Re: [PATCH 1/2] Drivers: hv: Move Hyper-V clockevents code to new clocksource driver

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Michael Kelley <mikelley@microsoft.com> writes:

> Clockevents code for Hyper-V synthetic timers is currently mixed
> in with other Hyper-V code. Move the code to a Hyper-V specific
> driver in the "clocksource" directory. Update the VMbus driver
> to call initialization and cleanup routines since the Hyper-V
> synthetic timers are not independently enumerated in ACPI.
>

I like the idea! Would it also make sense to consider moving Hyper-V
clocksource from arch/x86/hyperv/hv_init.c? The thing is that we use it
from arch-independent code (e.g. seee 'hyperv_cs' usage in
drivers/hv/hv_util.c).

> No behavior is changed and no new functionality is added.
>
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> ---
>  MAINTAINERS                           |   2 +
>  arch/x86/include/asm/hyperv-tlfs.h    |   6 +
>  arch/x86/kernel/cpu/mshyperv.c        |   2 +
>  drivers/clocksource/Makefile          |   1 +
>  drivers/clocksource/hyperv_syntimer.c | 206 ++++++++++++++++++++++++++++++++++
>  drivers/hv/hv.c                       | 154 -------------------------
>  drivers/hv/hyperv_vmbus.h             |   3 -
>  drivers/hv/vmbus_drv.c                |  39 +++----
>  include/clocksource/hyperv_syntimer.h |  26 +++++
>  9 files changed, 263 insertions(+), 176 deletions(-)
>  create mode 100644 drivers/clocksource/hyperv_syntimer.c
>  create mode 100644 include/clocksource/hyperv_syntimer.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 21ab064..3352716 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7159,6 +7159,7 @@ F:	arch/x86/include/asm/trace/hyperv.h
>  F:	arch/x86/include/asm/hyperv-tlfs.h
>  F:	arch/x86/kernel/cpu/mshyperv.c
>  F:	arch/x86/hyperv
> +F:	drivers/clocksource/hyperv_syntimer.c
>  F:	drivers/hid/hid-hyperv.c
>  F:	drivers/hv/
>  F:	drivers/input/serio/hyperv-keyboard.c
> @@ -7168,6 +7169,7 @@ F:	drivers/scsi/storvsc_drv.c
>  F:	drivers/uio/uio_hv_generic.c
>  F:	drivers/video/fbdev/hyperv_fb.c
>  F:	net/vmw_vsock/hyperv_transport.c
> +F:	include/clocksource/hyperv_syntimer.h

Nitpicking:

This has nothing to do with your patch but we have a mix of 'stimer',
'timer', 'syntimer' names when we refer to Hyper-V Synthetic timers, it
may make sense to try to converge on something (stimer would probably be
my personal preference but I don't really care as long as we use the
same abbreviation). Examples:

hv_init_timer_config(...)
HV_MSR_SYNTIMER_AVAILABLE
HYPERV_STIMER0_VECTOR
hv_syntimer_init(...)
...

>  F:	include/linux/hyperv.h
>  F:	include/uapi/linux/hyperv.h
>  F:	tools/hv/
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 2bdbbbc..ee62f57 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -401,6 +401,12 @@ enum HV_GENERIC_SET_FORMAT {
>  #define HV_STATUS_INVALID_CONNECTION_ID		18
>  #define HV_STATUS_INSUFFICIENT_BUFFERS		19
>  
> +/*
> + * The Hyper-V TimeRefCount register and the TSC
> + * page provide a guest VM clock with 100ns tick rate
> + */
> +#define HV_CLOCK_HZ (NSEC_PER_SEC/100)
> +
>  typedef struct _HV_REFERENCE_TSC_PAGE {
>  	__u32 tsc_sequence;
>  	__u32 res1;
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index e81a2db..f53a35a 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -21,6 +21,7 @@
>  #include <linux/irq.h>
>  #include <linux/kexec.h>
>  #include <linux/i8253.h>
> +#include <linux/random.h>
>  #include <asm/processor.h>
>  #include <asm/hypervisor.h>
>  #include <asm/hyperv-tlfs.h>
> @@ -84,6 +85,7 @@ __visible void __irq_entry hv_stimer0_vector_handler(struct pt_regs *regs)
>  	inc_irq_stat(hyperv_stimer0_count);
>  	if (hv_stimer0_handler)
>  		hv_stimer0_handler();
> +	add_interrupt_randomness(HYPERV_STIMER0_VECTOR, 0);
>  	ack_APIC_irq();
>  
>  	exiting_irq();
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index be6e0fb..a887955 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -83,3 +83,4 @@ obj-$(CONFIG_ATCPIT100_TIMER)		+= timer-atcpit100.o
>  obj-$(CONFIG_RISCV_TIMER)		+= timer-riscv.o
>  obj-$(CONFIG_CSKY_MP_TIMER)		+= timer-mp-csky.o
>  obj-$(CONFIG_GX6605S_TIMER)		+= timer-gx6605s.o
> +obj-$(CONFIG_HYPERV)			+= hyperv_syntimer.o

(just a couple of spare thoughs)

CONFIG_HYPERV can also be a module, are we OK with that? (we'll have to
support module loading/unloading then and honestly I see no reason for
that. I would prefer everything but VMBus devices to be in
kernel.) If we don't want it to be a module we can create a hidden
CONFIG_HYPERV_STIMER or something like that - just like we already do
for CONFIG_HYPERV_TSCPAGE.

There is, however, one additional dependency here: when running in
non-direct mode, Hyper-V clockevent devices require functional Hyper-V
messaging - which currently lives in VMBus code so that may explain why
you may want to keep stimer code in the same entity. Or, alternatively,
we can move Hyper-V messaging out of VMBus code (is it actually
architecture-agnostic?)

> diff --git a/drivers/clocksource/hyperv_syntimer.c b/drivers/clocksource/hyperv_syntimer.c
> new file mode 100644
> index 0000000..7276308
> --- /dev/null
> +++ b/drivers/clocksource/hyperv_syntimer.c
> @@ -0,0 +1,206 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Clocksource driver for the synthetic counter and timers
> + * provided by the Hyper-V hypervisor to guest VMs, as described
> + * in the Hyper-V Top Level Functional Spec (TLFS). This driver
> + * is instruction set architecture independent.
> + *
> + * Copyright (C) 2019, Microsoft, Inc.
> + *
> + * Author:  Michael Kelley <mikelley@microsoft.com>
> + */
> +
> +#include <linux/percpu.h>
> +#include <linux/cpumask.h>
> +#include <linux/clockchips.h>
> +#include <linux/cpuhotplug.h>
> +#include <linux/mm.h>
> +#include <clocksource/hyperv_syntimer.h>
> +#include <asm/hyperv-tlfs.h>
> +#include <asm/mshyperv.h>
> +
> +static struct clock_event_device __percpu *hv_clock_event;
> +
> +/*
> + * If false, we're using the old mechanism for stimer0 interrupts
> + * where it sends a VMbus message when it expires. The old
> + * mechanism is used when running on older versions of Hyper-V
> + * that don't support Direct Mode. While Hyper-V provides
> + * four stimer's per CPU, Linux uses only stimer0.
> + */
> +static bool direct_mode_enabled;
> +
> +static int stimer0_irq;
> +static int stimer0_vector;
> +static int stimer0_message_sint;
> +static int stimer0_cpuhp_online;
> +
> +/*
> + * ISR for when stimer0 is operating in Direct Mode.  Direct Mode
> + * does not use VMbus or any VMbus messages, so process here and not
> + * in the VMbus driver code.
> + */
> +void hv_stimer0_isr(void)
> +{
> +	struct clock_event_device *ce;
> +
> +	ce = this_cpu_ptr(hv_clock_event);
> +	ce->event_handler(ce);
> +}
> +EXPORT_SYMBOL_GPL(hv_stimer0_isr);
> +
> +static int hv_ce_set_next_event(unsigned long delta,
> +				struct clock_event_device *evt)
> +{
> +	u64 current_tick;
> +
> +	WARN_ON(!clockevent_state_oneshot(evt));
> +
> +	current_tick = hyperv_cs->read(NULL);
> +	current_tick += delta;
> +	hv_init_timer(0, current_tick);
> +	return 0;
> +}
> +
> +static int hv_ce_shutdown(struct clock_event_device *evt)
> +{
> +	hv_init_timer(0, 0);
> +	hv_init_timer_config(0, 0);
> +	if (direct_mode_enabled)
> +		hv_disable_stimer0_percpu_irq(stimer0_irq);
> +
> +	return 0;
> +}
> +
> +static int hv_ce_set_oneshot(struct clock_event_device *evt)
> +{
> +	union hv_stimer_config timer_cfg;
> +
> +	timer_cfg.as_uint64 = 0;
> +	timer_cfg.enable = 1;
> +	timer_cfg.auto_enable = 1;
> +	if (direct_mode_enabled) {
> +		/*
> +		 * When it expires, the timer will directly interrupt
> +		 * on the specified hardware vector/IRQ.
> +		 */
> +		timer_cfg.direct_mode = 1;
> +		timer_cfg.apic_vector = stimer0_vector;
> +		hv_enable_stimer0_percpu_irq(stimer0_irq);
> +	} else {
> +		/*
> +		 * When it expires, the timer will generate a VMbus message,
> +		 * to be handled by the normal VMbus interrupt handler.
> +		 */
> +		timer_cfg.direct_mode = 0;
> +		timer_cfg.sintx = stimer0_message_sint;
> +	}
> +	hv_init_timer_config(0, timer_cfg.as_uint64);
> +	return 0;
> +}
> +
> +/*
> + * hv_syntimer_init - Per-cpu initialization of the clockevent
> + */
> +static int hv_syntimer_init(unsigned int cpu)
> +{
> +	struct clock_event_device *ce;
> +
> +	if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE) {
> +		ce = per_cpu_ptr(hv_clock_event, cpu);
> +		ce->name = "Hyper-V clockevent";
> +		ce->features = CLOCK_EVT_FEAT_ONESHOT;
> +		ce->cpumask = cpumask_of(cpu);
> +		ce->rating = 1000;
> +		ce->set_state_shutdown = hv_ce_shutdown;
> +		ce->set_state_oneshot = hv_ce_set_oneshot;
> +		ce->set_next_event = hv_ce_set_next_event;
> +
> +		clockevents_config_and_register(ce,
> +						HV_CLOCK_HZ,
> +						HV_MIN_DELTA_TICKS,
> +						HV_MAX_MAX_DELTA_TICKS);
> +	}
> +	return 0;
> +}
> +
> +/*
> + * hv_syntimer_cleanup - Per-cpu cleanup of the clockevent
> + */
> +int hv_syntimer_cleanup(unsigned int cpu)
> +{
> +	struct clock_event_device *ce;
> +
> +	/* Turn off clockevent device */
> +	if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE) {
> +		ce = per_cpu_ptr(hv_clock_event, cpu);
> +		clockevents_unbind_device(ce, cpu);
> +		hv_ce_shutdown(ce);
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(hv_syntimer_cleanup);
> +
> +/* hv_syntimer_alloc - Global initialization of the clockevent and stimer0 */
> +int hv_syntimer_alloc(int sint)
> +{
> +	int	ret;
> +
> +	hv_clock_event = alloc_percpu(struct clock_event_device);
> +	if (!hv_clock_event)
> +		return -ENOMEM;
> +
> +	direct_mode_enabled = ms_hyperv.misc_features &
> +			HV_STIMER_DIRECT_MODE_AVAILABLE;
> +	if (direct_mode_enabled &&
> +	    hv_setup_stimer0_irq(&stimer0_irq, &stimer0_vector,
> +				hv_stimer0_isr))
> +		goto err_irq;
> +
> +	stimer0_message_sint = sint;
> +
> +	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "hyperv/stimer0:online",
> +				hv_syntimer_init, hv_syntimer_cleanup);
> +	if (ret < 0)
> +		goto err_cpuhp;
> +	stimer0_cpuhp_online = ret;
> +	return 0;
> +
> +err_cpuhp:
> +	if (direct_mode_enabled)
> +		hv_remove_stimer0_irq(stimer0_irq);
> +err_irq:
> +	free_percpu(hv_clock_event);
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL_GPL(hv_syntimer_alloc);
> +
> +/* hv_syntimer_free - Free global resources allocated by hv_syntimer_alloc() */
> +void hv_syntimer_free(void)
> +{
> +	cpuhp_remove_state(stimer0_cpuhp_online);
> +	if (direct_mode_enabled)
> +		hv_remove_stimer0_irq(stimer0_irq);
> +	free_percpu(hv_clock_event);
> +}
> +EXPORT_SYMBOL_GPL(hv_syntimer_free);
> +
> +/*
> + * Do a global cleanup of clockevents for the cases of kexec and
> + * vmbus exit
> + */
> +void hv_syntimer_global_cleanup(void)
> +{
> +	int	cpu;
> +	struct clock_event_device *ce;
> +
> +	if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE)
> +		for_each_present_cpu(cpu) {
> +			ce = per_cpu_ptr(hv_clock_event, cpu);
> +			clockevents_unbind_device(ce, cpu);
> +		}
> +	hv_syntimer_free();
> +}
> +EXPORT_SYMBOL_GPL(hv_syntimer_global_cleanup);
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 632d256..e3ee010 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -36,21 +36,6 @@
>  struct hv_context hv_context;
>  
>  /*
> - * If false, we're using the old mechanism for stimer0 interrupts
> - * where it sends a VMbus message when it expires. The old
> - * mechanism is used when running on older versions of Hyper-V
> - * that don't support Direct Mode. While Hyper-V provides
> - * four stimer's per CPU, Linux uses only stimer0.
> - */
> -static bool direct_mode_enabled;
> -static int stimer0_irq;
> -static int stimer0_vector;
> -
> -#define HV_TIMER_FREQUENCY (10 * 1000 * 1000) /* 100ns period */
> -#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
> -#define HV_MIN_DELTA_TICKS 1
> -
> -/*
>   * hv_init - Main initialization routine.
>   *
>   * This routine must be called before any other routines in here are called
> @@ -60,9 +45,6 @@ int hv_init(void)
>  	hv_context.cpu_context = alloc_percpu(struct hv_per_cpu_context);
>  	if (!hv_context.cpu_context)
>  		return -ENOMEM;
> -
> -	direct_mode_enabled = ms_hyperv.misc_features &
> -			HV_STIMER_DIRECT_MODE_AVAILABLE;
>  	return 0;
>  }
>  
> @@ -101,89 +83,6 @@ int hv_post_message(union hv_connection_id connection_id,
>  	return status & 0xFFFF;
>  }
>  
> -/*
> - * ISR for when stimer0 is operating in Direct Mode.  Direct Mode
> - * does not use VMbus or any VMbus messages, so process here and not
> - * in the VMbus driver code.
> - */
> -
> -static void hv_stimer0_isr(void)
> -{
> -	struct hv_per_cpu_context *hv_cpu;
> -
> -	hv_cpu = this_cpu_ptr(hv_context.cpu_context);
> -	hv_cpu->clk_evt->event_handler(hv_cpu->clk_evt);
> -	add_interrupt_randomness(stimer0_vector, 0);
> -}
> -
> -static int hv_ce_set_next_event(unsigned long delta,
> -				struct clock_event_device *evt)
> -{
> -	u64 current_tick;
> -
> -	WARN_ON(!clockevent_state_oneshot(evt));
> -
> -	current_tick = hyperv_cs->read(NULL);
> -	current_tick += delta;
> -	hv_init_timer(0, current_tick);
> -	return 0;
> -}
> -
> -static int hv_ce_shutdown(struct clock_event_device *evt)
> -{
> -	hv_init_timer(0, 0);
> -	hv_init_timer_config(0, 0);
> -	if (direct_mode_enabled)
> -		hv_disable_stimer0_percpu_irq(stimer0_irq);
> -
> -	return 0;
> -}
> -
> -static int hv_ce_set_oneshot(struct clock_event_device *evt)
> -{
> -	union hv_stimer_config timer_cfg;
> -
> -	timer_cfg.as_uint64 = 0;
> -	timer_cfg.enable = 1;
> -	timer_cfg.auto_enable = 1;
> -	if (direct_mode_enabled) {
> -		/*
> -		 * When it expires, the timer will directly interrupt
> -		 * on the specified hardware vector/IRQ.
> -		 */
> -		timer_cfg.direct_mode = 1;
> -		timer_cfg.apic_vector = stimer0_vector;
> -		hv_enable_stimer0_percpu_irq(stimer0_irq);
> -	} else {
> -		/*
> -		 * When it expires, the timer will generate a VMbus message,
> -		 * to be handled by the normal VMbus interrupt handler.
> -		 */
> -		timer_cfg.direct_mode = 0;
> -		timer_cfg.sintx = VMBUS_MESSAGE_SINT;
> -	}
> -	hv_init_timer_config(0, timer_cfg.as_uint64);
> -	return 0;
> -}
> -
> -static void hv_init_clockevent_device(struct clock_event_device *dev, int cpu)
> -{
> -	dev->name = "Hyper-V clockevent";
> -	dev->features = CLOCK_EVT_FEAT_ONESHOT;
> -	dev->cpumask = cpumask_of(cpu);
> -	dev->rating = 1000;
> -	/*
> -	 * Avoid settint dev->owner = THIS_MODULE deliberately as doing so will
> -	 * result in clockevents_config_and_register() taking additional
> -	 * references to the hv_vmbus module making it impossible to unload.
> -	 */
> -
> -	dev->set_state_shutdown = hv_ce_shutdown;
> -	dev->set_state_oneshot = hv_ce_set_oneshot;
> -	dev->set_next_event = hv_ce_set_next_event;
> -}
> -
> -
>  int hv_synic_alloc(void)
>  {
>  	int cpu;
> @@ -212,14 +111,6 @@ int hv_synic_alloc(void)
>  		tasklet_init(&hv_cpu->msg_dpc,
>  			     vmbus_on_msg_dpc, (unsigned long) hv_cpu);
>  
> -		hv_cpu->clk_evt = kzalloc(sizeof(struct clock_event_device),
> -					  GFP_KERNEL);
> -		if (hv_cpu->clk_evt == NULL) {
> -			pr_err("Unable to allocate clock event device\n");
> -			goto err;
> -		}
> -		hv_init_clockevent_device(hv_cpu->clk_evt, cpu);
> -
>  		hv_cpu->synic_message_page =
>  			(void *)get_zeroed_page(GFP_ATOMIC);
>  		if (hv_cpu->synic_message_page == NULL) {
> @@ -242,11 +133,6 @@ int hv_synic_alloc(void)
>  		INIT_LIST_HEAD(&hv_cpu->chan_list);
>  	}
>  
> -	if (direct_mode_enabled &&
> -	    hv_setup_stimer0_irq(&stimer0_irq, &stimer0_vector,
> -				hv_stimer0_isr))
> -		goto err;
> -
>  	return 0;
>  err:
>  	/*
> @@ -265,7 +151,6 @@ void hv_synic_free(void)
>  		struct hv_per_cpu_context *hv_cpu
>  			= per_cpu_ptr(hv_context.cpu_context, cpu);
>  
> -		kfree(hv_cpu->clk_evt);
>  		free_page((unsigned long)hv_cpu->synic_event_page);
>  		free_page((unsigned long)hv_cpu->synic_message_page);
>  		free_page((unsigned long)hv_cpu->post_msg_page);
> @@ -324,39 +209,10 @@ int hv_synic_init(unsigned int cpu)
>  
>  	hv_set_synic_state(sctrl.as_uint64);
>  
> -	/*
> -	 * Register the per-cpu clockevent source.
> -	 */
> -	if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE)
> -		clockevents_config_and_register(hv_cpu->clk_evt,
> -						HV_TIMER_FREQUENCY,
> -						HV_MIN_DELTA_TICKS,
> -						HV_MAX_MAX_DELTA_TICKS);
>  	return 0;
>  }
>  
>  /*
> - * hv_synic_clockevents_cleanup - Cleanup clockevent devices
> - */
> -void hv_synic_clockevents_cleanup(void)
> -{
> -	int cpu;
> -
> -	if (!(ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE))
> -		return;
> -
> -	if (direct_mode_enabled)
> -		hv_remove_stimer0_irq(stimer0_irq);
> -
> -	for_each_present_cpu(cpu) {
> -		struct hv_per_cpu_context *hv_cpu
> -			= per_cpu_ptr(hv_context.cpu_context, cpu);
> -
> -		clockevents_unbind_device(hv_cpu->clk_evt, cpu);
> -	}
> -}
> -
> -/*
>   * hv_synic_cleanup - Cleanup routine for hv_synic_init().
>   */
>  int hv_synic_cleanup(unsigned int cpu)
> @@ -401,16 +257,6 @@ int hv_synic_cleanup(unsigned int cpu)
>  	if (channel_found && vmbus_connection.conn_state == CONNECTED)
>  		return -EBUSY;
>  
> -	/* Turn off clockevent device */
> -	if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE) {
> -		struct hv_per_cpu_context *hv_cpu
> -			= this_cpu_ptr(hv_context.cpu_context);
> -
> -		clockevents_unbind_device(hv_cpu->clk_evt, cpu);
> -		hv_ce_shutdown(hv_cpu->clk_evt);
> -		put_cpu_ptr(hv_cpu);
> -	}
> -
>  	hv_get_synint_state(VMBUS_MESSAGE_SINT, shared_sint.as_uint64);
>  
>  	shared_sint.masked = 1;
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index cb86b133..ffd4ad8 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -151,7 +151,6 @@ struct hv_per_cpu_context {
>  	 * per-cpu list of the channels based on their CPU affinity.
>  	 */
>  	struct list_head chan_list;
> -	struct clock_event_device *clk_evt;
>  };
>  
>  struct hv_context {
> @@ -189,8 +188,6 @@ extern int hv_post_message(union hv_connection_id connection_id,
>  
>  extern int hv_synic_cleanup(unsigned int cpu);
>  
> -extern void hv_synic_clockevents_cleanup(void);
> -
>  /* Interface */
>  
>  
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 000b53e..8e442c5 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -43,6 +43,7 @@
>  #include <linux/kdebug.h>
>  #include <linux/efi.h>
>  #include <linux/random.h>
> +#include <clocksource/hyperv_syntimer.h>
>  #include "hyperv_vmbus.h"
>  
>  struct vmbus_dynid {
> @@ -939,17 +940,6 @@ static void vmbus_onmessage_work(struct work_struct *work)
>  	kfree(ctx);
>  }
>  
> -static void hv_process_timer_expiration(struct hv_message *msg,
> -					struct hv_per_cpu_context *hv_cpu)
> -{
> -	struct clock_event_device *dev = hv_cpu->clk_evt;
> -
> -	if (dev->event_handler)
> -		dev->event_handler(dev);
> -
> -	vmbus_signal_eom(msg, HVMSG_TIMER_EXPIRED);
> -}
> -
>  void vmbus_on_msg_dpc(unsigned long data)
>  {
>  	struct hv_per_cpu_context *hv_cpu = (void *)data;
> @@ -1143,9 +1133,10 @@ static void vmbus_isr(void)
>  
>  	/* Check if there are actual msgs to be processed */
>  	if (msg->header.message_type != HVMSG_NONE) {
> -		if (msg->header.message_type == HVMSG_TIMER_EXPIRED)
> -			hv_process_timer_expiration(msg, hv_cpu);
> -		else
> +		if (msg->header.message_type == HVMSG_TIMER_EXPIRED) {
> +			hv_stimer0_isr();
> +			vmbus_signal_eom(msg, HVMSG_TIMER_EXPIRED);
> +		} else
>  			tasklet_schedule(&hv_cpu->msg_dpc);
>  	}
>  
> @@ -1248,8 +1239,8 @@ static int vmbus_bus_init(void)
>  	if (ret)
>  		goto err_alloc;
>  	/*
> -	 * Initialize the per-cpu interrupt state and
> -	 * connect to the host.
> +	 * Initialize the per-cpu interrupt state and syntimer state.
> +	 * Then connect to the host.
>  	 */
>  	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "hyperv/vmbus:online",
>  				hv_synic_init, hv_synic_cleanup);
> @@ -1257,6 +1248,10 @@ static int vmbus_bus_init(void)
>  		goto err_alloc;
>  	hyperv_cpuhp_online = ret;
>  
> +	ret = hv_syntimer_alloc(VMBUS_MESSAGE_SINT);
> +	if (ret < 0)
> +		goto err_syntimer_alloc;
> +
>  	ret = vmbus_connect();
>  	if (ret)
>  		goto err_connect;
> @@ -1301,6 +1296,8 @@ static int vmbus_bus_init(void)
>  	return 0;
>  
>  err_connect:
> +	hv_syntimer_free();
> +err_syntimer_alloc:
>  	cpuhp_remove_state(hyperv_cpuhp_online);
>  err_alloc:
>  	hv_synic_free();
> @@ -1971,7 +1968,7 @@ static int vmbus_acpi_add(struct acpi_device *device)
>  
>  static void hv_kexec_handler(void)
>  {
> -	hv_synic_clockevents_cleanup();
> +	hv_syntimer_global_cleanup();
>  	vmbus_initiate_unload(false);
>  	vmbus_connection.conn_state = DISCONNECTED;
>  	/* Make sure conn_state is set as hv_synic_cleanup checks for it */
> @@ -1982,6 +1979,8 @@ static void hv_kexec_handler(void)
>  
>  static void hv_crash_handler(struct pt_regs *regs)
>  {
> +	int cpu;
> +
>  	vmbus_initiate_unload(true);
>  	/*
>  	 * In crash handler we can't schedule synic cleanup for all CPUs,
> @@ -1989,7 +1988,9 @@ static void hv_crash_handler(struct pt_regs *regs)
>  	 * for kdump.
>  	 */
>  	vmbus_connection.conn_state = DISCONNECTED;
> -	hv_synic_cleanup(smp_processor_id());
> +	cpu = smp_processor_id();
> +	hv_syntimer_cleanup(cpu);
> +	hv_synic_cleanup(cpu);
>  	hyperv_cleanup();
>  };
>  
> @@ -2038,7 +2039,7 @@ static void __exit vmbus_exit(void)
>  	hv_remove_kexec_handler();
>  	hv_remove_crash_handler();
>  	vmbus_connection.conn_state = DISCONNECTED;
> -	hv_synic_clockevents_cleanup();
> +	hv_syntimer_global_cleanup();
>  	vmbus_disconnect();
>  	hv_remove_vmbus_irq();
>  	for_each_online_cpu(cpu) {
> diff --git a/include/clocksource/hyperv_syntimer.h b/include/clocksource/hyperv_syntimer.h
> new file mode 100644
> index 0000000..154138b
> --- /dev/null
> +++ b/include/clocksource/hyperv_syntimer.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Definitions for the clocksource provided by the Hyper-V
> + * hypervisor to guest VMs, as described in the Hyper-V Top
> + * Level Functional Spec (TLFS).
> + *
> + * Copyright (C) 2019, Microsoft, Inc.
> + *
> + * Author:  Michael Kelley <mikelley@microsoft.com>
> + */
> +
> +#ifndef __CLKSOURCE_HYPERV_SYNTIMER_H
> +#define __CLKSOURCE_HYPERV_SYNTIMER_H
> +
> +#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
> +#define HV_MIN_DELTA_TICKS 1
> +
> +/* Routines called by the VMbus driver */
> +extern int hv_syntimer_alloc(int sint);
> +extern void hv_syntimer_free(void);
> +extern int hv_syntimer_cleanup(unsigned int cpu);
> +extern void hv_syntimer_global_cleanup(void);
> +extern void hv_stimer0_isr(void);
> +
> +#endif

-- 
Vitaly