--- /dev/null
+From bcc80dec91ee745b3d66f3e48f0ec2efdea97149 Mon Sep 17 00:00:00 2001
+From: Naman Jain <namjain@linux.microsoft.com>
+Date: Tue, 17 Sep 2024 11:09:17 +0530
+Subject: x86/hyperv: Fix hv tsc page based sched_clock for hibernation
+
+From: Naman Jain <namjain@linux.microsoft.com>
+
+commit bcc80dec91ee745b3d66f3e48f0ec2efdea97149 upstream.
+
+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>
+Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ 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(-)
+
+--- a/arch/x86/kernel/cpu/mshyperv.c
++++ b/arch/x86/kernel/cpu/mshyperv.c
+@@ -163,6 +163,63 @@ static void hv_machine_crash_shutdown(st
+ 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)
+@@ -380,6 +437,7 @@ static void __init ms_hyperv_init_platfo
+
+ /* 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
+--- a/drivers/clocksource/hyperv_timer.c
++++ b/drivers/clocksource/hyperv_timer.c
+@@ -23,7 +23,8 @@
+ #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
+@@ -370,6 +371,17 @@ static void resume_hv_clock_tsc(struct c
+ hv_set_reference_tsc(tsc_msr);
+ }
+
++/*
++ * 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;
++}
++
+ static int hv_cs_enable(struct clocksource *cs)
+ {
+ hv_enable_vdso_clocksource();
+--- a/include/clocksource/hyperv_timer.h
++++ b/include/clocksource/hyperv_timer.h
+@@ -35,6 +35,8 @@ 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)
+ {
projects / thirdparty / kernel / stable-queue.git / commitdiff
