read_hv_sched_clock_tsc() assumes that the Hyper-V clock counter is bigger than the variable hv_sched_clock_offset, which is cached during early boot, but depending on the timing this assumption may be false when a hibernated VM starts again (the clock counter starts from 0 again) and is resuming back (Note: hv_init_tsc_clocksource() is not called during hibernation/resume); consequently, read_hv_sched_clock_tsc() may return a negative integer (which is interpreted as a huge positive integer since the return type is u64) and new kernel messages are prefixed with huge timestamps before read_hv_sched_clock_tsc() grows big enough (which typically takes several seconds).
Fix the issue by saving the Hyper-V clock counter just before the suspend, and using it to correct the hv_sched_clock_offset in resume. This makes hv tsc page based sched_clock continuous and ensures that post resume, it starts from where it left off during suspend. Override x86_platform.save_sched_clock_state and x86_platform.restore_sched_clock_state routines to correct this as soon as possible.
Note: if Invariant TSC is available, the issue doesn't happen because 1) we don't register read_hv_sched_clock_tsc() for sched clock: See commit e5313f1c5404 ("clocksource/drivers/hyper-v: Rework clocksource and sched clock setup"); 2) the common x86 code adjusts TSC similarly: see __restore_processor_state() -> tsc_verify_tsc_adjust(true) and x86_platform.restore_sched_clock_state().
Cc: stable@vger.kernel.org Fixes: 1349401ff1aa ("clocksource/drivers/hyper-v: Suspend/resume Hyper-V clocksource for hibernation") Co-developed-by: Dexuan Cui decui@microsoft.com Signed-off-by: Dexuan Cui decui@microsoft.com Signed-off-by: Naman Jain namjain@linux.microsoft.com Reviewed-by: Michael Kelley mhklinux@outlook.com Link: https://lore.kernel.org/r/20240917053917.76787-1-namjain@linux.microsoft.com Signed-off-by: Wei Liu wei.liu@kernel.org Message-ID: 20240917053917.76787-1-namjain@linux.microsoft.com (cherry picked from commit bcc80dec91ee745b3d66f3e48f0ec2efdea97149) Signed-off-by: Naman Jain namjain@linux.microsoft.com --- arch/x86/kernel/cpu/mshyperv.c | 58 ++++++++++++++++++++++++++++++ drivers/clocksource/hyperv_timer.c | 14 +++++++- include/clocksource/hyperv_timer.h | 2 ++ 3 files changed, 73 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index 542b818c0d20..6090fe513d40 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -152,6 +152,63 @@ static void hv_machine_crash_shutdown(struct pt_regs *regs) hyperv_cleanup(); } #endif /* CONFIG_KEXEC_CORE */ + +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 + * before suspend. This is to make sure that sched_clock using hv tsc page + * based clocksource, proceeds from where it left off during suspend and + * it shows correct time for the timestamps of kernel messages after resume. + */ +static void save_hv_clock_tsc_state(void) +{ + hv_ref_counter_at_suspend = hv_read_reference_counter(); +} + +static void restore_hv_clock_tsc_state(void) +{ + /* + * Adjust the offsets used by hv tsc clocksource to + * account for the time spent before hibernation. + * adjusted value = reference counter (time) at suspend + * - reference counter (time) now. + */ + hv_adj_sched_clock_offset(hv_ref_counter_at_suspend - hv_read_reference_counter()); +} + +/* + * Functions to override save_sched_clock_state and restore_sched_clock_state + * functions of x86_platform. The Hyper-V clock counter is reset during + * suspend-resume and the offset used to measure time needs to be + * corrected, post resume. + */ +static void hv_save_sched_clock_state(void) +{ + old_save_sched_clock_state(); + save_hv_clock_tsc_state(); +} + +static void hv_restore_sched_clock_state(void) +{ + restore_hv_clock_tsc_state(); + old_restore_sched_clock_state(); +} + +static void __init x86_setup_ops_for_tsc_pg_clock(void) +{ + if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE)) + return; + + 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; +} #endif /* CONFIG_HYPERV */
static uint32_t __init ms_hyperv_platform(void) @@ -454,6 +511,7 @@ static void __init ms_hyperv_init_platform(void)
/* Register Hyper-V specific clocksource */ hv_init_clocksource(); + x86_setup_ops_for_tsc_pg_clock(); #endif /* * TSC should be marked as unstable only after Hyper-V diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index 18de1f439ffd..6b4f58ee66e0 100644 --- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c @@ -27,7 +27,8 @@ #include <asm/mshyperv.h>
static struct clock_event_device __percpu *hv_clock_event; -static u64 hv_sched_clock_offset __ro_after_init; +/* Note: offset can hold negative values after hibernation. */ +static u64 hv_sched_clock_offset __read_mostly;
/* * If false, we're using the old mechanism for stimer0 interrupts @@ -417,6 +418,17 @@ static void resume_hv_clock_tsc(struct clocksource *arg) hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64); }
+/* + * Called during resume from hibernation, from overridden + * x86_platform.restore_sched_clock_state routine. This is to adjust offsets + * used to calculate time for hv tsc page based sched_clock, to account for + * time spent before hibernation. + */ +void hv_adj_sched_clock_offset(u64 offset) +{ + hv_sched_clock_offset -= offset; +} + #ifdef HAVE_VDSO_CLOCKMODE_HVCLOCK static int hv_cs_enable(struct clocksource *cs) { diff --git a/include/clocksource/hyperv_timer.h b/include/clocksource/hyperv_timer.h index b3f5d73ae1d6..6668e92b1cc4 100644 --- a/include/clocksource/hyperv_timer.h +++ b/include/clocksource/hyperv_timer.h @@ -34,6 +34,8 @@ extern void hv_init_clocksource(void);
extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
+extern void hv_adj_sched_clock_offset(u64 offset); + static inline notrace u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc) {