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

[Igor Mammedov]

On Thu, 20 Oct 2016 16:51:48 -0200
Eduardo Habkost <address@hidden> wrote:

> On Thu, Oct 20, 2016 at 04:58:42PM +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>  
> 
> I suggest squashing this into the patch, to clarify why we are
> setting it to 0.
> 
> Signed-off-by: Eduardo Habkost <address@hidden>

Could you squash it in while merging series?

> ---
>  hw/i386/pc.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index c6f6747..a03b384 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1225,6 +1225,10 @@ static void 
> pc_build_feature_control_file(PCMachineState *pcms)
>  static void rtc_set_cpus_count(ISADevice *rtc, uint16_t cpus_count)
>  {
>      if (cpus_count > 0xff) {
> +        /* If the number of CPUs can't be represented in 8 bits, the
> +         * BIOS must use "etc/boot-cpus". Set RTC field to 0 just
> +         * to make old BIOSes fail more predictably.
> +         */
>          rtc_set_memory(rtc, 0x5f, 0);
>      } else {
>          rtc_set_memory(rtc, 0x5f, cpus_count - 1);