iommu/vt-d: Put IRTE back into posted MSI mode if vCPU posting is disabled

Add a helper to take care of reconfiguring an IRTE to deliver IRQs to the
host, i.e. not to a vCPU, and use the helper when an IRTE's vCPU affinity
is nullified, i.e. when KVM puts an IRTE back into "host" mode.  Because
posted MSIs use an ephemeral IRTE, using modify_irte() puts the IRTE into
full remapped mode, i.e. unintentionally disables posted MSIs on the IRQ.

Fixes: ed1e48e ("iommu/vt-d: Enable posted mode for device MSIs")
Cc: stable@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20250315025135.2365846-2-seanjc@google.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: sean-jc

drivers/iommu/intel/irq_remapping.c

@@ -1169,7 +1169,17 @@ static void intel_ir_reconfigure_irte_posted(struct irq_data *irqd)
 static inline void intel_ir_reconfigure_irte_posted(struct irq_data *irqd) {}
 #endif
 
-static void intel_ir_reconfigure_irte(struct irq_data *irqd, bool force)
+static void __intel_ir_reconfigure_irte(struct irq_data *irqd, bool force_host)
+{
+	struct intel_ir_data *ir_data = irqd->chip_data;
+
+	if (ir_data->irq_2_iommu.posted_msi)
+		intel_ir_reconfigure_irte_posted(irqd);
+	else if (force_host || ir_data->irq_2_iommu.mode == IRQ_REMAPPING)
+		modify_irte(&ir_data->irq_2_iommu, &ir_data->irte_entry);
+}
+
+static void intel_ir_reconfigure_irte(struct irq_data *irqd, bool force_host)
 {
 	struct intel_ir_data *ir_data = irqd->chip_data;
 	struct irte *irte = &ir_data->irte_entry;
@@ -1182,10 +1192,7 @@ static void intel_ir_reconfigure_irte(struct irq_data *irqd, bool force)
 	irte->vector = cfg->vector;
 	irte->dest_id = IRTE_DEST(cfg->dest_apicid);
 
-	if (ir_data->irq_2_iommu.posted_msi)
-		intel_ir_reconfigure_irte_posted(irqd);
-	else if (force || ir_data->irq_2_iommu.mode == IRQ_REMAPPING)
-		modify_irte(&ir_data->irq_2_iommu, irte);
+	__intel_ir_reconfigure_irte(irqd, force_host);
 }
 
 /*
@@ -1240,7 +1247,7 @@ static int intel_ir_set_vcpu_affinity(struct irq_data *data, void *info)
 
 	/* stop posting interrupts, back to the default mode */
 	if (!vcpu_pi_info) {
-		modify_irte(&ir_data->irq_2_iommu, &ir_data->irte_entry);
+		__intel_ir_reconfigure_irte(data, true);
 	} else {
 		struct irte irte_pi;