KVM: PPC: Book3S HV: XIVE: Clear file mapping when device is released

Improve the release of the XIVE KVM device by clearing the file
address_space, which is used to unmap the interrupt ESB pages when a
device is passed-through.
Suggested-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_xive_native.c

@@ -976,6 +976,14 @@ static void kvmppc_xive_native_release(struct kvm_device *dev)
 
 	pr_devel("Releasing xive native device\n");
 
+	/*
+	 * Clear the KVM device file address_space which is used to
+	 * unmap the ESB pages when a device is passed-through.
+	 */
+	mutex_lock(&xive->mapping_lock);
+	xive->mapping = NULL;
+	mutex_unlock(&xive->mapping_lock);
+
 	/*
 	 * Since this is the device release function, we know that
 	 * userspace does not have any open fd or mmap referring to