[PATCH] KVM: x86: Convert INIT and SIPI signals into synchronously handled events

[Jan Kiszka <jan.kiszka@siemens.com>]

A VCPU sending INIT or SIPI to some other VCPU races for setting the
remote VCPU's mp_state. When we were unlucky, KVM_MP_STATE_INIT_RECEIVED
was overwritten by kvm_emulate_halt and, thus, got lost.

This introduces APIC events for those two signals, keeping them in
kvm_apic until kvm_apic_accept_events is run over the target vcpu
context. kvm_apic_has_events reports to kvm_arch_vcpu_runnable if there
are pending events, thus if vcpu blocking should end.

The patch comes with the side effect of effectively obsoleting
KVM_MP_STATE_SIPI_RECEIVED. We still accept it from user space, but
immediately translate it to KVM_MP_STATE_INIT_RECEIVED + KVM_APIC_SIPI.
The vcpu itself will no longer enter the KVM_MP_STATE_SIPI_RECEIVED
state. That also means we no longer exit to user space after receiving a
SIPI event.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

This doesn't fix the wrong behaviour on INIT for the BSP yet. Leaving
this honor to Paolo.

I didn't try porting any INIT handling for nested on top yet but I
think it should be feasible - once we know their semantics for sure, at
least on Intel...

 arch/x86/include/asm/kvm_host.h |    1 +
 arch/x86/kvm/lapic.c            |   41 +++++++++++++++++++++++++++++++-------
 arch/x86/kvm/lapic.h            |    7 ++++++
 arch/x86/kvm/x86.c              |   39 ++++++++++++++++++++----------------
 4 files changed, 63 insertions(+), 25 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 348d859..2d28e76 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1002,6 +1002,7 @@ int kvm_cpu_has_injectable_intr(struct kvm_vcpu *v);
 int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
 int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu);
 int kvm_cpu_get_interrupt(struct kvm_vcpu *v);
+void kvm_vcpu_reset(struct kvm_vcpu *vcpu);
 
 void kvm_define_shared_msr(unsigned index, u32 msr);
 void kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 02b51dd..4a21a6b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -731,7 +731,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
 	case APIC_DM_INIT:
 		if (!trig_mode || level) {
 			result = 1;
-			vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
+			set_bit(KVM_APIC_INIT, &apic->pending_events);
 			kvm_make_request(KVM_REQ_EVENT, vcpu);
 			kvm_vcpu_kick(vcpu);
 		} else {
@@ -743,13 +743,13 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
 	case APIC_DM_STARTUP:
 		apic_debug("SIPI to vcpu %d vector 0x%02x\n",
 			   vcpu->vcpu_id, vector);
-		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
-			result = 1;
-			vcpu->arch.sipi_vector = vector;
-			vcpu->arch.mp_state = KVM_MP_STATE_SIPI_RECEIVED;
-			kvm_make_request(KVM_REQ_EVENT, vcpu);
-			kvm_vcpu_kick(vcpu);
-		}
+		result = 1;
+		apic->sipi_vector = vector;
+		/* make sure sipi_vector is visible for the receiver */
+		smp_wmb();
+		set_bit(KVM_APIC_SIPI, &apic->pending_events);
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
+		kvm_vcpu_kick(vcpu);
 		break;
 
 	case APIC_DM_EXTINT:
@@ -1860,6 +1860,31 @@ int kvm_lapic_enable_pv_eoi(struct kvm_vcpu *vcpu, u64 data)
 					 addr);
 }
 
+bool kvm_apic_has_events(struct kvm_vcpu *vcpu)
+{
+	return kvm_vcpu_has_lapic(vcpu) && vcpu->arch.apic->pending_events;
+}
+
+void kvm_apic_accept_events(struct kvm_vcpu *vcpu)
+{
+	struct kvm_lapic *apic = vcpu->arch.apic;
+
+	if (!kvm_vcpu_has_lapic(vcpu))
+		return;
+
+	if (test_and_clear_bit(KVM_APIC_INIT, &apic->pending_events))
+		vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
+	if (test_and_clear_bit(KVM_APIC_SIPI, &apic->pending_events) &&
+	    vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
+		vcpu->arch.sipi_vector = apic->sipi_vector;
+		pr_debug("vcpu %d received sipi with vector # %x\n",
+			 vcpu->vcpu_id, vcpu->arch.sipi_vector);
+		kvm_lapic_reset(vcpu);
+		kvm_vcpu_reset(vcpu);
+		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
+	}
+}
+
 void kvm_lapic_init(void)
 {
 	/* do not patch jump label more than once per second */
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 1676d34..ef3f4ef 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -5,6 +5,9 @@
 
 #include <linux/kvm_host.h>
 
+#define KVM_APIC_INIT		0
+#define KVM_APIC_SIPI		1
+
 struct kvm_timer {
 	struct hrtimer timer;
 	s64 period; 				/* unit: ns */
@@ -32,13 +35,17 @@ struct kvm_lapic {
 	void *regs;
 	gpa_t vapic_addr;
 	struct page *vapic_page;
+	unsigned long pending_events;
+	unsigned int sipi_vector;
 };
 int kvm_create_lapic(struct kvm_vcpu *vcpu);
 void kvm_free_lapic(struct kvm_vcpu *vcpu);
 
 int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu);
+bool kvm_apic_has_events(struct kvm_vcpu *vcpu);
 int kvm_apic_accept_pic_intr(struct kvm_vcpu *vcpu);
 int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu);
+void kvm_apic_accept_events(struct kvm_vcpu *vcpu);
 void kvm_lapic_reset(struct kvm_vcpu *vcpu);
 u64 kvm_lapic_get_cr8(struct kvm_vcpu *vcpu);
 void kvm_lapic_set_tpr(struct kvm_vcpu *vcpu, unsigned long cr8);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b891ac3..a0b8041 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -162,8 +162,6 @@ u64 __read_mostly host_xcr0;
 
 static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt);
 
-static void kvm_vcpu_reset(struct kvm_vcpu *vcpu);
-
 static inline void kvm_async_pf_hash_reset(struct kvm_vcpu *vcpu)
 {
 	int i;
@@ -5663,6 +5661,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	bool req_immediate_exit = 0;
 
 	if (vcpu->requests) {
+		kvm_apic_accept_events(vcpu);
+		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
+			r = 1;
+			goto out;
+		}
 		if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
 			kvm_mmu_unload(vcpu);
 		if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
@@ -5847,14 +5850,6 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 	int r;
 	struct kvm *kvm = vcpu->kvm;
 
-	if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED)) {
-		pr_debug("vcpu %d received sipi with vector # %x\n",
-			 vcpu->vcpu_id, vcpu->arch.sipi_vector);
-		kvm_lapic_reset(vcpu);
-		kvm_vcpu_reset(vcpu);
-		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
-	}
-
 	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
 	r = vapic_enter(vcpu);
 	if (r) {
@@ -5871,8 +5866,8 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
 			kvm_vcpu_block(vcpu);
 			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
-			if (kvm_check_request(KVM_REQ_UNHALT, vcpu))
-			{
+			if (kvm_check_request(KVM_REQ_UNHALT, vcpu)) {
+				kvm_apic_accept_events(vcpu);
 				switch(vcpu->arch.mp_state) {
 				case KVM_MP_STATE_HALTED:
 					vcpu->arch.mp_state =
@@ -5880,7 +5875,8 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 				case KVM_MP_STATE_RUNNABLE:
 					vcpu->arch.apf.halted = false;
 					break;
-				case KVM_MP_STATE_SIPI_RECEIVED:
+				case KVM_MP_STATE_INIT_RECEIVED:
+					break;
 				default:
 					r = -EINTR;
 					break;
@@ -5901,7 +5897,8 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 			++vcpu->stat.request_irq_exits;
 		}
 
-		kvm_check_async_pf_completion(vcpu);
+		if (vcpu->arch.mp_state != KVM_MP_STATE_INIT_RECEIVED)
+			kvm_check_async_pf_completion(vcpu);
 
 		if (signal_pending(current)) {
 			r = -EINTR;
@@ -6015,6 +6012,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 
 	if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
 		kvm_vcpu_block(vcpu);
+		kvm_apic_accept_events(vcpu);
 		clear_bit(KVM_REQ_UNHALT, &vcpu->requests);
 		r = -EAGAIN;
 		goto out;
@@ -6171,6 +6169,7 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
 int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
 				    struct kvm_mp_state *mp_state)
 {
+	kvm_apic_accept_events(vcpu);
 	mp_state->mp_state = vcpu->arch.mp_state;
 	return 0;
 }
@@ -6178,7 +6177,13 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
 int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 				    struct kvm_mp_state *mp_state)
 {
-	vcpu->arch.mp_state = mp_state->mp_state;
+	if (mp_state->mp_state == KVM_MP_STATE_SIPI_RECEIVED) {
+		if (!kvm_vcpu_has_lapic(vcpu))
+			return -EINVAL;
+		vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
+		set_bit(KVM_APIC_SIPI, &vcpu->arch.apic->pending_events);
+	} else
+		vcpu->arch.mp_state = mp_state->mp_state;
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
 	return 0;
 }
@@ -6515,7 +6520,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 	kvm_x86_ops->vcpu_free(vcpu);
 }
 
-static void kvm_vcpu_reset(struct kvm_vcpu *vcpu)
+void kvm_vcpu_reset(struct kvm_vcpu *vcpu)
 {
 	atomic_set(&vcpu->arch.nmi_queued, 0);
 	vcpu->arch.nmi_pending = 0;
@@ -6988,7 +6993,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
 	return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
 		!vcpu->arch.apf.halted)
 		|| !list_empty_careful(&vcpu->async_pf.done)
-		|| vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED
+		|| kvm_apic_has_events(vcpu)
 		|| atomic_read(&vcpu->arch.nmi_queued) ||
 		(kvm_arch_interrupt_allowed(vcpu) &&
 		 kvm_cpu_has_interrupt(vcpu));
-- 
1.7.3.4