Re: [PATCH v1 04/10] hw/arm: xenpvh: Add support for SMP guests

[Stefano Stabellini]

On Mon, 12 Aug 2024, Edgar E. Iglesias wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias@amd.com>
> 
> Add SMP support for Xen PVH ARM guests. Create max_cpus ioreq
> servers to handle hotplug.
> 
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
> ---
>  hw/arm/xen_arm.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/arm/xen_arm.c b/hw/arm/xen_arm.c
> index 5f75cc3779..ef8315969c 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 +218,8 @@ 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;
> +    /* MAX number of vcpus supported by Xen.  */
> +    mc->max_cpus = GUEST_MAX_VCPUS;

Will this cause allocations of data structures with 128 elements?
Looking at hw/xen/xen-hvm-common.c:xen_do_ioreq_register it seems
possible? Or hw/xen/xen-hvm-common.c:xen_do_ioreq_register is called
later on with the precise vCPU value which should be provided to QEMU
via the -smp command line option
(tools/libs/light/libxl_dm.c:libxl__build_device_model_args_new)?