KVM: VMX: Assert that IRQs are disabled when putting vCPU on PI wakeup list

Assert that IRQs are already disabled when putting a vCPU on a CPU's PI
wakeup list, as opposed to saving/disabling+restoring IRQs.  KVM relies on
IRQs being disabled until the vCPU task is fully scheduled out, i.e. until
the scheduler has dropped all of its per-CPU locks (e.g. for the runqueue),
as attempting to wake the task while it's being scheduled out could lead
to deadlock.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Message-ID: <20250401154727.835231-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: sean-jc

arch/x86/kvm/vmx/posted_intr.c

@@ -148,9 +148,8 @@ static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)
 	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct pi_desc old, new;
-	unsigned long flags;
 
-	local_irq_save(flags);
+	lockdep_assert_irqs_disabled();
 
 	raw_spin_lock(&per_cpu(wakeup_vcpus_on_cpu_lock, vcpu->cpu));
 	list_add_tail(&vmx->pi_wakeup_list,
@@ -176,8 +175,6 @@ static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)
 	 */
 	if (pi_test_on(&new))
 		__apic_send_IPI_self(POSTED_INTR_WAKEUP_VECTOR);
-
-	local_irq_restore(flags);
 }
 
 static bool vmx_needs_pi_wakeup(struct kvm_vcpu *vcpu)