KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()

'vector' and 'trig_mode' fields of 'struct kvm_lapic_irq' are left
uninitialized in kvm_pv_kick_cpu_op(). While these fields are normally
not needed for APIC_DM_REMRD, they're still referenced by
__apic_accept_irq() for trace_kvm_apic_accept_irq(). Fully initialize
the structure to avoid consuming random stack memory.

Fixes: a183b638 ("KVM: x86: make apic_accept_irq tracepoint more generic")
Reported-by: syzbot+d6caa905917d353f0d07@syzkaller.appspotmail.com
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220708125147.593975-1-vkuznets@redhat.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/x86.c

@@ -9340,15 +9340,17 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
  */
 static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
 {
-	struct kvm_lapic_irq lapic_irq;
-
-	lapic_irq.shorthand = APIC_DEST_NOSHORT;
-	lapic_irq.dest_mode = APIC_DEST_PHYSICAL;
-	lapic_irq.level = 0;
-	lapic_irq.dest_id = apicid;
-	lapic_irq.msi_redir_hint = false;
+	/*
+	 * All other fields are unused for APIC_DM_REMRD, but may be consumed by
+	 * common code, e.g. for tracing. Defer initialization to the compiler.
+	 */
+	struct kvm_lapic_irq lapic_irq = {
+		.delivery_mode = APIC_DM_REMRD,
+		.dest_mode = APIC_DEST_PHYSICAL,
+		.shorthand = APIC_DEST_NOSHORT,
+		.dest_id = apicid,
+	};
 
-	lapic_irq.delivery_mode = APIC_DM_REMRD;
 	kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
 }