Use hv_raw_get_register() because this function is used from

	 * noinstr. Notable; while HV_REGISTER_TIME_REF_COUNT is a synthetic

	 * register it doesn't need the GHCB path.

	 */

	return hv_raw_get_register(HV_REGISTER_TIME_REF_COUNT);

}



/*

 * Code and definitions for the Hyper-V clocksources.  Two

 * clocksources are defined: one that reads the Hyper-V defined MSR, and
@@ -393,7 +407,7 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void) 
}

EXPORT_SYMBOL_GPL(hv_get_tsc_page);



static notrace u64 read_hv_clock_tsc(void)

static __always_inline u64 read_hv_clock_tsc(void)

{

	u64 cur_tsc, time;
@@ -404,7 +418,7 @@ static notrace u64 read_hv_clock_tsc(void) 
	 * to the MSR in case the TSC page indicates unavailability.

	 */

	if (!hv_read_tsc_page_tsc(tsc_page, &cur_tsc, &time))

		time = hv_get_register(HV_REGISTER_TIME_REF_COUNT);

		time = read_hv_clock_msr();



	return time;

}
@@ -414,7 +428,7 @@ static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg) 
	return read_hv_clock_tsc();

}



static u64 notrace read_hv_sched_clock_tsc(void)

static u64 noinstr read_hv_sched_clock_tsc(void)

{

	return (read_hv_clock_tsc() - hv_sched_clock_offset) *

		(NSEC_PER_SEC / HV_CLOCK_HZ);
@@ -466,22 +480,12 @@ static struct clocksource hyperv_cs_tsc = { 
#endif

};



static u64 notrace read_hv_clock_msr(void)

{

	/*

	 * Read the partition counter to get the current tick count. This count

	 * is set to 0 when the partition is created and is incremented in

	 * 100 nanosecond units.

	 */

	return hv_get_register(HV_REGISTER_TIME_REF_COUNT);

}



static u64 notrace read_hv_clock_msr_cs(struct clocksource *arg)

{

	return read_hv_clock_msr();

}



static u64 notrace read_hv_sched_clock_msr(void)

static u64 noinstr read_hv_sched_clock_msr(void)

{

	return (read_hv_clock_msr() - hv_sched_clock_offset) *

		(NSEC_PER_SEC / HV_CLOCK_HZ);