xen/arm: Restrict when a physical IRQ can be routed/removed from/to a domain

Xen is currently allowing to route/remove an interrupt from/to the
domain while it is running.

However, we never sync the virtual interrupt state to the physical
interrupt. This could lead to undesirable effect on the vGIC emulation
and potentially the hardware.

One solution would be to sync the interrupt state when routing, but I am
not sure it is worth the effort as you never really when it is safe to
route/remove the interrupt when a domain is running.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/gic.c

@@ -136,6 +136,14 @@ int gic_route_irq_to_guest(struct domain *d, unsigned int virq,
     ASSERT(virq < vgic_num_irqs(d));
     ASSERT(!is_lpi(virq));
 
+    /*
+     * When routing an IRQ to guest, the virtual state is not synced
+     * back to the physical IRQ. To prevent get unsync, restrict the
+     * routing to when the Domain is been created.
+     */
+    if ( d->creation_finished )
+        return -EBUSY;
+
     ret = vgic_connect_hw_irq(d, NULL, virq, desc, true);
     if ( ret )
         return ret;
@@ -160,25 +168,19 @@ int gic_remove_irq_from_guest(struct domain *d, unsigned int virq,
     ASSERT(test_bit(_IRQ_GUEST, &desc->status));
     ASSERT(!is_lpi(virq));
 
-    if ( d->is_dying )
-    {
-        desc->handler->shutdown(desc);
+    /*
+     * Removing an interrupt while the domain is running may have
+     * undesirable effect on the vGIC emulation.
+     */
+    if ( !d->is_dying )
+        return -EBUSY;
 
-        /* EOI the IRQ if it has not been done by the guest */
-        if ( test_bit(_IRQ_INPROGRESS, &desc->status) )
-            gic_hw_ops->deactivate_irq(desc);
-        clear_bit(_IRQ_INPROGRESS, &desc->status);
-    }
-    else
-    {
-        /*
-         * TODO: Handle eviction from LRs For now, deny
-         * remove if the IRQ is inflight or not disabled.
-         */
-        if ( test_bit(_IRQ_INPROGRESS, &desc->status) ||
-             !test_bit(_IRQ_DISABLED, &desc->status) )
-            return -EBUSY;
-    }
+    desc->handler->shutdown(desc);
+
+    /* EOI the IRQ if it has not been done by the guest */
+    if ( test_bit(_IRQ_INPROGRESS, &desc->status) )
+        gic_hw_ops->deactivate_irq(desc);
+    clear_bit(_IRQ_INPROGRESS, &desc->status);
 
     ret = vgic_connect_hw_irq(d, NULL, virq, desc, false);
     if ( ret )