[PATCH v11 075/113] KVM: TDX: Add support for find pending IRQ in a protected local APIC

[isaku . yamahata]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

Add flag and hook to KVM's local APIC management to support determining
whether or not a TDX guest as a pending IRQ.  For TDX vCPUs, the virtual
APIC page is owned by the TDX module and cannot be accessed by KVM.  As a
result, registers that are virtualized by the CPU, e.g. PPR, cannot be
read or written by KVM.  To deliver interrupts for TDX guests, KVM must
send an IRQ to the CPU on the posted interrupt notification vector.  And
to determine if TDX vCPU has a pending interrupt, KVM must check if there
is an outstanding notification.

Return "no interrupt" in kvm_apic_has_interrupt() if the guest APIC is
protected to short-circuit the various other flows that try to pull an
IRQ out of the vAPIC, the only valid operation is querying _if_ an IRQ is
pending, KVM can't do anything based on _which_ IRQ is pending.

Intentionally omit sanity checks from other flows, e.g. PPR update, so as
not to degrade non-TDX guests with unnecessary checks.  A well-behaved KVM
and userspace will never reach those flows for TDX guests, but reaching
them is not fatal if something does go awry.

Note, this doesn't handle interrupts that have been delivered to the vCPU
but not yet recognized by the core, i.e. interrupts that are sitting in
vmcs.GUEST_INTR_STATUS.  Querying that state requires a SEAMCALL and will
be supported in a future patch.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 arch/x86/include/asm/kvm-x86-ops.h |  1 +
 arch/x86/include/asm/kvm_host.h    |  1 +
 arch/x86/kvm/irq.c                 |  3 +++
 arch/x86/kvm/lapic.c               |  3 +++
 arch/x86/kvm/lapic.h               |  2 ++
 arch/x86/kvm/vmx/main.c            | 11 +++++++++++
 arch/x86/kvm/vmx/tdx.c             |  6 ++++++
 arch/x86/kvm/vmx/x86_ops.h         |  2 ++
 8 files changed, 29 insertions(+)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 99ac85c3c8aa..aeff96543090 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -117,6 +117,7 @@ KVM_X86_OP_OPTIONAL(pi_update_irte)
 KVM_X86_OP_OPTIONAL(pi_start_assignment)
 KVM_X86_OP_OPTIONAL(apicv_post_state_restore)
 KVM_X86_OP_OPTIONAL_RET0(dy_apicv_has_pending_interrupt)
+KVM_X86_OP_OPTIONAL(protected_apic_has_interrupt)
 KVM_X86_OP_OPTIONAL(set_hv_timer)
 KVM_X86_OP_OPTIONAL(cancel_hv_timer)
 KVM_X86_OP(setup_mce)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 908911e6f0ba..cead782a48b6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1738,6 +1738,7 @@ struct kvm_x86_ops {
 	void (*pi_start_assignment)(struct kvm *kvm);
 	void (*apicv_post_state_restore)(struct kvm_vcpu *vcpu);
 	bool (*dy_apicv_has_pending_interrupt)(struct kvm_vcpu *vcpu);
+	bool (*protected_apic_has_interrupt)(struct kvm_vcpu *vcpu);
 
 	int (*set_hv_timer)(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc,
 			    bool *expired);
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index b2c397dd2bc6..fd6af5530c32 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -100,6 +100,9 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
 	if (kvm_cpu_has_extint(v))
 		return 1;
 
+	if (lapic_in_kernel(v) && v->arch.apic->guest_apic_protected)
+		return static_call(kvm_x86_protected_apic_has_interrupt)(v);
+
 	return kvm_apic_has_interrupt(v) != -1;	/* LAPIC */
 }
 EXPORT_SYMBOL_GPL(kvm_cpu_has_interrupt);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index cfaf1d8c64ca..9e8d768ce83f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2623,6 +2623,9 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
 	if (!kvm_apic_present(vcpu))
 		return -1;
 
+	if (apic->guest_apic_protected)
+		return -1;
+
 	__apic_update_ppr(apic, &ppr);
 	return apic_has_interrupt_for_ppr(apic, ppr);
 }
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 58c3242fcc7a..79075164e96b 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -66,6 +66,8 @@ struct kvm_lapic {
 	bool sw_enabled;
 	bool irr_pending;
 	bool lvt0_in_nmi_mode;
+	/* Select registers in the vAPIC cannot be read/written. */
+	bool guest_apic_protected;
 	/* Number of bits set in ISR. */
 	s16 isr_count;
 	/* The highest vector set in ISR; if -1 - invalid, must scan ISR. */
diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 7be68c3b345b..91696d5d183f 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -34,6 +34,9 @@ static __init int vt_hardware_setup(void)
 
 	enable_tdx = enable_tdx && !tdx_hardware_setup(&vt_x86_ops);
 
+	if (!enable_tdx)
+		vt_x86_ops.protected_apic_has_interrupt = NULL;
+
 	if (enable_ept)
 		kvm_mmu_set_ept_masks(enable_ept_ad_bits,
 				      cpu_has_vmx_ept_execute_only());
@@ -156,6 +159,13 @@ static void vt_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	return vmx_vcpu_load(vcpu, cpu);
 }
 
+static bool vt_protected_apic_has_interrupt(struct kvm_vcpu *vcpu)
+{
+	KVM_BUG_ON(!is_td_vcpu(vcpu), vcpu->kvm);
+
+	return tdx_protected_apic_has_interrupt(vcpu);
+}
+
 static void vt_flush_tlb_all(struct kvm_vcpu *vcpu)
 {
 	if (is_td_vcpu(vcpu))
@@ -336,6 +346,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
 	.sync_pir_to_irr = vmx_sync_pir_to_irr,
 	.deliver_interrupt = vmx_deliver_interrupt,
 	.dy_apicv_has_pending_interrupt = pi_has_pending_interrupt,
+	.protected_apic_has_interrupt = vt_protected_apic_has_interrupt,
 
 	.set_tss_addr = vmx_set_tss_addr,
 	.set_identity_map_addr = vmx_set_identity_map_addr,
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 9158d266a086..3f444e138f52 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -474,6 +474,7 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
 		return -EINVAL;
 
 	fpstate_set_confidential(&vcpu->arch.guest_fpu);
+	vcpu->arch.apic->guest_apic_protected = true;
 
 	vcpu->arch.efer = EFER_SCE | EFER_LME | EFER_LMA | EFER_NX;
 
@@ -512,6 +513,11 @@ void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	local_irq_enable();
 }
 
+bool tdx_protected_apic_has_interrupt(struct kvm_vcpu *vcpu)
+{
+	return pi_has_pending_interrupt(vcpu);
+}
+
 void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_tdx *tdx = to_tdx(vcpu);
diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
index dbbc27519637..32e045480bdb 100644
--- a/arch/x86/kvm/vmx/x86_ops.h
+++ b/arch/x86/kvm/vmx/x86_ops.h
@@ -161,6 +161,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu);
 void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
 void tdx_vcpu_put(struct kvm_vcpu *vcpu);
 void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
+bool tdx_protected_apic_has_interrupt(struct kvm_vcpu *vcpu);
 u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
 
 int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
@@ -190,6 +191,7 @@ static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) { return EXIT_FASTP
 static inline void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) {}
 static inline void tdx_vcpu_put(struct kvm_vcpu *vcpu) {}
 static inline void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) {}
+static inline bool tdx_protected_apic_has_interrupt(struct kvm_vcpu *vcpu) { return false; }
 static inline u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) { return 0; }
 
 static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOPNOTSUPP; }
-- 
2.25.1