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Subject[PATCH V2 2/2] clocksource/Hyper-V: Add Hyper-V specific sched clock function
Date
From: Tianyu Lan <Tianyu.Lan@microsoft.com>

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.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
arch/x86/hyperv/hv_init.c | 2 --
arch/x86/kernel/cpu/mshyperv.c | 8 ++++++++
drivers/clocksource/hyperv_timer.c | 22 ++++++++++++----------
include/asm-generic/mshyperv.h | 1 +
4 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 0d258688c8cf..866dfb3dca48 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -301,8 +301,6 @@ void __init hyperv_init(void)

x86_init.pci.arch_init = hv_pci_init;

- /* Register Hyper-V specific clocksource */
- hv_init_clocksource();
return;

remove_cpuhp_state:
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 062f77279ce3..53afd33990eb 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -29,6 +29,7 @@
#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);
@@ -338,9 +339,16 @@ static void __init ms_hyperv_init_platform(void)
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 = {
.name = "Microsoft Hyper-V",
.detect = ms_hyperv_platform,
diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index 432aa331df04..dad8af198e20 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -215,6 +215,7 @@ EXPORT_SYMBOL_GPL(hyperv_cs);
#ifdef CONFIG_HYPERV_TSCPAGE

static struct ms_hyperv_tsc_page tsc_pg __aligned(PAGE_SIZE);
+static u64 hv_sched_clock_offset __ro_after_init;

struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
{
@@ -222,7 +223,7 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
}
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);

@@ -232,9 +233,9 @@ static u64 notrace read_hv_sched_clock_tsc(void)
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 = {
@@ -246,7 +247,7 @@ 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;
/*
@@ -258,9 +259,9 @@ static u64 notrace read_hv_sched_clock_msr(void)
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 = {
@@ -298,8 +299,9 @@ static bool __init hv_init_tsc_clocksource(void)
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
@@ -329,7 +331,7 @@ void __init hv_init_clocksource(void)
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);
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index 0becb7d9704d..18d8e2d8210f 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -167,6 +167,7 @@ void hyperv_report_panic(struct pt_regs *regs, long err);
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) {}
--
2.14.5
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