Hi Christophe,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on xen-tip/linux-next]
[also build test ERROR on v4.19 next-20181019]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Christophe-Leroy/idle-x86-remove-the-call-to-boot_init_stack_canary-from-cpu_startup_entry/20181020-061217
base:   https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git linux-next
config: x86_64-rhel (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   arch/x86/xen/smp_pv.c: In function 'cpu_bringup_and_idle':
>> arch/x86/xen/smp_pv.c:91:2: error: implicit declaration of function 'boot_init_stack_canary'; did you mean 'snprint_stack_trace'? [-Werror=implicit-function-declaration]
     boot_init_stack_canary();
     ^~~~~~~~~~~~~~~~~~~~~~
     snprint_stack_trace
   cc1: some warnings being treated as errors

vim +91 arch/x86/xen/smp_pv.c

    87	
    88	asmlinkage __visible void cpu_bringup_and_idle(void)
    89	{
    90		cpu_bringup();
  > 91		boot_init_stack_canary();
    92		cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
    93	}
    94	

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