From 9397fa2ea3e7634f61da1ab76b9eb88ba04dfdfc Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 19 May 2023 12:21:07 +0200 Subject: clocksource: hyper-v: Adjust hv_read_tsc_page_tsc() to avoid special casing U64_MAX Currently hv_read_tsc_page_tsc() (ab)uses the (valid) time value of U64_MAX as an error return. This breaks the clean wrap-around of the clock. Modify the function signature to return a boolean state and provide another u64 pointer to store the actual time on success. This obviates the need to steal one time value and restores the full counter width. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Michael Kelley Tested-by: Michael Kelley # Hyper-V Link: https://lore.kernel.org/r/20230519102715.775630881@infradead.org --- drivers/clocksource/hyperv_timer.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) (limited to 'drivers/clocksource/hyperv_timer.c') diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index bcd9042a0c9f..c643bfe2f3d4 100644 --- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c @@ -393,14 +393,20 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void) } EXPORT_SYMBOL_GPL(hv_get_tsc_page); -static u64 notrace read_hv_clock_tsc(void) +static notrace u64 read_hv_clock_tsc(void) { - u64 current_tick = hv_read_tsc_page(hv_get_tsc_page()); + u64 cur_tsc, time; - if (current_tick == U64_MAX) - current_tick = hv_get_register(HV_REGISTER_TIME_REF_COUNT); + /* + * The Hyper-V Top-Level Function Spec (TLFS), section Timers, + * subsection Refererence Counter, guarantees that the TSC and MSR + * times are in sync and monotonic. Therefore we can fall back + * 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); - return current_tick; + return time; } static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg) -- cgit From e39acc37db34f6688e2c16e958fb1d662c422c81 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 19 May 2023 12:21:08 +0200 Subject: 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: Peter Zijlstra (Intel) Co-developed-by: Michael Kelley Signed-off-by: Michael Kelley Signed-off-by: Peter Zijlstra (Intel) Tested-by: Michael Kelley # Hyper-V Link: https://lore.kernel.org/r/20230519102715.843039089@infradead.org --- drivers/clocksource/hyperv_timer.c | 32 ++++++++++++++++++-------------- 1 file changed, 18 insertions(+), 14 deletions(-) (limited to 'drivers/clocksource/hyperv_timer.c') diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index c643bfe2f3d4..d851970e310c 100644 --- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c @@ -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); -- cgit