Re: [Qemu-devel] [PATCH for-2.8 16/18] pc: add 'etc/boot-cpus' fw_cfg file for machine with more than 255 CPUs

[Michael S. Tsirkin]

On Fri, Aug 05, 2016 at 11:46:15AM +0200, Igor Mammedov wrote:
> Currently firmware uses 1 byte at 0x5F offset in RTC CMOS
> to get number of CPUs present at boot. However 1 byte is
> not enough to handle more than 255 CPUs.  So add a new
> fw_cfg file that would allow QEMU to tell it.
> For compat reasons add file only for machine types that
> support more than 255 CPUs.
> 
> Signed-off-by: Igor Mammedov <address@hidden>

Do we really need this? Why differentiate between boot
cpus and others? How about reusing the hotplug
register, such that it looks just as if all CPUs
were just added by hotplug?

> ---
>  hw/i386/pc.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index c2cd5bd..2b5581a 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1235,9 +1235,11 @@ void pc_machine_done(Notifier *notifier, void *data)
>      PCMachineState *pcms = container_of(notifier,
>                                          PCMachineState, machine_done);
>      PCIBus *bus = pcms->bus;
> +    static uint16_t boot_cpus;
>  
>      /* set the number of CPUs */
> -    rtc_set_memory(pcms->rtc, 0x5f, pc_present_cpus_count(pcms) - 1);
> +    boot_cpus = pc_present_cpus_count(pcms);
> +    rtc_set_memory(pcms->rtc, 0x5f, boot_cpus - 1);
>  
>      if (bus) {
>          int extra_hosts = 0;
> @@ -1258,8 +1260,16 @@ void pc_machine_done(Notifier *notifier, void *data)
>  
>      acpi_setup();
>      if (pcms->fw_cfg) {
> +        MachineClass *mc = MACHINE_GET_CLASS(pcms);
> +
>          pc_build_smbios(pcms->fw_cfg);
>          pc_build_feature_control_file(pcms);
> +
> +        if (mc->max_cpus > 255) {
> +            boot_cpus = cpu_to_le16(boot_cpus);
> +            fw_cfg_add_file(pcms->fw_cfg, "etc/boot-cpus", &boot_cpus,
> +                            sizeof(boot_cpus));
> +        }
>      }
>  }
>  
> -- 
> 2.7.4