iommu/amd: WARN if KVM calls GA IRTE helpers without virtual APIC support

WARN if KVM attempts to update IRTE entries when virtual APIC isn't fully
supported, as KVM should guard all such calls on IRQ posting being enabled.

Link: https://lore.kernel.org/r/20250611224604.313496-58-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

drivers/iommu/amd/iommu.c

@@ -3836,8 +3836,10 @@ int amd_iommu_update_ga(int cpu, void *data)
 	struct amd_ir_data *ir_data = (struct amd_ir_data *)data;
 	struct irte_ga *entry = (struct irte_ga *) ir_data->entry;
 
-	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
-	    !entry || !entry->lo.fields_vapic.guest_mode)
+	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
+		return -EINVAL;
+
+	if (!entry || !entry->lo.fields_vapic.guest_mode)
 		return 0;
 
 	if (!ir_data->iommu)
@@ -3856,7 +3858,10 @@ int amd_iommu_activate_guest_mode(void *data, int cpu)
 	struct irte_ga *entry = (struct irte_ga *) ir_data->entry;
 	u64 valid;
 
-	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) || !entry)
+	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
+		return -EINVAL;
+
+	if (!entry)
 		return 0;
 
 	valid = entry->lo.fields_vapic.valid;
@@ -3885,8 +3890,10 @@ int amd_iommu_deactivate_guest_mode(void *data)
 	struct irq_cfg *cfg = ir_data->cfg;
 	u64 valid;
 
-	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
-	    !entry || !entry->lo.fields_vapic.guest_mode)
+	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
+		return -EINVAL;
+
+	if (!entry || !entry->lo.fields_vapic.guest_mode)
 		return 0;
 
 	valid = entry->lo.fields_remap.valid;