[PATCH 3/6] x86/hyper-v: reenlightenment notifications support

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Hyper-V supports Live Migration notification. This is supposed to be used
in conjunction with TSC emulation: when we are migrated to a host with
different TSC frequency for some short period host emulates our accesses
to TSC and sends us an interrupt to notify about the event. When we're
done updating everything we can disable TSC emulation and everything will
start working fast again.

We didn't need these notifications before as Hyper-V guests are not
supposed to use TSC as a clocksource: in Linux we even mark it as unstable
on boot. Guests normally use 'tsc page' clocksouce and host updates its
values on migrations automatically.

Things change when we want to run nested virtualization: even when we pass
through PV clocksources (kvm-clock or tsc page) to our guests we need to
know TSC frequency and when it changes.

Hyper-V Top Level Functional Specification (as of v5.0b) wrongly specifies
EAX:BIT(12) of CPUID:0x40000009 as the feature identification bit. The
right one to check is EAX:BIT(13) of CPUID:0x40000003. I was assured that
the fix in on the way.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
RFC -> v1:
- #include <asm/apic.h> [kbuild test robot]
- use div64_u64() [kbuild test robot]
- DECLARE_WORK -> DECLARE_DELAYED_WORK as testing showed there's some bug
  in Hyper-V hypervisor and disabling emulation after receiving interrupt
  may screw TSC counters.
---
 arch/x86/entry/entry_64.S          |  4 +++
 arch/x86/hyperv/hv_init.c          | 71 ++++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/entry_arch.h  |  4 +++
 arch/x86/include/asm/hw_irq.h      |  1 +
 arch/x86/include/asm/irq_vectors.h |  7 +++-
 arch/x86/include/asm/mshyperv.h    |  8 +++++
 arch/x86/include/uapi/asm/hyperv.h | 27 +++++++++++++++
 arch/x86/kernel/idt.c              |  3 ++
 8 files changed, 124 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f81d50d7ceac..a32730b260bc 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -826,6 +826,10 @@ apicinterrupt SPURIOUS_APIC_VECTOR		spurious_interrupt		smp_spurious_interrupt
 apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
 #endif
 
+#if IS_ENABLED(CONFIG_HYPERV)
+apicinterrupt HYPERV_REENLIGHTENMENT_VECTOR	hyperv_reenlightenment_intr	smp_hyperv_reenlightenment_intr
+#endif
+
 /*
  * Exception entry points.
  */
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 1a6c63f721bc..bb62839ede81 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -18,6 +18,7 @@
  */
 
 #include <linux/types.h>
+#include <asm/apic.h>
 #include <asm/hypervisor.h>
 #include <asm/hyperv.h>
 #include <asm/mshyperv.h>
@@ -102,6 +103,76 @@ static int hv_cpu_init(unsigned int cpu)
 	return 0;
 }
 
+static void (*hv_reenlightenment_cb)(void);
+
+static void hv_reenlightenment_notify(struct work_struct *dummy)
+{
+	if (hv_reenlightenment_cb)
+		hv_reenlightenment_cb();
+}
+static DECLARE_DELAYED_WORK(hv_reenlightenment_work, hv_reenlightenment_notify);
+
+void hyperv_stop_tsc_emulation(void)
+{
+	u64 freq;
+	struct hv_tsc_emulation_status emu_status;
+
+	rdmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
+	emu_status.inprogress = 0;
+	wrmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
+
+	rdmsrl(HV_X64_MSR_TSC_FREQUENCY, freq);
+	tsc_khz = div64_u64(freq, 1000);
+}
+EXPORT_SYMBOL_GPL(hyperv_stop_tsc_emulation);
+
+void register_hv_tsc_update(void (*cb)(void))
+{
+	struct hv_reenlightenment_control re_ctrl = {
+		.vector = HYPERV_REENLIGHTENMENT_VECTOR,
+		.enabled = 1,
+		.target_vp = hv_vp_index[smp_processor_id()]
+	};
+	struct hv_tsc_emulation_control emu_ctrl = {.enabled = 1};
+
+	if (!(ms_hyperv.features & HV_X64_ACCESS_REENLIGHTENMENT))
+		return;
+
+	hv_reenlightenment_cb = cb;
+
+	/* Make sure callback is registered before we write to MSRs */
+	wmb();
+
+	wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
+	wrmsrl(HV_X64_MSR_TSC_EMULATION_CONTROL, *((u64 *)&emu_ctrl));
+}
+EXPORT_SYMBOL_GPL(register_hv_tsc_update);
+
+void unregister_hv_tsc_update(void)
+{
+	struct hv_reenlightenment_control re_ctrl;
+
+	if (!(ms_hyperv.features & HV_X64_ACCESS_REENLIGHTENMENT))
+		return;
+
+	rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *(u64 *)&re_ctrl);
+	re_ctrl.enabled = 0;
+	wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *(u64 *)&re_ctrl);
+
+	hv_reenlightenment_cb = NULL;
+}
+EXPORT_SYMBOL_GPL(unregister_hv_tsc_update);
+
+asmlinkage __visible void
+__irq_entry smp_hyperv_reenlightenment_intr(struct pt_regs *regs)
+{
+	entering_ack_irq();
+
+	schedule_delayed_work(&hv_reenlightenment_work, HZ/10);
+
+	exiting_irq();
+}
+
 /*
  * This function is to be invoked early in the boot sequence after the
  * hypervisor has been detected.
diff --git a/arch/x86/include/asm/entry_arch.h b/arch/x86/include/asm/entry_arch.h
index 416422762845..eb936cc49b62 100644
--- a/arch/x86/include/asm/entry_arch.h
+++ b/arch/x86/include/asm/entry_arch.h
@@ -54,3 +54,7 @@ BUILD_INTERRUPT(threshold_interrupt,THRESHOLD_APIC_VECTOR)
 BUILD_INTERRUPT(deferred_error_interrupt, DEFERRED_ERROR_VECTOR)
 #endif
 #endif
+
+#if IS_ENABLED(CONFIG_HYPERV)
+BUILD_INTERRUPT(hyperv_reenlightenment_intr, HYPERV_REENLIGHTENMENT_VECTOR)
+#endif
diff --git a/arch/x86/include/asm/hw_irq.h b/arch/x86/include/asm/hw_irq.h
index 2851077b6051..c65193dac7d9 100644
--- a/arch/x86/include/asm/hw_irq.h
+++ b/arch/x86/include/asm/hw_irq.h
@@ -36,6 +36,7 @@ extern asmlinkage void kvm_posted_intr_wakeup_ipi(void);
 extern asmlinkage void kvm_posted_intr_nested_ipi(void);
 extern asmlinkage void error_interrupt(void);
 extern asmlinkage void irq_work_interrupt(void);
+extern asmlinkage void hyperv_reenlightenment_intr(void);
 
 extern asmlinkage void spurious_interrupt(void);
 extern asmlinkage void thermal_interrupt(void);
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 67421f649cfa..e71c1120426b 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -103,7 +103,12 @@
 #endif
 
 #define MANAGED_IRQ_SHUTDOWN_VECTOR	0xef
-#define LOCAL_TIMER_VECTOR		0xee
+
+#if IS_ENABLED(CONFIG_HYPERV)
+#define HYPERV_REENLIGHTENMENT_VECTOR	0xee
+#endif
+
+#define LOCAL_TIMER_VECTOR		0xed
 
 #define NR_VECTORS			 256
 
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index a0b34994f453..43164b097585 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -314,11 +314,19 @@ void hyper_alloc_mmu(void);
 void hyperv_report_panic(struct pt_regs *regs, long err);
 bool hv_is_hypercall_page_setup(void);
 void hyperv_cleanup(void);
+
+asmlinkage void smp_hyperv_reenlightenment_intr(struct pt_regs *regs);
+void register_hv_tsc_update(void (*cb)(void));
+void unregister_hv_tsc_update(void);
+void hyperv_stop_tsc_emulation(void);
 #else /* CONFIG_HYPERV */
 static inline void hyperv_init(void) {}
 static inline bool hv_is_hypercall_page_setup(void) { return false; }
 static inline void hyperv_cleanup(void) {}
 static inline void hyperv_setup_mmu_ops(void) {}
+static inline void register_hv_tsc_update(void (*cb)(void)) {}
+static inline void unregister_hv_tsc_update(void) {}
+static inline void hyperv_stop_tsc_emulation(void) {};
 #endif /* CONFIG_HYPERV */
 
 #ifdef CONFIG_HYPERV_TSCPAGE
diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
index 1a5bfead93b4..197c2e6c7376 100644
--- a/arch/x86/include/uapi/asm/hyperv.h
+++ b/arch/x86/include/uapi/asm/hyperv.h
@@ -40,6 +40,9 @@
  */
 #define HV_X64_ACCESS_FREQUENCY_MSRS		(1 << 11)
 
+/* AccessReenlightenmentControls privilege */
+#define HV_X64_ACCESS_REENLIGHTENMENT		BIT(13)
+
 /*
  * Basic SynIC MSRs (HV_X64_MSR_SCONTROL through HV_X64_MSR_EOM
  * and HV_X64_MSR_SINT0 through HV_X64_MSR_SINT15) available
@@ -234,6 +237,30 @@
 #define HV_X64_MSR_CRASH_PARAMS		\
 		(1 + (HV_X64_MSR_CRASH_P4 - HV_X64_MSR_CRASH_P0))
 
+/* TSC emulation after migration */
+#define HV_X64_MSR_REENLIGHTENMENT_CONTROL	0x40000106
+
+struct hv_reenlightenment_control {
+	u64 vector:8;
+	u64 reserved1:8;
+	u64 enabled:1;
+	u64 reserved2:15;
+	u64 target_vp:32;
+};
+
+#define HV_X64_MSR_TSC_EMULATION_CONTROL	0x40000107
+#define HV_X64_MSR_TSC_EMULATION_STATUS		0x40000108
+
+struct hv_tsc_emulation_control {
+	u64 enabled:1;
+	u64 reserved:63;
+};
+
+struct hv_tsc_emulation_status {
+	u64 inprogress:1;
+	u64 reserved:63;
+};
+
 #define HV_X64_MSR_HYPERCALL_ENABLE		0x00000001
 #define HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_SHIFT	12
 #define HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_MASK	\
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index d985cef3984f..5b8512d48aa3 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -140,6 +140,9 @@ static const __initdata struct idt_data apic_idts[] = {
 # ifdef CONFIG_IRQ_WORK
 	INTG(IRQ_WORK_VECTOR,		irq_work_interrupt),
 # endif
+#if IS_ENABLED(CONFIG_HYPERV)
+	INTG(HYPERV_REENLIGHTENMENT_VECTOR, hyperv_reenlightenment_intr),
+#endif
 	INTG(SPURIOUS_APIC_VECTOR,	spurious_interrupt),
 	INTG(ERROR_APIC_VECTOR,		error_interrupt),
 #endif
-- 
2.14.3