xen/arm: Cap the number of interrupt lines for dom0

Dom0 vGIC will use the same number of interrupt lines as the hardware GIC.
While the hardware GIC can support up to 1020 interrupt lines,
the vGIC is only supporting up to 992 interrupt lines.
This means that Xen will not be able to boot on platforms where the hardware
GIC supports more than 992 interrupt lines.
While it would make sense to increase the limits in the vGICs, this is not
trivial because of the design choices.
At the moment, only models seem to report the maximum of interrupt lines.
They also do not have any interrupt wired above the 992 limit.
So it should be fine to cap the number of interrupt lines for dom0 to 992 lines.

Signed-off-by: Lukas Juenger <juenger@ice.rwth-aachen.de>
Acked-by: Julien Grall <julien.grall@arm.com>

xen/arch/arm/setup.c

@@ -888,7 +888,13 @@ void __init start_xen(unsigned long boot_phys_offset,
     /* Create initial domain 0. */
     /* The vGIC for DOM0 is exactly emulating the hardware GIC */
     dom0_cfg.arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE;
-    dom0_cfg.arch.nr_spis = gic_number_lines() - 32;
+    /*
+     * Xen vGIC supports a maximum of 992 interrupt lines.
+     * 32 are substracted to cover local IRQs.
+     */
+    dom0_cfg.arch.nr_spis = min(gic_number_lines(), (unsigned int) 992) - 32;
+    if ( gic_number_lines() > 992 )
+        printk(XENLOG_WARNING "Maximum number of vGIC IRQs exceeded.\n");
     dom0_cfg.max_vcpus = dom0_max_vcpus();
 
     dom0 = domain_create(0, &dom0_cfg, true);