[PATCH v3 07/41] clocksource: hyper-v: Register sched_clock save/restore iff it's necessary

[Sean Christopherson <seanjc@xxxxxxxxxx>]

Register the Hyper-V reference counter (refcounter) callbacks for saving
and restoring its PV sched_clock, if and only if the refcounter is
actually being used for sched_clock.  Currently, Hyper-V overrides the
save/restore hooks if the reference TSC available, whereas the Hyper-V
refcounter code only overrides sched_clock if the reference TSC is
available *and* it's not invariant.  The flaw is effectively papered over
by invoking the "old" save/restore callbacks as part of save/restore, but
that's unnecessary and fragile.

To avoid introducing more complexity, and to allow for additional cleanups
of the PV sched_clock code, move the save/restore hooks and logic into
hyperv_timer.c and simply wire up the hooks when overriding sched_clock
itself.

Note, while the Hyper-V refcounter code is intended to be architecture
neutral, CONFIG_PARAVIRT is firmly x86-only, i.e. adding a small amount of
x86 specific code (which will be reduced in future cleanups) doesn't
meaningfully pollute generic code.

Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
Tested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/mshyperv.c     | 58 ------------------------------
 drivers/clocksource/hyperv_timer.c | 50 ++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 58 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 8d2401be420c..5ca139ae50b4 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -275,63 +275,6 @@ static void hv_guest_crash_shutdown(struct pt_regs *regs)
 }
 #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;
-}
-
 #ifdef CONFIG_X86_64
 DEFINE_STATIC_CALL(hv_hypercall, hv_std_hypercall);
 EXPORT_STATIC_CALL_TRAMP_GPL(hv_hypercall);
@@ -739,7 +682,6 @@ 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 e9f5034a1bc8..72b966340a46 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -537,10 +537,60 @@ static __always_inline void hv_setup_sched_clock(void 
*sched_clock)
 #elif defined CONFIG_PARAVIRT
 #include <asm/timer.h>
 
+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 __always_inline void hv_setup_sched_clock(void *sched_clock)
 {
        /* We're on x86/x64 *and* using PV ops */
        paravirt_set_sched_clock(sched_clock);
+
+       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;
 }
 #else /* !CONFIG_GENERIC_SCHED_CLOCK && !CONFIG_PARAVIRT */
 static __always_inline void hv_setup_sched_clock(void *sched_clock) {}
-- 
2.54.0.563.g4f69b47b94-goog