clocksource/drivers/hyperv: Add Hyper-V specific sched clock function

Hyper-V guests use the default native_sched_clock() in
pv_ops.time.sched_clock on x86. But native_sched_clock() directly uses the
raw TSC value, which can be discontinuous in a Hyper-V VM.

Add the generic hv_setup_sched_clock() to set the sched clock function
appropriately. On x86, this sets pv_ops.time.sched_clock to read the
Hyper-V reference TSC value that is scaled and adjusted to be continuous.

Also move the Hyper-V reference TSC initialization much earlier in the boot
process so no discontinuity is observed when pv_ops.time.sched_clock
calculates its offset.

[ tglx: Folded build fix ]

Signed-off-by: Tianyu Lan <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Michael Kelley <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/hyperv/hv_init.c

···
 
 	x86_init.pci.arch_init = hv_pci_init;
 
-	/* Register Hyper-V specific clocksource */
-	hv_init_clocksource();
 	return;
 
 remove_cpuhp_state:

arch/x86/kernel/cpu/mshyperv.c

···
 #include <asm/timer.h>
 #include <asm/reboot.h>
 #include <asm/nmi.h>
+#include <clocksource/hyperv_timer.h>
 
 struct ms_hyperv_info ms_hyperv;
 EXPORT_SYMBOL_GPL(ms_hyperv);
···
 		x2apic_phys = 1;
 # endif
 
+	/* Register Hyper-V specific clocksource */
+	hv_init_clocksource();
 #endif
+}
+
+void hv_setup_sched_clock(void *sched_clock)
+{
+	pv_ops.time.sched_clock = sched_clock;
 }
 
 const __initconst struct hypervisor_x86 x86_hyper_ms_hyperv = {

drivers/clocksource/hyperv_timer.c

···
 #include <asm/mshyperv.h>
 
 static struct clock_event_device __percpu *hv_clock_event;
+static u64 hv_sched_clock_offset __ro_after_init;
 
 /*
  * If false, we're using the old mechanism for stimer0 interrupts
···
 }
 EXPORT_SYMBOL_GPL(hv_get_tsc_page);
 
-static u64 notrace read_hv_sched_clock_tsc(void)
+static u64 notrace read_hv_clock_tsc(struct clocksource *arg)
 {
 	u64 current_tick = hv_read_tsc_page(&tsc_pg);
 
···
 	return current_tick;
 }
 
-static u64 read_hv_clock_tsc(struct clocksource *arg)
+static u64 read_hv_sched_clock_tsc(void)
 {
-	return read_hv_sched_clock_tsc();
+	return read_hv_clock_tsc(NULL) - hv_sched_clock_offset;
 }
 
 static struct clocksource hyperv_cs_tsc = {
···
 };
 #endif
 
-static u64 notrace read_hv_sched_clock_msr(void)
+static u64 notrace read_hv_clock_msr(struct clocksource *arg)
 {
 	u64 current_tick;
 	/*
···
 	return current_tick;
 }
 
-static u64 read_hv_clock_msr(struct clocksource *arg)
+static u64 read_hv_sched_clock_msr(void)
 {
-	return read_hv_sched_clock_msr();
+	return read_hv_clock_msr(NULL) - hv_sched_clock_offset;
 }
 
 static struct clocksource hyperv_cs_msr = {
···
 	hv_set_clocksource_vdso(hyperv_cs_tsc);
 	clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
 
-	/* sched_clock_register is needed on ARM64 but is a no-op on x86 */
-	sched_clock_register(read_hv_sched_clock_tsc, 64, HV_CLOCK_HZ);
+	hv_sched_clock_offset = hyperv_cs->read(hyperv_cs);
+	hv_setup_sched_clock(read_hv_sched_clock_tsc);
+
 	return true;
 }
 #else
···
 	hyperv_cs = &hyperv_cs_msr;
 	clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
 
-	/* sched_clock_register is needed on ARM64 but is a no-op on x86 */
-	sched_clock_register(read_hv_sched_clock_msr, 64, HV_CLOCK_HZ);
+	hv_sched_clock_offset = hyperv_cs->read(hyperv_cs);
+	hv_setup_sched_clock(read_hv_sched_clock_msr);
 }
 EXPORT_SYMBOL_GPL(hv_init_clocksource);

include/asm-generic/mshyperv.h

···
 void hyperv_report_panic_msg(phys_addr_t pa, size_t size);
 bool hv_is_hyperv_initialized(void);
 void hyperv_cleanup(void);
+void hv_setup_sched_clock(void *sched_clock);
 #else /* CONFIG_HYPERV */
 static inline bool hv_is_hyperv_initialized(void) { return false; }
 static inline void hyperv_cleanup(void) {}