[PATCH v5 27/51] clocksource: hyper-v: Don't save/restore TSC offset when using HV sched_clock
From: Sean Christopherson <seanjc@google.com>
Date: 2026-07-01 19:33:00
Also in:
kvm, linux-coco, linux-doc, lkml, virtualization, xen-devel
Subsystem:
clocksource, clockevent drivers, hyper-v/azure core and drivers, the rest · Maintainers:
Daniel Lezcano, Thomas Gleixner, "K. Y. Srinivasan", Haiyang Zhang, Wei Liu, Dexuan Cui, Long Li, Linus Torvalds
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 <redacted> Tested-by: Michael Kelley <redacted> Reviewed-by: David Woodhouse <redacted> Acked-by: Wei Liu <wei.liu@kernel.org> Signed-off-by: Sean Christopherson <seanjc@google.com> --- 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.rc0.799.gd6f94ed593-goog