[RFC PATCH v3 4/5] kvm/x86: virtual suspend time injection: Implement host side

Hikaru Nishida
2021-10-20T12:05:26Z

Add main logics that adjust the guest's clocks and notify about the
suspension to the guest.

Adjustment flow:
- Before going into suspend, KVM_REQ_SUSPEND_TIME_ADJ will be
requested for each vcpus through the PM notifier if the suspend time
injection is enabled for the kvm.
- Before the first vmenter after the resume, each vcpu will check the
the request and do two kinds of adjustments.
- One is kvm-wide adjustment: kvm-clock will be adjusted to the value
before the suspend.
- Another is per-vcpu adjustment: tsc will be adjusted to the value
before the suspend.
- Those adjustments happen before the vcpu run: so the guest will not
observe the "rewinding" of the clocks.
- After the adjustment is made, the guest will be notified about the
adjustment through HYPERVISOR_CALLBACK_VECTOR IRQ.
- It is guest's responsibility to adjust their CLOCK_BOOTTIME and
the wall clock to reflect the suspend.
This will be done in the later patch.

Signed-off-by: Hikaru Nishida <hikalium@chromium.org>
---

Changes in v3:
- Used PM notifier instead of modifying timekeeping_resume()
- This avoids holding kvm_lock under interrupt disabled context.
- Used KVM_REQ_* to make a request for vcpus.
- Reused HYPERVISOR_CALLBACK_VECTOR IRQ instead of adding a new one.
- Extracted arch-independent parts.

arch/x86/include/asm/kvm_host.h | 2 +
arch/x86/kvm/Kconfig | 13 ++++
arch/x86/kvm/cpuid.c | 4 ++
arch/x86/kvm/x86.c | 109 ++++++++++++++++++++++++++++++++
include/linux/kvm_host.h | 48 ++++++++++++++
virt/kvm/kvm_main.c | 88 ++++++++++++++++++++++++++
6 files changed, 264 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f8f48a7ec577..bdff8f777632 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1085,6 +1085,8 @@ struct kvm_arch {
bool pause_in_guest;
bool cstate_in_guest;

+ u64 msr_suspend_time;
+
unsigned long irq_sources_bitmap;
s64 kvmclock_offset;
raw_spinlock_t tsc_write_lock;
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index ac69894eab88..6d68a4d6be87 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -129,4 +129,17 @@ config KVM_MMU_AUDIT
This option adds a R/W kVM module parameter 'mmu_audit', which allows
auditing of KVM MMU events at runtime.

+config KVM_VIRT_SUSPEND_TIMING
+ bool "Host support for virtual suspend time injection"
+ depends on KVM=y && HAVE_KVM_PM_NOTIFIER
+ default n
+ help
+ This option makes the host's suspension reflected on the guest's clocks.
+ In other words, guest's CLOCK_MONOTONIC will stop and
+ CLOCK_BOOTTIME keeps running during the host's suspension.
+ This feature will only be effective when both guest and host support
+ this feature. For the guest side, see KVM_VIRT_SUSPEND_TIMING_GUEST.
+
+ If unsure, say N.
+
endif # VIRTUALIZATION
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 751aa85a3001..34a2fe147503 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -886,6 +886,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
(1 << KVM_FEATURE_PV_SCHED_YIELD) |
(1 << KVM_FEATURE_ASYNC_PF_INT);

+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+ entry->eax |= (1 << KVM_FEATURE_HOST_SUSPEND_TIME);
+#endif
+
if (sched_info_on())
entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index aabd3a2ec1bc..b6d0d7f73196 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1367,6 +1367,7 @@ static const u32 emulated_msrs_all[] = {

MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
MSR_KVM_PV_EOI_EN, MSR_KVM_ASYNC_PF_INT, MSR_KVM_ASYNC_PF_ACK,
+ MSR_KVM_HOST_SUSPEND_TIME,

MSR_IA32_TSC_ADJUST,
MSR_IA32_TSC_DEADLINE,
@@ -3467,6 +3468,19 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
vcpu->arch.msr_kvm_poll_control = data;
break;

+ case MSR_KVM_HOST_SUSPEND_TIME:
+ if (!guest_pv_has(vcpu, KVM_FEATURE_HOST_SUSPEND_TIME))
+ return 1;
+
+ if (!(data & KVM_MSR_ENABLED))
+ break;
+
+ if (kvm_init_suspend_time_ghc(vcpu->kvm, data & ~1ULL))
+ return 1;
+
+ vcpu->kvm->arch.msr_suspend_time = data;
+ break;
+
case MSR_IA32_MCG_CTL:
case MSR_IA32_MCG_STATUS:
case MSR_IA32_MC0_CTL ... MSR_IA32_MCx_CTL(KVM_MAX_MCE_BANKS) - 1:
@@ -3785,6 +3799,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

msr_info->data = vcpu->arch.msr_kvm_poll_control;
break;
+ case MSR_KVM_HOST_SUSPEND_TIME:
+ if (!guest_pv_has(vcpu, KVM_FEATURE_HOST_SUSPEND_TIME))
+ return 1;
+
+ msr_info->data = vcpu->kvm->arch.msr_suspend_time;
+ break;
case MSR_IA32_P5_MC_ADDR:
case MSR_IA32_P5_MC_TYPE:
case MSR_IA32_MCG_CAP:
@@ -9392,6 +9412,93 @@ void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu)
}
EXPORT_SYMBOL_GPL(__kvm_request_immediate_exit);

+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+bool virt_suspend_time_enabled(struct kvm *kvm)
+{
+ return kvm->arch.msr_suspend_time & KVM_MSR_ENABLED;
+}
+
+/*
+ * Do per-vcpu suspend time adjustment (tsc) and
+ * make an interrupt to notify it.
+ */
+static void vcpu_do_suspend_time_adjustment(struct kvm_vcpu *vcpu,
+ u64 total_ns)
+{
+ struct kvm_lapic_irq irq = {
+ .delivery_mode = APIC_DM_FIXED,
+ .vector = HYPERVISOR_CALLBACK_VECTOR
+ };
+ u64 last_suspend_duration = 0;
+ s64 adj;
+
+ spin_lock(&vcpu->suspend_time_ns_lock);
+ if (total_ns > vcpu->suspend_time_ns) {
+ last_suspend_duration = total_ns - vcpu->suspend_time_ns;
+ vcpu->suspend_time_ns = total_ns;
+ }
+ spin_unlock(&vcpu->suspend_time_ns_lock);
+
+ if (!last_suspend_duration) {
+ /* It looks like the suspend is not happened yet. Retry. */
+ kvm_make_request(KVM_REQ_SUSPEND_TIME_ADJ, vcpu);
+ return;
+ }
+
+ adj = __this_cpu_read(cpu_tsc_khz) *
+ (last_suspend_duration / 1000000);
+ adjust_tsc_offset_host(vcpu, -adj);
+ /*
+ * This request should be processed before
+ * the first vmenter after resume to avoid
+ * an unadjusted TSC value is observed.
+ */
+ kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
+ kvm_write_suspend_time(vcpu->kvm);
+ if (!kvm_apic_set_irq(vcpu, &irq, NULL))
+ pr_err("kvm: failed to set suspend time irq\n");
+}
+
+/*
+ * Do kvm-wide suspend time adjustment (kvm-clock).
+ */
+static void kvm_do_suspend_time_adjustment(struct kvm *kvm, u64 total_ns)
+{
+ spin_lock(&kvm->suspend_time_ns_lock);
+ if (total_ns > kvm->suspend_time_ns) {
+ u64 last_suspend_duration = total_ns - kvm->suspend_time_ns;
+ /*
+ * Move the offset of kvm_clock here as if it is stopped
+ * during the suspension.
+ */
+ kvm->arch.kvmclock_offset -= last_suspend_duration;
+
+ /* suspend_time is accumulated per VM. */
+ kvm->suspend_time_ns += last_suspend_duration;
+ /*
+ * This adjustment will be reflected to the struct provided
+ * from the guest via MSR_KVM_HOST_SUSPEND_TIME before
+ * the notification interrupt is injected.
+ */
+ kvm_make_all_cpus_request(kvm, KVM_REQ_CLOCK_UPDATE);
+ }
+ spin_unlock(&kvm->suspend_time_ns_lock);
+}
+
+static void kvm_adjust_suspend_time(struct kvm_vcpu *vcpu)
+{
+ u64 total_ns = kvm_total_suspend_time(vcpu->kvm);
+ /* Do kvm-wide adjustment (kvm-clock) */
+ kvm_do_suspend_time_adjustment(vcpu->kvm, total_ns);
+ /* Do per-vcpu adjustment (tsc) */
+ vcpu_do_suspend_time_adjustment(vcpu, total_ns);
+}
+#else
+static void kvm_adjust_suspend_time(struct kvm_vcpu *vcpu)
+{
+}
+#endif
+
/*
* Returns 1 to let vcpu_run() continue the guest execution loop without
* exiting to the userspace. Otherwise, the value will be returned to the
@@ -9421,6 +9528,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
r = -EIO;
goto out;
}
+ if (kvm_check_request(KVM_REQ_SUSPEND_TIME_ADJ, vcpu))
+ kvm_adjust_suspend_time(vcpu);
if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
r = 0;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 0f18df7fe874..ef93c067ceba 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -151,6 +151,7 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_UNBLOCK 2
#define KVM_REQ_UNHALT 3
#define KVM_REQ_VM_BUGGED (4 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_SUSPEND_TIME_ADJ 5
#define KVM_REQUEST_ARCH_BASE 8

#define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
@@ -336,6 +337,11 @@ struct kvm_vcpu {
} async_pf;
#endif

+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+ u64 suspend_time_ns;
+ spinlock_t suspend_time_ns_lock;
+#endif
+
#ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
/*
* Cpu relax intercept or pause loop exit optimization
@@ -623,6 +629,12 @@ struct kvm {
struct notifier_block pm_notifier;
#endif
char stats_id[KVM_STATS_NAME_SIZE];
+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+ u64 suspend_time_ns;
+ spinlock_t suspend_time_ns_lock;
+ u64 base_offs_boot_ns;
+ struct gfn_to_hva_cache suspend_time_ghc;
+#endif
};

#define kvm_err(fmt, ...) \
@@ -1829,6 +1841,42 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
}
#endif /* CONFIG_KVM_XFER_TO_GUEST_WORK */

+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+bool virt_suspend_time_enabled(struct kvm *kvm);
+void kvm_write_suspend_time(struct kvm *kvm);
+int kvm_init_suspend_time_ghc(struct kvm *kvm, gpa_t gpa);
+static inline u64 kvm_total_suspend_time(struct kvm *kvm)
+{
+ return ktime_get_offs_boot_ns() - kvm->base_offs_boot_ns;
+}
+
+static inline u64 vcpu_suspend_time_injected(struct kvm_vcpu *vcpu)
+{
+ return vcpu->suspend_time_ns;
+}
+#else
+static inline bool virt_suspend_time_enabled(struct kvm *kvm)
+{
+ return 0;
+}
+static inline void kvm_write_suspend_time(struct kvm *kvm)
+{
+}
+static inline int kvm_init_suspend_time_ghc(struct kvm *kvm, gpa_t gpa)
+{
+ return 1;
+}
+static inline u64 kvm_total_suspend_time(struct kvm *kvm)
+{
+ return 0;
+}
+
+static inline u64 vcpu_suspend_time_injected(struct kvm_vcpu *vcpu)
+{
+ return 0;
+}
+#endif /* CONFIG_KVM_VIRT_SUSPEND_TIMING */
+
/*
* This defines how many reserved entries we want to keep before we
* kick the vcpu to the userspace to avoid dirty ring full. This
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7851f3a1b5f7..a4fedd2455d4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -425,6 +425,11 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
vcpu->ready = false;
preempt_notifier_init(&vcpu->preempt_notifier, &kvm_preempt_ops);
vcpu->last_used_slot = 0;
+
+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+ vcpu->suspend_time_ns = kvm->suspend_time_ns;
+ spin_lock_init(&vcpu->suspend_time_ns_lock);
+#endif
}

void kvm_vcpu_destroy(struct kvm_vcpu *vcpu)
@@ -812,12 +817,70 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
#endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */

#ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
+static int kvm_suspend_notifier(struct kvm *kvm)
+{
+ struct kvm_vcpu *vcpu;
+ int i;
+
+ if (!virt_suspend_time_enabled(kvm))
+ return NOTIFY_DONE;
+
+ mutex_lock(&kvm->lock);
+ kvm_for_each_vcpu(i, vcpu, kvm)
+ kvm_make_request(KVM_REQ_SUSPEND_TIME_ADJ, vcpu);
+ mutex_unlock(&kvm->lock);
+
+ return NOTIFY_DONE;
+}
+
+static int kvm_resume_notifier(struct kvm *kvm)
+{
+ struct kvm_vcpu *vcpu;
+ int i;
+
+ if (!virt_suspend_time_enabled(kvm))
+ return NOTIFY_DONE;
+
+ mutex_lock(&kvm->lock);
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ /*
+ * Clear KVM_REQ_SUSPEND_TIME_ADJ if the suspend injection is
+ * not needed (e.g. suspend failure)
+ * The following condition is also true when the adjustment is
+ * already done and it is safe to clear the request again here.
+ */
+ if (kvm_total_suspend_time(kvm) ==
+ vcpu_suspend_time_injected(vcpu))
+ kvm_clear_request(KVM_REQ_SUSPEND_TIME_ADJ, vcpu);
+ }
+ mutex_unlock(&kvm->lock);
+
+ return NOTIFY_DONE;
+}
+
+static int kvm_pm_notifier(struct kvm *kvm, unsigned long state)
+{
+ switch (state) {
+ case PM_HIBERNATION_PREPARE:
+ case PM_SUSPEND_PREPARE:
+ return kvm_suspend_notifier(kvm);
+ case PM_POST_HIBERNATION:
+ case PM_POST_SUSPEND:
+ return kvm_resume_notifier(kvm);
+ }
+
+ return NOTIFY_DONE;
+}
+
static int kvm_pm_notifier_call(struct notifier_block *bl,
unsigned long state,
void *unused)
{
struct kvm *kvm = container_of(bl, struct kvm, pm_notifier);

+ if (kvm_pm_notifier(kvm, state) != NOTIFY_DONE)
+ return NOTIFY_BAD;
+
return kvm_arch_pm_notifier(kvm, state);
}

@@ -843,6 +906,26 @@ static void kvm_destroy_pm_notifier(struct kvm *kvm)
}
#endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */

+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+void kvm_write_suspend_time(struct kvm *kvm)
+{
+ struct kvm_suspend_time st;
+
+ st.suspend_time_ns = kvm->suspend_time_ns;
+ kvm_write_guest_cached(kvm, &kvm->suspend_time_ghc, &st, sizeof(st));
+}
+
+int kvm_init_suspend_time_ghc(struct kvm *kvm, gpa_t gpa)
+{
+ if (kvm_gfn_to_hva_cache_init(kvm, &kvm->suspend_time_ghc, gpa,
+ sizeof(struct kvm_suspend_time)))
+ return 1;
+
+ kvm_write_suspend_time(kvm);
+ return 0;
+}
+#endif
+
static struct kvm_memslots *kvm_alloc_memslots(void)
{
int i;
@@ -1080,6 +1163,11 @@ static struct kvm *kvm_create_vm(unsigned long type)
if (r)
goto out_err_no_disable;

+#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
+ spin_lock_init(&kvm->suspend_time_ns_lock);
+ kvm->base_offs_boot_ns = ktime_get_offs_boot_ns();
+#endif
+
#ifdef CONFIG_HAVE_KVM_IRQFD
INIT_HLIST_HEAD(&kvm->irq_ack_notifier_list);
#endif
--
2.33.0.1079.g6e70778dc9-goog