From: Naman Jain namjain@linux.microsoft.com Sent: Monday, September 16, 2024 10:39 PM
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
- 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
Changes from v2: https://lore.kernel.org/all/20240911045632.3757-1-namjain@linux.microsoft.co... Addressed Michael's comments:
- Changed commit msg to include information on making timestamps continuous
- Changed subject to reflect the new file being changed
- Changed variable name for saving offset/counters
- Moved comment on new function introduced from header file to function definition.
- Removed the equations in comments
- Rebased to latest linux-next tip
Changes from v1: https://lore.kernel.org/all/20240909053923.8512-1-namjain@linux.microsoft.co...
- Reorganized code as per Michael's comment, and moved the logic to x86
specific files, to keep hyperv_timer.c arch independent.
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(-)
This all looks good to me now. Thanks for indulging all my comments. :-)
One minor nit: The "Subject:" prefix should not have a dash in "hyper-v". The goal is to be consistent in the prefixes used for a particular file instead of wandering all over the place. If you check the commit history for arch/x86/kernel/cpu/mshyperv.c, you'll see that it is "x86/hyperv", not "x86/hyperv-v".
This is super picky, so don't respin just for this. The maintainer can probably fix it when accepting the patch if there are no other changes.
Reviewed-by: Michael Kelley mhklinux@outlook.com
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index ead967479fa6..e8e25d6e64cd 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -224,6 +224,63 @@ static void hv_machine_crash_shutdown(struct pt_regs *regs) hyperv_cleanup(); } #endif /* CONFIG_CRASH_DUMP */
+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) @@ -590,6 +647,7 @@ static void __init ms_hyperv_init_platform(void)
/* Register Hyper-V specific clocksource */ hv_init_clocksource();
- x86_setup_ops_for_tsc_pg_clock(); hv_vtl_init_platform();
#endif /* diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index 99177835cade..b39dee7b93af 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
@@ -470,6 +471,17 @@ static void resume_hv_clock_tsc(struct clocksource *arg) hv_set_msr(HV_MSR_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 6cdc873ac907..aa5233b1eba9 100644 --- a/include/clocksource/hyperv_timer.h +++ b/include/clocksource/hyperv_timer.h @@ -38,6 +38,8 @@ extern void hv_remap_tsc_clocksource(void); extern unsigned long hv_get_tsc_pfn(void); extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
+extern void hv_adj_sched_clock_offset(u64 offset);
static __always_inline bool hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
base-commit: a430d95c5efa2b545d26a094eb5f624e36732af0
2.34.1