Revert "x86/hyperv: Fix hv tsc page based sched_clock for hibernation"

This reverts commit 6681113633dc738ec95fe33104843a1e25acef3b which is
commit bcc80dec91ee745b3d66f3e48f0ec2efdea97149 upstream.

The dependant patch before this one caused build errors in the 6.6.y
tree, so revert this for now so that we can fix them up properly.

Reported-by: Ignat Korchagin <ignat@cloudflare.com>
Link: https://lore.kernel.org/r/3DB3A6D3-0D3A-4682-B4FA-407B2D3263B2@cloudflare.com
Reported-by: Lars Wendler <wendler.lars@web.de>
Link: https://lore.kernel.org/r/20250110103328.0e3906a8@chagall.paradoxon.rec
Reported-by: Chris Clayton <chris2553@googlemail.com>
Link: https://lore.kernel.org/r/10c7be00-b1f8-4389-801b-fb2d0b22468d@googlemail.com
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Naman Jain <namjain@linux.microsoft.com>
Cc: Michael Kelley <mhklinux@outlook.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 1 insertions, 73 deletions

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 6328cf56e59b..93e1cb4f7ff1 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -224,63 +224,6 @@ 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)
@@ -635,7 +578,6 @@ 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 5eec1457e139..8ff7cd4e20bb 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -27,8 +27,7 @@
 #include <asm/mshyperv.h>
 
 static struct clock_event_device __percpu *hv_clock_event;
-/* Note: offset can hold negative values after hibernation. */
-static u64 hv_sched_clock_offset __read_mostly;
+static u64 hv_sched_clock_offset __ro_after_init;
 
 /*
  * If false, we're using the old mechanism for stimer0 interrupts
@@ -457,17 +456,6 @@ 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 aa5233b1eba9..6cdc873ac907 100644
--- a/include/clocksource/hyperv_timer.h
+++ b/include/clocksource/hyperv_timer.h
@@ -38,8 +38,6 @@ 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)