iommu/amd: Ensure GA log notifier callbacks finish running before module unload

Synchronize RCU when unregistering KVM's GA log notifier to ensure all
in-flight interrupt handlers complete before KVM-the module is unloaded.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20250315031048.2374109-1-seanjc@google.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: sean-jc

drivers/iommu/amd/iommu.c

@@ -982,6 +982,14 @@ int amd_iommu_register_ga_log_notifier(int (*notifier)(u32))
 {
 	iommu_ga_log_notifier = notifier;
 
+	/*
+	 * Ensure all in-flight IRQ handlers run to completion before returning
+	 * to the caller, e.g. to ensure module code isn't unloaded while it's
+	 * being executed in the IRQ handler.
+	 */
+	if (!notifier)
+		synchronize_rcu();
+
 	return 0;
 }
 EXPORT_SYMBOL(amd_iommu_register_ga_log_notifier);