From: "Edgar E. Iglesias" <edgar.iglesias@amd.com>

Add SMP support for Xen PVH ARM guests.
Create ms->smp.max_cpus ioreq servers to handle hotplug.

Note that ms->smp.max_cpus will be passed to us by the
user (Xen tools) set to the guests maxvcpus.

The value in mc->max_cpus is an absolute maximum for the
-smp option and won't be used to setup ioreq servers unless
the user explicitly specifies it with -smp.

If the user doesn't pass -smp on the command-line, smp.cpus
and smp.max_cpus will default to 1.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---
 hw/arm/xen_arm.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/hw/arm/xen_arm.c b/hw/arm/xen_arm.c
index 5f75cc3779..fda65d0d8d 100644
--- a/hw/arm/xen_arm.c
+++ b/hw/arm/xen_arm.c
@@ -173,7 +173,7 @@ static void xen_arm_init(MachineState *machine)
 
     xen_init_ram(machine);
 
-    xen_register_ioreq(xam->state, machine->smp.cpus, &xen_memory_listener);
+    xen_register_ioreq(xam->state, machine->smp.max_cpus, &xen_memory_listener);
 
     xen_create_virtio_mmio_devices(xam);
 
@@ -218,7 +218,26 @@ static void xen_arm_machine_class_init(ObjectClass *oc, void *data)
     MachineClass *mc = MACHINE_CLASS(oc);
     mc->desc = "Xen PVH ARM machine";
     mc->init = xen_arm_init;
-    mc->max_cpus = 1;
+
+    /*
+     * mc->max_cpus holds the MAX value allowed in the -smp command-line opts.
+     *
+     * 1. If users don't pass any -smp option:
+     *   ms->smp.cpus will default to 1.
+     *   ms->smp.max_cpus will default to 1.
+     *
+     * 2. If users pass -smp X:
+     *   ms->smp.cpus will be set to X.
+     *   ms->smp.max_cpus will also be set to X.
+     *
+     * 3. If users pass -smp X,maxcpus=Y:
+     *   ms->smp.cpus will be set to X.
+     *   ms->smp.max_cpus will be set to Y.
+     *
+     * In scenarios 2 and 3, if X or Y are set to something larger than
+     * mc->max_cpus, QEMU will bail out with an error message.
+     */
+    mc->max_cpus = GUEST_MAX_VCPUS;
     mc->default_machine_opts = "accel=xen";
     /* Set explicitly here to make sure that real ram_size is passed */
     mc->default_ram_size = 0;
-- 
2.43.0