Re: [Xen-devel] [PATCH v2 6/6] xen/arm: update the docs about heterogeneous computing

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 19/02/18 21:58, Stefano Stabellini wrote:
> diff --git a/docs/misc/xen-command-line.markdown 
> b/docs/misc/xen-command-line.markdown
> index 2184cb9..8997904 100644
> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -1007,7 +1007,12 @@ Control Xens use of the APEI Hardware Error Source 
> Table, should one be found.
>   
>   Say yes at your own risk if you want to enable heterogenous computing
>   (such as big.LITTLE). This may result to an unstable and insecure
> -platform. When the option is disabled (default), CPUs that are not
> +platform, unless you manually specify the cpu affinity of all domains so
> +that all vcpus are scheduled on the same class of pcpus (big or LITTLE
> +but not both). vcpu migration between big cores and LITTLE cores is not
> +supported. See docs/misc/arm/big.LITTLE.txt for more information.
> +
> +When the hmp-unsafe option is disabled (default), CPUs that are not
>   identical to the boot CPU will be parked and not used by Xen.
>   
>   ### hpetbroadcast
> diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
> index 122c0b5..d04b7c7 100644
> --- a/xen/arch/arm/smpboot.c
> +++ b/xen/arch/arm/smpboot.c
> @@ -266,7 +266,7 @@ void __init smp_init_cpus(void)
>   
>       if ( opt_hmp_unsafe )
>           warning_add("WARNING: HMP COMPUTING HAS BEEN ENABLED.\n"
> -                    "It has implications on the security and stability of the 
> system.\n");
> +                    "It has implications on the security and stability of the 
> system, unless the cpu affinity of all domains is specified.\n");
The warning message will not be print nicely on serial. Please make sure 
it is split at 72 characters.
>   }
>   
>   int __init
> @@ -308,13 +308,14 @@ void start_secondary(unsigned long boot_phys_offset,
>       /*
>        * Currently Xen assumes the platform has only one kind of CPUs.
>        * This assumption does not hold on big.LITTLE platform and may
> -     * result to instability and insecure platform. Better to park them
> -     * for now.
> +     * result to instability and insecure platform (unless cpu affinity
> +     * is manually specified for all domains). Better to park them for
> +     * now.
>        */
>       if ( !opt_hmp_unsafe &&
>            current_cpu_data.midr.bits != boot_cpu_data.midr.bits )
>       {
> -        printk(XENLOG_ERR "CPU%u MIDR (0x%x) does not match boot CPU MIDR 
> (0x%x).\n",
> +        printk(XENLOG_ERR "CPU%u MIDR (0x%x) does not match boot CPU MIDR (0x%x), 
> disable cpu (see big.LITTLE.txt under docs/).\n",
Same here.

>                  smp_processor_id(), current_cpu_data.midr.bits,
>                  boot_cpu_data.midr.bits);
>           stop_cpu();
Cheers,

--
Julien Grall

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