iommu/vt-d: Don't clobber posted vCPU IRTE when host IRQ affinity changes

Don't overwrite an IRTE that is posting IRQs to a vCPU with a posted MSI
entry if the host IRQ affinity happens to change.  If/when the IRTE is
reverted back to "host mode", it will be reconfigured as a posted MSI or
remapped entry as appropriate.

Drop the "mode" field, which doesn't differentiate between posted MSIs and
posted vCPUs, in favor of a dedicated posted_vcpu flag.  Note!  The two
posted_{msi,vcpu} flags are intentionally not mutually exclusive; an IRTE
can transition between posted MSI and posted vCPU.

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/20250315025135.2365846-3-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

@@ -25,11 +25,6 @@
 #include "../irq_remapping.h"
 #include "../iommu-pages.h"
 
-enum irq_mode {
-	IRQ_REMAPPING,
-	IRQ_POSTING,
-};
-
 struct ioapic_scope {
 	struct intel_iommu *iommu;
 	unsigned int id;
@@ -49,8 +44,8 @@ struct irq_2_iommu {
 	u16 irte_index;
 	u16 sub_handle;
 	u8  irte_mask;
-	enum irq_mode mode;
 	bool posted_msi;
+	bool posted_vcpu;
 };
 
 struct intel_ir_data {
@@ -138,7 +133,6 @@ static int alloc_irte(struct intel_iommu *iommu,
 		irq_iommu->irte_index =  index;
 		irq_iommu->sub_handle = 0;
 		irq_iommu->irte_mask = mask;
-		irq_iommu->mode = IRQ_REMAPPING;
 	}
 	raw_spin_unlock_irqrestore(&irq_2_ir_lock, flags);
 
@@ -193,8 +187,6 @@ static int modify_irte(struct irq_2_iommu *irq_iommu,
 
 	rc = qi_flush_iec(iommu, index, 0);
 
-	/* Update iommu mode according to the IRTE mode */
-	irq_iommu->mode = irte->pst ? IRQ_POSTING : IRQ_REMAPPING;
 	raw_spin_unlock_irqrestore(&irq_2_ir_lock, flags);
 
 	return rc;
@@ -1173,9 +1165,18 @@ static void __intel_ir_reconfigure_irte(struct irq_data *irqd, bool force_host)
 {
 	struct intel_ir_data *ir_data = irqd->chip_data;
 
+	/*
+	 * Don't modify IRTEs for IRQs that are being posted to vCPUs if the
+	 * host CPU affinity changes.
+	 */
+	if (ir_data->irq_2_iommu.posted_vcpu && !force_host)
+		return;
+
+	ir_data->irq_2_iommu.posted_vcpu = false;
+
 	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)
+	else
 		modify_irte(&ir_data->irq_2_iommu, &ir_data->irte_entry);
 }
 
@@ -1270,6 +1271,7 @@ static int intel_ir_set_vcpu_affinity(struct irq_data *data, void *info)
 		irte_pi.pda_h = (vcpu_pi_info->pi_desc_addr >> 32) &
 				~(-1UL << PDA_HIGH_BIT);
 
+		ir_data->irq_2_iommu.posted_vcpu = true;
 		modify_irte(&ir_data->irq_2_iommu, &irte_pi);
 	}
 
@@ -1496,6 +1498,9 @@ static void intel_irq_remapping_deactivate(struct irq_domain *domain,
 	struct intel_ir_data *data = irq_data->chip_data;
 	struct irte entry;
 
+	WARN_ON_ONCE(data->irq_2_iommu.posted_vcpu);
+	data->irq_2_iommu.posted_vcpu = false;
+
 	memset(&entry, 0, sizeof(entry));
 	modify_irte(&data->irq_2_iommu, &entry);
 }