[PATCH v6 27/51] clocksource: hyper-v: Don't save/restore TSC offset when using HV sched_clock

Now that Hyper-V overrides the sched_clock save/restore hooks if and only
sched_clock itself is set to the Hyper-V reference counter, drop the
invocation of the "old" save/restore callbacks.  When the registration of
the PV sched_clock was done separately from overriding the save/restore
hooks, it was possible for Hyper-V to clobber the TSC save/restore
callbacks without actually switching to the Hyper-V refcounter.

Enabling a PV sched_clock is a one-way street, i.e. the kernel will never
revert to using TSC for sched_clock, and so there is no need to invoke the
TSC save/restore hooks (and if there was, it belongs in common PV code).

Reviewed-by: Michael Kelley <[email protected]>
Tested-by: Michael Kelley <[email protected]>
Reviewed-by: David Woodhouse <[email protected]>
Acked-by: Wei Liu <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
 drivers/clocksource/hyperv_timer.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index daa8cbfe61ee..220668207d19 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -544,9 +544,6 @@ static __always_inline void hv_setup_sched_clock(void *sched_clock)
 #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
@@ -556,8 +553,6 @@ static void (*old_restore_sched_clock_state)(void);
  */
 static void hv_save_sched_clock_state(void)
 {
-	old_save_sched_clock_state();
-
 	hv_ref_counter_at_suspend = hv_read_reference_counter();
 }
 
@@ -570,8 +565,6 @@ static void hv_restore_sched_clock_state(void)
 	 *                - reference counter (time) now.
 	 */
 	hv_sched_clock_offset -= (hv_ref_counter_at_suspend - hv_read_reference_counter());
-
-	old_restore_sched_clock_state();
 }
 
 static __always_inline void hv_setup_sched_clock(void *sched_clock)
@@ -579,10 +572,7 @@ 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 */
-- 
2.55.0.679.g6767b8d81c-goog