clocksource/drivers: Make Hyper-V clocksource ISA agnostic

Hyper-V clock/timer code and data structures are currently mixed
in with other code in the ISA independent drivers/hv directory as
well as the ISA dependent Hyper-V code under arch/x86.

Consolidate this code and data structures into a Hyper-V clocksource driver
to better follow the Linux model. In doing so, separate out the ISA
dependent portions so the new clocksource driver works for x86 and for the
in-process Hyper-V on ARM64 code.

To start, move the existing clockevents code to create the new clocksource
driver. Update the VMbus driver to call initialization and cleanup routines
since the Hyper-V synthetic timers are not independently enumerated in
ACPI.

No behavior is changed and no new functionality is added.

Suggested-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: "bp@alien8.de" <bp@alien8.de>
Cc: "will.deacon@arm.com" <will.deacon@arm.com>
Cc: "catalin.marinas@arm.com" <catalin.marinas@arm.com>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>
Cc: "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>
Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Cc: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
Cc: "olaf@aepfle.de" <olaf@aepfle.de>
Cc: "apw@canonical.com" <apw@canonical.com>
Cc: "jasowang@redhat.com" <jasowang@redhat.com>
Cc: "marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>
Cc: Sunil Muthuswamy <sunilmut@microsoft.com>
Cc: KY Srinivasan <kys@microsoft.com>
Cc: "sashal@kernel.org" <sashal@kernel.org>
Cc: "vincenzo.frascino@arm.com" <vincenzo.frascino@arm.com>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Cc: "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>
Cc: "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>
Cc: "arnd@arndb.de" <arnd@arndb.de>
Cc: "linux@armlinux.org.uk" <linux@armlinux.org.uk>
Cc: "ralf@linux-mips.org" <ralf@linux-mips.org>
Cc: "paul.burton@mips.com" <paul.burton@mips.com>
Cc: "daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>
Cc: "salyzyn@android.com" <salyzyn@android.com>
Cc: "pcc@google.com" <pcc@google.com>
Cc: "shuah@kernel.org" <shuah@kernel.org>
Cc: "0x7f454c46@gmail.com" <0x7f454c46@gmail.com>
Cc: "linux@rasmusvillemoes.dk" <linux@rasmusvillemoes.dk>
Cc: "huw@codeweavers.com" <huw@codeweavers.com>
Cc: "sfr@canb.auug.org.au" <sfr@canb.auug.org.au>
Cc: "pbonzini@redhat.com" <pbonzini@redhat.com>
Cc: "rkrcmar@redhat.com" <rkrcmar@redhat.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>
Link: https://lkml.kernel.org/r/1561955054-1838-2-git-send-email-mikelley@microsoft.com

10 files changed, 268 insertions, 176 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index a2812972b7b0..bfde42a76a95 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7313,6 +7313,7 @@ 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_timer.c
 F:      drivers/hid/hid-hyperv.c
 F:      drivers/hv/
 F:      drivers/input/serio/hyperv-keyboard.c
@@ -7323,6 +7324,7 @@ F:	drivers/uio/uio_hv_generic.c
 F:      drivers/video/fbdev/hyperv_fb.c
 F:      drivers/iommu/hyperv_iommu.c
 F:      net/vmw_vsock/hyperv_transport.c
+F:      include/clocksource/hyperv_timer.h
 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 cdf44aa9a501..af78cd72b8f3 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 7df29f08871b..1e5f7a03ddf5 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -17,6 +17,7 @@
 #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>
@@ -80,6 +81,7 @@ __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();
@@ -89,7 +91,7 @@ __visible void __irq_entry hv_stimer0_vector_handler(struct pt_regs *regs)
 int hv_setup_stimer0_irq(int *irq, int *vector, void (*handler)(void))
 {
         *vector = HYPERV_STIMER0_VECTOR;
-        *irq = 0;   /* Unused on x86/x64 */
+        *irq = -1;   /* Unused on x86/x64 */
         hv_stimer0_handler = handler;
         return 0;
 }
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 5582252efb31..2e7936e7833f 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -86,3 +86,4 @@ 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_TIMER)              += hyperv_timer.o
diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
new file mode 100644
index 000000000000..68a28af31561
--- /dev/null
+++ b/drivers/clocksource/hyperv_timer.c
@@ -0,0 +1,200 @@
+// 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/mm.h>
+#include <clocksource/hyperv_timer.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;
+
+/*
+ * 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;
+
+        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_stimer_init - Per-cpu initialization of the clockevent
+ */
+void hv_stimer_init(unsigned int cpu)
+{
+        struct clock_event_device *ce;
+
+        /*
+         * Synthetic timers are always available except on old versions of
+         * Hyper-V on x86.  In that case, just return as Linux will use a
+         * clocksource based on emulated PIT or LAPIC timer hardware.
+         */
+        if (!(ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE))
+                return;
+
+        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);
+}
+EXPORT_SYMBOL_GPL(hv_stimer_init);
+
+/*
+ * hv_stimer_cleanup - Per-cpu cleanup of the clockevent
+ */
+void hv_stimer_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);
+                hv_ce_shutdown(ce);
+        }
+}
+EXPORT_SYMBOL_GPL(hv_stimer_cleanup);
+
+/* hv_stimer_alloc - Global initialization of the clockevent and stimer0 */
+int hv_stimer_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) {
+                ret = hv_setup_stimer0_irq(&stimer0_irq, &stimer0_vector,
+                                hv_stimer0_isr);
+                if (ret) {
+                        free_percpu(hv_clock_event);
+                        hv_clock_event = NULL;
+                        return ret;
+                }
+        }
+
+        stimer0_message_sint = sint;
+        return 0;
+}
+EXPORT_SYMBOL_GPL(hv_stimer_alloc);
+
+/* hv_stimer_free - Free global resources allocated by hv_stimer_alloc() */
+void hv_stimer_free(void)
+{
+        if (direct_mode_enabled && (stimer0_irq != 0)) {
+                hv_remove_stimer0_irq(stimer0_irq);
+                stimer0_irq = 0;
+        }
+        free_percpu(hv_clock_event);
+        hv_clock_event = NULL;
+}
+EXPORT_SYMBOL_GPL(hv_stimer_free);
+
+/*
+ * Do a global cleanup of clockevents for the cases of kexec and
+ * vmbus exit
+ */
+void hv_stimer_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_stimer_free();
+}
+EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 1c1a2514d6f3..c423e57ae888 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -10,6 +10,9 @@ config HYPERV
           Select this option to run Linux as a Hyper-V client operating
           system.
 
+config HYPERV_TIMER
+        def_bool HYPERV
+
 config HYPERV_TSCPAGE
        def_bool HYPERV && X86_64
 
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index a1ea482183e8..6188fb7dda42 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -16,6 +16,7 @@
 #include <linux/version.h>
 #include <linux/random.h>
 #include <linux/clockchips.h>
+#include <clocksource/hyperv_timer.h>
 #include <asm/mshyperv.h>
 #include "hyperv_vmbus.h"
 
@@ -23,21 +24,6 @@
 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
@@ -47,9 +33,6 @@ 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;
 }
 
@@ -88,89 +71,6 @@ 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;
@@ -199,14 +99,6 @@ 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) {
@@ -229,11 +121,6 @@ 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:
         /*
@@ -252,7 +139,6 @@ 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);
@@ -311,36 +197,9 @@ 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;
+        hv_stimer_init(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);
-        }
+        return 0;
 }
 
 /*
@@ -388,14 +247,7 @@ 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);
-        }
+        hv_stimer_cleanup(cpu);
 
         hv_get_synint_state(VMBUS_MESSAGE_SINT, shared_sint.as_uint64);
 
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index b8e1ff05f110..362e70e9d145 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -138,7 +138,6 @@ 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 {
@@ -176,8 +175,6 @@ extern int hv_synic_init(unsigned int cpu);
 
 extern int hv_synic_cleanup(unsigned int cpu);
 
-extern void hv_synic_clockevents_cleanup(void);
-
 /* Interface */
 
 void hv_ringbuffer_pre_init(struct vmbus_channel *channel);
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 92b1874b3eb3..72d5a7cde7ea 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -30,6 +30,7 @@
 #include <linux/kdebug.h>
 #include <linux/efi.h>
 #include <linux/random.h>
+#include <clocksource/hyperv_timer.h>
 #include "hyperv_vmbus.h"
 
 struct vmbus_dynid {
@@ -955,17 +956,6 @@ 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;
@@ -1159,9 +1149,10 @@ 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);
         }
 
@@ -1263,14 +1254,19 @@ static int vmbus_bus_init(void)
         ret = hv_synic_alloc();
         if (ret)
                 goto err_alloc;
+
+        ret = hv_stimer_alloc(VMBUS_MESSAGE_SINT);
+        if (ret < 0)
+                goto err_alloc;
+
         /*
-         * Initialize the per-cpu interrupt state and
-         * connect to the host.
+         * Initialize the per-cpu interrupt state and stimer state.
+         * Then connect to the host.
          */
         ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "hyperv/vmbus:online",
                                 hv_synic_init, hv_synic_cleanup);
         if (ret < 0)
-                goto err_alloc;
+                goto err_cpuhp;
         hyperv_cpuhp_online = ret;
 
         ret = vmbus_connect();
@@ -1318,6 +1314,8 @@ static int vmbus_bus_init(void)
 
 err_connect:
         cpuhp_remove_state(hyperv_cpuhp_online);
+err_cpuhp:
+        hv_stimer_free();
 err_alloc:
         hv_synic_free();
         hv_remove_vmbus_irq();
@@ -2064,7 +2062,7 @@ static struct acpi_driver vmbus_acpi_driver = {
 
 static void hv_kexec_handler(void)
 {
-        hv_synic_clockevents_cleanup();
+        hv_stimer_global_cleanup();
         vmbus_initiate_unload(false);
         vmbus_connection.conn_state = DISCONNECTED;
         /* Make sure conn_state is set as hv_synic_cleanup checks for it */
@@ -2075,6 +2073,8 @@ 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,
@@ -2082,7 +2082,9 @@ 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_stimer_cleanup(cpu);
+        hv_synic_cleanup(cpu);
         hyperv_cleanup();
 };
 
@@ -2131,7 +2133,7 @@ static void __exit vmbus_exit(void)
         hv_remove_kexec_handler();
         hv_remove_crash_handler();
         vmbus_connection.conn_state = DISCONNECTED;
-        hv_synic_clockevents_cleanup();
+        hv_stimer_global_cleanup();
         vmbus_disconnect();
         hv_remove_vmbus_irq();
         for_each_online_cpu(cpu) {
diff --git a/include/clocksource/hyperv_timer.h b/include/clocksource/hyperv_timer.h
new file mode 100644
index 000000000000..0cd73f7bc992
--- /dev/null
+++ b/include/clocksource/hyperv_timer.h
@@ -0,0 +1,27 @@
+/* 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_TIMER_H
+#define __CLKSOURCE_HYPERV_TIMER_H
+
+#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
+#define HV_MIN_DELTA_TICKS 1
+
+/* Routines called by the VMbus driver */
+extern int hv_stimer_alloc(int sint);
+extern void hv_stimer_free(void);
+extern void hv_stimer_init(unsigned int cpu);
+extern void hv_stimer_cleanup(unsigned int cpu);
+extern void hv_stimer_global_cleanup(void);
+extern void hv_stimer0_isr(void);
+
+#endif