KVM: x86: interrupt based APF 'page ready' event delivery

Concerns were expressed around APF delivery via synthetic #PF exception as
in some cases such delivery may collide with real page fault. For 'page
ready' notifications we can easily switch to using an interrupt instead.
Introduce new MSR_KVM_ASYNC_PF_INT mechanism and deprecate the legacy one.

One notable difference between the two mechanisms is that interrupt may not
get handled immediately so whenever we would like to deliver next event
(regardless of its type) we must be sure the guest had read and cleared
previous event in the slot.

While on it, get rid on 'type 1/type 2' names for APF events in the
documentation as they are causing confusion. Use 'page not present'
and 'page ready' everywhere instead.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200525144125.143875-6-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 67 insertions, 26 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0e79b37b2b7e..e6f3ec5193b2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1248,7 +1248,7 @@ static const u32 emulated_msrs_all[] = {
 	HV_X64_MSR_TSC_EMULATION_STATUS,
 
 	MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
-	MSR_KVM_PV_EOI_EN,
+	MSR_KVM_PV_EOI_EN, MSR_KVM_ASYNC_PF_INT,
 
 	MSR_IA32_TSC_ADJUST,
 	MSR_IA32_TSCDEADLINE,
@@ -2673,17 +2673,24 @@ out:
 	return r;
 }
 
+static inline bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu)
+{
+	u64 mask = KVM_ASYNC_PF_ENABLED | KVM_ASYNC_PF_DELIVERY_AS_INT;
+
+	return (vcpu->arch.apf.msr_en_val & mask) == mask;
+}
+
 static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
 {
 	gpa_t gpa = data & ~0x3f;
 
-	/* Bits 3:5 are reserved, Should be zero */
-	if (data & 0x38)
+	/* Bits 4:5 are reserved, Should be zero */
+	if (data & 0x30)
 		return 1;
 
-	vcpu->arch.apf.msr_val = data;
+	vcpu->arch.apf.msr_en_val = data;
 
-	if (!(data & KVM_ASYNC_PF_ENABLED)) {
+	if (!kvm_pv_async_pf_enabled(vcpu)) {
 		kvm_clear_async_pf_completion_queue(vcpu);
 		kvm_async_pf_hash_reset(vcpu);
 		return 0;
@@ -2695,7 +2702,25 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
 
 	vcpu->arch.apf.send_user_only = !(data & KVM_ASYNC_PF_SEND_ALWAYS);
 	vcpu->arch.apf.delivery_as_pf_vmexit = data & KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT;
+
 	kvm_async_pf_wakeup_all(vcpu);
+
+	return 0;
+}
+
+static int kvm_pv_enable_async_pf_int(struct kvm_vcpu *vcpu, u64 data)
+{
+	/* Bits 8-63 are reserved */
+	if (data >> 8)
+		return 1;
+
+	if (!lapic_in_kernel(vcpu))
+		return 1;
+
+	vcpu->arch.apf.msr_int_val = data;
+
+	vcpu->arch.apf.vec = data & KVM_ASYNC_PF_VEC_MASK;
+
 	return 0;
 }
 
@@ -2917,6 +2942,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (kvm_pv_enable_async_pf(vcpu, data))
 			return 1;
 		break;
+	case MSR_KVM_ASYNC_PF_INT:
+		if (kvm_pv_enable_async_pf_int(vcpu, data))
+			return 1;
+		break;
 	case MSR_KVM_STEAL_TIME:
 
 		if (unlikely(!sched_info_on()))
@@ -3191,7 +3220,10 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = vcpu->arch.time;
 		break;
 	case MSR_KVM_ASYNC_PF_EN:
-		msr_info->data = vcpu->arch.apf.msr_val;
+		msr_info->data = vcpu->arch.apf.msr_en_val;
+		break;
+	case MSR_KVM_ASYNC_PF_INT:
+		msr_info->data = vcpu->arch.apf.msr_int_val;
 		break;
 	case MSR_KVM_STEAL_TIME:
 		msr_info->data = vcpu->arch.st.msr_val;
@@ -9553,7 +9585,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	vcpu->arch.cr2 = 0;
 
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
-	vcpu->arch.apf.msr_val = 0;
+	vcpu->arch.apf.msr_en_val = 0;
+	vcpu->arch.apf.msr_int_val = 0;
 	vcpu->arch.st.msr_val = 0;
 
 	kvmclock_reset(vcpu);
@@ -10430,10 +10463,22 @@ static inline int apf_put_user_notpresent(struct kvm_vcpu *vcpu)
 
 static inline int apf_put_user_ready(struct kvm_vcpu *vcpu, u32 token)
 {
-	u64 val = (u64)token << 32 | KVM_PV_REASON_PAGE_READY;
+	unsigned int offset = offsetof(struct kvm_vcpu_pv_apf_data, token);
 
-	return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.apf.data, &val,
-				      sizeof(val));
+	return kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.apf.data,
+					     &token, offset, sizeof(token));
+}
+
+static inline bool apf_pageready_slot_free(struct kvm_vcpu *vcpu)
+{
+	unsigned int offset = offsetof(struct kvm_vcpu_pv_apf_data, token);
+	u32 val;
+
+	if (kvm_read_guest_offset_cached(vcpu->kvm, &vcpu->arch.apf.data,
+					 &val, offset, sizeof(val)))
+		return false;
+
+	return !val;
 }
 
 static bool kvm_can_deliver_async_pf(struct kvm_vcpu *vcpu)
@@ -10441,9 +10486,8 @@ static bool kvm_can_deliver_async_pf(struct kvm_vcpu *vcpu)
 	if (!vcpu->arch.apf.delivery_as_pf_vmexit && is_guest_mode(vcpu))
 		return false;
 
-	if (!(vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED) ||
-	    (vcpu->arch.apf.send_user_only &&
-	     kvm_x86_ops.get_cpl(vcpu) == 0))
+	if (!kvm_pv_async_pf_enabled(vcpu) ||
+	    (vcpu->arch.apf.send_user_only && kvm_x86_ops.get_cpl(vcpu) == 0))
 		return false;
 
 	return true;
@@ -10499,7 +10543,10 @@ void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
 void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
 				 struct kvm_async_pf *work)
 {
-	struct x86_exception fault;
+	struct kvm_lapic_irq irq = {
+		.delivery_mode = APIC_DM_FIXED,
+		.vector = vcpu->arch.apf.vec
+	};
 
 	if (work->wakeup_all)
 		work->arch.token = ~0; /* broadcast wakeup */
@@ -10507,26 +10554,20 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
 		kvm_del_async_pf_gfn(vcpu, work->arch.gfn);
 	trace_kvm_async_pf_ready(work->arch.token, work->cr2_or_gpa);
 
-	if (vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED &&
-	    !apf_put_user_ready(vcpu, work->arch.token)) {
-			fault.vector = PF_VECTOR;
-			fault.error_code_valid = true;
-			fault.error_code = 0;
-			fault.nested_page_fault = false;
-			fault.address = work->arch.token;
-			fault.async_page_fault = true;
-			kvm_inject_page_fault(vcpu, &fault);
-	}
+	if (kvm_pv_async_pf_enabled(vcpu) &&
+	    !apf_put_user_ready(vcpu, work->arch.token))
+		kvm_apic_set_irq(vcpu, &irq, NULL);
+
 	vcpu->arch.apf.halted = false;
 	vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
 }
 
 bool kvm_arch_can_dequeue_async_page_present(struct kvm_vcpu *vcpu)
 {
-	if (!(vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED))
+	if (!kvm_pv_async_pf_enabled(vcpu))
 		return true;
 	else
-		return kvm_can_do_async_pf(vcpu);
+		return apf_pageready_slot_free(vcpu);
 }
 
 void kvm_arch_start_assignment(struct kvm *kvm)