KVM: x86: Use a stable condition around all VT-d PI paths

Currently, checks for whether VT-d PI can be used refer to the current
status of the feature in the current vCPU; or they more or less pick
vCPU 0 in case a specific vCPU is not available.

However, these checks do not attempt to synchronize with changes to
the IRTE.  In particular, there is no path that updates the IRTE when
APICv is re-activated on vCPU 0; and there is no path to wakeup a CPU
that has APICv disabled, if the wakeup occurs because of an IRTE
that points to a posted interrupt.

To fix this, always go through the VT-d PI path as long as there are
assigned devices and APICv is available on both the host and the VM side.
Since the relevant condition was copied over three times, take the hint
and factor it into a separate function.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: stable@vger.kernel.org
Reviewed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Message-Id: <20211123004311.2954158-5-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/posted_intr.c

@@ -5,6 +5,7 @@
 #include <asm/cpu.h>
 
 #include "lapic.h"
+#include "irq.h"
 #include "posted_intr.h"
 #include "trace.h"
 #include "vmx.h"
@@ -77,13 +78,18 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
 		pi_set_on(pi_desc);
 }
 
+static bool vmx_can_use_vtd_pi(struct kvm *kvm)
+{
+	return irqchip_in_kernel(kvm) && enable_apicv &&
+		kvm_arch_has_assigned_device(kvm) &&
+		irq_remapping_cap(IRQ_POSTING_CAP);
+}
+
 void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
 {
 	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
 
-	if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
-		!irq_remapping_cap(IRQ_POSTING_CAP)  ||
-		!kvm_vcpu_apicv_active(vcpu))
+	if (!vmx_can_use_vtd_pi(vcpu->kvm))
 		return;
 
 	/* Set SN when the vCPU is preempted */
@@ -141,9 +147,7 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
 	struct pi_desc old, new;
 	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
 
-	if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
-		!irq_remapping_cap(IRQ_POSTING_CAP)  ||
-		!kvm_vcpu_apicv_active(vcpu))
+	if (!vmx_can_use_vtd_pi(vcpu->kvm))
 		return 0;
 
 	WARN_ON(irqs_disabled());
@@ -270,9 +274,7 @@ int pi_update_irte(struct kvm *kvm, unsigned int host_irq, uint32_t guest_irq,
 	struct vcpu_data vcpu_info;
 	int idx, ret = 0;
 
-	if (!kvm_arch_has_assigned_device(kvm) ||
-	    !irq_remapping_cap(IRQ_POSTING_CAP) ||
-	    !kvm_vcpu_apicv_active(kvm->vcpus[0]))
+	if (!vmx_can_use_vtd_pi(kvm))
 		return 0;
 
 	idx = srcu_read_lock(&kvm->irq_srcu);