hw/i386/kvm/clock.c - qemu - Git at Google

 /*
  * QEMU KVM support, paravirtual clock device
  *
  * Copyright (C) 2011 Siemens AG
  *
  * Authors:
  *  Jan Kiszka        <jan.kiszka@siemens.com>
  *
  * This work is licensed under the terms of the GNU GPL version 2.
  * See the COPYING file in the top-level directory.
  *
  * Contributions after 2012-01-13 are licensed under the terms of the
  * GNU GPL, version 2 or (at your option) any later version.
  */

 #include "qemu/osdep.h"
 #include "qemu/host-utils.h"
 #include "qemu/module.h"
 #include "sysemu/kvm.h"
 #include "sysemu/runstate.h"
 #include "sysemu/hw_accel.h"
 #include "kvm/kvm_i386.h"
 #include "migration/vmstate.h"
 #include "hw/sysbus.h"
 #include "hw/i386/kvm/clock.h"
 #include "hw/qdev-properties.h"
 #include "qapi/error.h"

 #include <linux/kvm.h>
 #include "standard-headers/asm-x86/kvm_para.h"
 #include "qom/object.h"

 #define TYPE_KVM_CLOCK "kvmclock"
 OBJECT_DECLARE_SIMPLE_TYPE(KVMClockState, KVM_CLOCK)

 struct KVMClockState {
     /*< private >*/
     SysBusDevice busdev;
     /*< public >*/

     uint64_t clock;
     bool clock_valid;

     /* whether the 'clock' value was obtained in the 'paused' state */
     bool runstate_paused;

     /* whether machine type supports reliable KVM_GET_CLOCK */
     bool mach_use_reliable_get_clock;

     /* whether the 'clock' value was obtained in a host with
      * reliable KVM_GET_CLOCK */
     bool clock_is_reliable;
 };

 struct pvclock_vcpu_time_info {
     uint32_t   version;
     uint32_t   pad0;
     uint64_t   tsc_timestamp;
     uint64_t   system_time;
     uint32_t   tsc_to_system_mul;
     int8_t     tsc_shift;
     uint8_t    flags;
     uint8_t    pad[2];
 } __attribute__((__packed__)); /* 32 bytes */

 static uint64_t kvmclock_current_nsec(KVMClockState *s)
 {
     CPUState *cpu = first_cpu;
     CPUX86State *env = cpu_env(cpu);
     hwaddr kvmclock_struct_pa;
     uint64_t migration_tsc = env->tsc;
     struct pvclock_vcpu_time_info time;
     uint64_t delta;
     uint64_t nsec_lo;
     uint64_t nsec_hi;
     uint64_t nsec;

     cpu_synchronize_state(cpu);

     if (!(env->system_time_msr & 1ULL)) {
         /* KVM clock not active */
         return 0;
     }

     kvmclock_struct_pa = env->system_time_msr & ~1ULL;
     cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));

     assert(time.tsc_timestamp <= migration_tsc);
     delta = migration_tsc - time.tsc_timestamp;
     if (time.tsc_shift < 0) {
         delta >>= -time.tsc_shift;
     } else {
         delta <<= time.tsc_shift;
     }

     mulu64(&nsec_lo, &nsec_hi, delta, time.tsc_to_system_mul);
     nsec = (nsec_lo >> 32) | (nsec_hi << 32);
     return nsec + time.system_time;
 }

 static void kvm_update_clock(KVMClockState *s)
 {
     struct kvm_clock_data data;
     int ret;

     ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
     if (ret < 0) {
         fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(-ret));
                 abort();
     }
     s->clock = data.clock;

     /* If kvm_has_adjust_clock_stable() is false, KVM_GET_CLOCK returns
      * essentially CLOCK_MONOTONIC plus a guest-specific adjustment.  This
      * can drift from the TSC-based value that is computed by the guest,
      * so we need to go through kvmclock_current_nsec().  If
      * kvm_has_adjust_clock_stable() is true, and the flags contain
      * KVM_CLOCK_TSC_STABLE, then KVM_GET_CLOCK returns a TSC-based value
      * and kvmclock_current_nsec() is not necessary.
      *
      * Here, however, we need not check KVM_CLOCK_TSC_STABLE.  This is because:
      *
      * - if the host has disabled the kvmclock master clock, the guest already
      *   has protection against time going backwards.  This "safety net" is only
      *   absent when kvmclock is stable;
      *
      * - therefore, we can replace a check like
      *
      *       if last KVM_GET_CLOCK was not reliable then
      *               read from memory
      *
      *   with
      *
      *       if last KVM_GET_CLOCK was not reliable && masterclock is enabled
      *               read from memory
      *
      * However:
      *
      * - if kvm_has_adjust_clock_stable() returns false, the left side is
      *   always true (KVM_GET_CLOCK is never reliable), and the right side is
      *   unknown (because we don't have data.flags).  We must assume it's true
      *   and read from memory.
      *
      * - if kvm_has_adjust_clock_stable() returns true, the result of the &&
      *   is always false (masterclock is enabled iff KVM_GET_CLOCK is reliable)
      *
      * So we can just use this instead:
      *
      *       if !kvm_has_adjust_clock_stable() then
      *               read from memory
      */
     s->clock_is_reliable = kvm_has_adjust_clock_stable();
 }

 static void do_kvmclock_ctrl(CPUState *cpu, run_on_cpu_data data)
 {
     int ret = kvm_vcpu_ioctl(cpu, KVM_KVMCLOCK_CTRL, 0);

     if (ret && ret != -EINVAL) {
         fprintf(stderr, "%s: %s\n", __func__, strerror(-ret));
     }
 }

 static void kvmclock_vm_state_change(void *opaque, bool running,
                                      RunState state)
 {
     KVMClockState *s = opaque;
     CPUState *cpu;
     int cap_clock_ctrl = kvm_check_extension(kvm_state, KVM_CAP_KVMCLOCK_CTRL);
     int ret;

     if (running) {
         struct kvm_clock_data data = {};

         /*
          * If the host where s->clock was read did not support reliable
          * KVM_GET_CLOCK, read kvmclock value from memory.
          */
         if (!s->clock_is_reliable) {
             uint64_t pvclock_via_mem = kvmclock_current_nsec(s);
             /* We can't rely on the saved clock value, just discard it */
             if (pvclock_via_mem) {
                 s->clock = pvclock_via_mem;
             }
         }

         s->clock_valid = false;

         data.clock = s->clock;
         ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
         if (ret < 0) {
             fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(-ret));
             abort();
         }

         if (!cap_clock_ctrl) {
             return;
         }
         CPU_FOREACH(cpu) {
             run_on_cpu(cpu, do_kvmclock_ctrl, RUN_ON_CPU_NULL);
         }
     } else {

         if (s->clock_valid) {
             return;
         }

         s->runstate_paused = runstate_check(RUN_STATE_PAUSED);

         kvm_synchronize_all_tsc();

         kvm_update_clock(s);
         /*
          * If the VM is stopped, declare the clock state valid to
          * avoid re-reading it on next vmsave (which would return
          * a different value). Will be reset when the VM is continued.
          */
         s->clock_valid = true;
     }
 }

 static void kvmclock_realize(DeviceState *dev, Error **errp)
 {
     KVMClockState *s = KVM_CLOCK(dev);

     if (!kvm_enabled()) {
         error_setg(errp, "kvmclock device requires KVM");
         return;
     }

     kvm_update_clock(s);

     qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
 }

 static bool kvmclock_clock_is_reliable_needed(void *opaque)
 {
     KVMClockState *s = opaque;

     return s->mach_use_reliable_get_clock;
 }

 static const VMStateDescription kvmclock_reliable_get_clock = {
     .name = "kvmclock/clock_is_reliable",
     .version_id = 1,
     .minimum_version_id = 1,
     .needed = kvmclock_clock_is_reliable_needed,
     .fields = (VMStateField[]) {
         VMSTATE_BOOL(clock_is_reliable, KVMClockState),
         VMSTATE_END_OF_LIST()
     }
 };

 /*
  * When migrating, assume the source has an unreliable
  * KVM_GET_CLOCK unless told otherwise.
  */
 static int kvmclock_pre_load(void *opaque)
 {
     KVMClockState *s = opaque;

     s->clock_is_reliable = false;

     return 0;
 }

 /*
  * When migrating a running guest, read the clock just
  * before migration, so that the guest clock counts
  * during the events between:
  *
  *  * vm_stop()
  *  *
  *  * pre_save()
  *
  *  This reduces kvmclock difference on migration from 5s
  *  to 0.1s (when max_downtime == 5s), because sending the
  *  final pages of memory (which happens between vm_stop()
  *  and pre_save()) takes max_downtime.
  */
 static int kvmclock_pre_save(void *opaque)
 {
     KVMClockState *s = opaque;

     if (!s->runstate_paused) {
         kvm_update_clock(s);
     }

     return 0;
 }

 static const VMStateDescription kvmclock_vmsd = {
     .name = "kvmclock",
     .version_id = 1,
     .minimum_version_id = 1,
     .pre_load = kvmclock_pre_load,
     .pre_save = kvmclock_pre_save,
     .fields = (VMStateField[]) {
         VMSTATE_UINT64(clock, KVMClockState),
         VMSTATE_END_OF_LIST()
     },
     .subsections = (const VMStateDescription * []) {
         &kvmclock_reliable_get_clock,
         NULL
     }
 };

 static Property kvmclock_properties[] = {
     DEFINE_PROP_BOOL("x-mach-use-reliable-get-clock", KVMClockState,
                       mach_use_reliable_get_clock, true),
     DEFINE_PROP_END_OF_LIST(),
 };

 static void kvmclock_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);

     dc->realize = kvmclock_realize;
     dc->vmsd = &kvmclock_vmsd;
     device_class_set_props(dc, kvmclock_properties);
 }

 static const TypeInfo kvmclock_info = {
     .name          = TYPE_KVM_CLOCK,
     .parent        = TYPE_SYS_BUS_DEVICE,
     .instance_size = sizeof(KVMClockState),
     .class_init    = kvmclock_class_init,
 };

 /* Note: Must be called after VCPU initialization. */
 void kvmclock_create(bool create_always)
 {
     X86CPU *cpu = X86_CPU(first_cpu);

     assert(kvm_enabled());
     if (create_always ||
         cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) |
                                        (1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
         sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);
     }
 }

 static void kvmclock_register_types(void)
 {
     type_register_static(&kvmclock_info);
 }

 type_init(kvmclock_register_types)
	/*
	* QEMU KVM support, paravirtual clock device
	*
	* Copyright (C) 2011 Siemens AG
	*
	* Authors:
	* Jan Kiszka <jan.kiszka@siemens.com>
	*
	* This work is licensed under the terms of the GNU GPL version 2.
	* See the COPYING file in the top-level directory.
	*
	* Contributions after 2012-01-13 are licensed under the terms of the
	* GNU GPL, version 2 or (at your option) any later version.
	*/

	#include "qemu/osdep.h"
	#include "qemu/host-utils.h"
	#include "qemu/module.h"
	#include "sysemu/kvm.h"
	#include "sysemu/runstate.h"
	#include "sysemu/hw_accel.h"
	#include "kvm/kvm_i386.h"
	#include "migration/vmstate.h"
	#include "hw/sysbus.h"
	#include "hw/i386/kvm/clock.h"
	#include "hw/qdev-properties.h"
	#include "qapi/error.h"

	#include <linux/kvm.h>
	#include "standard-headers/asm-x86/kvm_para.h"
	#include "qom/object.h"

	#define TYPE_KVM_CLOCK "kvmclock"
	OBJECT_DECLARE_SIMPLE_TYPE(KVMClockState, KVM_CLOCK)

	struct KVMClockState {
	/< private >/
	SysBusDevice busdev;
	/< public >/

	uint64_t clock;
	bool clock_valid;

	/* whether the 'clock' value was obtained in the 'paused' state */
	bool runstate_paused;

	/* whether machine type supports reliable KVM_GET_CLOCK */
	bool mach_use_reliable_get_clock;

	/* whether the 'clock' value was obtained in a host with
	* reliable KVM_GET_CLOCK */
	bool clock_is_reliable;
	};

	struct pvclock_vcpu_time_info {
	uint32_t version;
	uint32_t pad0;
	uint64_t tsc_timestamp;
	uint64_t system_time;
	uint32_t tsc_to_system_mul;
	int8_t tsc_shift;
	uint8_t flags;
	uint8_t pad[2];
	} __attribute__((__packed__)); /* 32 bytes */

	static uint64_t kvmclock_current_nsec(KVMClockState *s)
	{
	CPUState *cpu = first_cpu;
	CPUX86State *env = cpu_env(cpu);
	hwaddr kvmclock_struct_pa;
	uint64_t migration_tsc = env->tsc;
	struct pvclock_vcpu_time_info time;
	uint64_t delta;
	uint64_t nsec_lo;
	uint64_t nsec_hi;
	uint64_t nsec;

	cpu_synchronize_state(cpu);

	if (!(env->system_time_msr & 1ULL)) {
	/* KVM clock not active */
	return 0;
	}

	kvmclock_struct_pa = env->system_time_msr & ~1ULL;
	cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));

	assert(time.tsc_timestamp <= migration_tsc);
	delta = migration_tsc - time.tsc_timestamp;
	if (time.tsc_shift < 0) {
	delta >>= -time.tsc_shift;
	} else {
	delta <<= time.tsc_shift;
	}

	mulu64(&nsec_lo, &nsec_hi, delta, time.tsc_to_system_mul);
	nsec = (nsec_lo >> 32) \| (nsec_hi << 32);
	return nsec + time.system_time;
	}

	static void kvm_update_clock(KVMClockState *s)
	{
	struct kvm_clock_data data;
	int ret;

	ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
	if (ret < 0) {
	fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(-ret));
	abort();
	}
	s->clock = data.clock;

	/* If kvm_has_adjust_clock_stable() is false, KVM_GET_CLOCK returns
	* essentially CLOCK_MONOTONIC plus a guest-specific adjustment. This
	* can drift from the TSC-based value that is computed by the guest,
	* so we need to go through kvmclock_current_nsec(). If
	* kvm_has_adjust_clock_stable() is true, and the flags contain
	* KVM_CLOCK_TSC_STABLE, then KVM_GET_CLOCK returns a TSC-based value
	* and kvmclock_current_nsec() is not necessary.
	*
	* Here, however, we need not check KVM_CLOCK_TSC_STABLE. This is because:
	*
	* - if the host has disabled the kvmclock master clock, the guest already
	* has protection against time going backwards. This "safety net" is only
	* absent when kvmclock is stable;
	*
	* - therefore, we can replace a check like
	*
	* if last KVM_GET_CLOCK was not reliable then
	* read from memory
	*
	* with
	*
	* if last KVM_GET_CLOCK was not reliable && masterclock is enabled
	* read from memory
	*
	* However:
	*
	* - if kvm_has_adjust_clock_stable() returns false, the left side is
	* always true (KVM_GET_CLOCK is never reliable), and the right side is
	* unknown (because we don't have data.flags). We must assume it's true
	* and read from memory.
	*
	* - if kvm_has_adjust_clock_stable() returns true, the result of the &&
	* is always false (masterclock is enabled iff KVM_GET_CLOCK is reliable)
	*
	* So we can just use this instead:
	*
	* if !kvm_has_adjust_clock_stable() then
	* read from memory
	*/
	s->clock_is_reliable = kvm_has_adjust_clock_stable();
	}

	static void do_kvmclock_ctrl(CPUState *cpu, run_on_cpu_data data)
	{
	int ret = kvm_vcpu_ioctl(cpu, KVM_KVMCLOCK_CTRL, 0);

	if (ret && ret != -EINVAL) {
	fprintf(stderr, "%s: %s\n", __func__, strerror(-ret));
	}
	}

	static void kvmclock_vm_state_change(void *opaque, bool running,
	RunState state)
	{
	KVMClockState *s = opaque;
	CPUState *cpu;
	int cap_clock_ctrl = kvm_check_extension(kvm_state, KVM_CAP_KVMCLOCK_CTRL);
	int ret;

	if (running) {
	struct kvm_clock_data data = {};

	/*
	* If the host where s->clock was read did not support reliable
	* KVM_GET_CLOCK, read kvmclock value from memory.
	*/
	if (!s->clock_is_reliable) {
	uint64_t pvclock_via_mem = kvmclock_current_nsec(s);
	/* We can't rely on the saved clock value, just discard it */
	if (pvclock_via_mem) {
	s->clock = pvclock_via_mem;
	}
	}

	s->clock_valid = false;

	data.clock = s->clock;
	ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
	if (ret < 0) {
	fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(-ret));
	abort();
	}

	if (!cap_clock_ctrl) {
	return;
	}
	CPU_FOREACH(cpu) {
	run_on_cpu(cpu, do_kvmclock_ctrl, RUN_ON_CPU_NULL);
	}
	} else {

	if (s->clock_valid) {
	return;
	}

	s->runstate_paused = runstate_check(RUN_STATE_PAUSED);

	kvm_synchronize_all_tsc();

	kvm_update_clock(s);
	/*
	* If the VM is stopped, declare the clock state valid to
	* avoid re-reading it on next vmsave (which would return
	* a different value). Will be reset when the VM is continued.
	*/
	s->clock_valid = true;
	}
	}

	static void kvmclock_realize(DeviceState dev, Error *errp)
	{
	KVMClockState *s = KVM_CLOCK(dev);

	if (!kvm_enabled()) {
	error_setg(errp, "kvmclock device requires KVM");
	return;
	}

	kvm_update_clock(s);

	qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
	}

	static bool kvmclock_clock_is_reliable_needed(void *opaque)
	{
	KVMClockState *s = opaque;

	return s->mach_use_reliable_get_clock;
	}

	static const VMStateDescription kvmclock_reliable_get_clock = {
	.name = "kvmclock/clock_is_reliable",
	.version_id = 1,
	.minimum_version_id = 1,
	.needed = kvmclock_clock_is_reliable_needed,
	.fields = (VMStateField[]) {
	VMSTATE_BOOL(clock_is_reliable, KVMClockState),
	VMSTATE_END_OF_LIST()
	}
	};

	/*
	* When migrating, assume the source has an unreliable
	* KVM_GET_CLOCK unless told otherwise.
	*/
	static int kvmclock_pre_load(void *opaque)
	{
	KVMClockState *s = opaque;

	s->clock_is_reliable = false;

	return 0;
	}

	/*
	* When migrating a running guest, read the clock just
	* before migration, so that the guest clock counts
	* during the events between:
	*
	* * vm_stop()
	* *
	* * pre_save()
	*
	* This reduces kvmclock difference on migration from 5s
	* to 0.1s (when max_downtime == 5s), because sending the
	* final pages of memory (which happens between vm_stop()
	* and pre_save()) takes max_downtime.
	*/
	static int kvmclock_pre_save(void *opaque)
	{
	KVMClockState *s = opaque;

	if (!s->runstate_paused) {
	kvm_update_clock(s);
	}

	return 0;
	}

	static const VMStateDescription kvmclock_vmsd = {
	.name = "kvmclock",
	.version_id = 1,
	.minimum_version_id = 1,
	.pre_load = kvmclock_pre_load,
	.pre_save = kvmclock_pre_save,
	.fields = (VMStateField[]) {
	VMSTATE_UINT64(clock, KVMClockState),
	VMSTATE_END_OF_LIST()
	},
	.subsections = (const VMStateDescription * []) {
	&kvmclock_reliable_get_clock,
	NULL
	}
	};

	static Property kvmclock_properties[] = {
	DEFINE_PROP_BOOL("x-mach-use-reliable-get-clock", KVMClockState,
	mach_use_reliable_get_clock, true),
	DEFINE_PROP_END_OF_LIST(),
	};

	static void kvmclock_class_init(ObjectClass klass, void data)
	{
	DeviceClass *dc = DEVICE_CLASS(klass);

	dc->realize = kvmclock_realize;
	dc->vmsd = &kvmclock_vmsd;
	device_class_set_props(dc, kvmclock_properties);
	}

	static const TypeInfo kvmclock_info = {
	.name = TYPE_KVM_CLOCK,
	.parent = TYPE_SYS_BUS_DEVICE,
	.instance_size = sizeof(KVMClockState),
	.class_init = kvmclock_class_init,
	};

	/* Note: Must be called after VCPU initialization. */
	void kvmclock_create(bool create_always)
	{
	X86CPU *cpu = X86_CPU(first_cpu);

	assert(kvm_enabled());
	if (create_always \|\|
	cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) \|
	(1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
	sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);
	}
	}

	static void kvmclock_register_types(void)
	{
	type_register_static(&kvmclock_info);
	}

	type_init(kvmclock_register_types)