Re: [Xen-devel] [PATCH v2 10/10] xen/arm: Call check_local_cpu_errata for secondary CPU only on boot

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 20/04/18 13:25, Mirela Simonovic wrote:
> Checking CPU errata should be done only when a CPU is initially booted.
> It is assumed that the CPU which is hotplugged after the system/Xen boots,
> was initially hotplugged during the system/Xen boot, so errata is checked
> by each CPU only once, on boot.
It is a good idea to document the assumption in the code. This will help 
to know what is missing for other use case.
> Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>
>
> ---
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> ---
>   xen/arch/arm/smpboot.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
> index d01b51592d..5d6c6cadec 100644
> --- a/xen/arch/arm/smpboot.c
> +++ b/xen/arch/arm/smpboot.c
> @@ -366,8 +366,8 @@ void start_secondary(unsigned long boot_phys_offset,
>   
>       if ( system_state != SYS_STATE_boot )
>           setup_virt_paging_secondary();
> -
> -    check_local_cpu_errata();
> +    else
> +        check_local_cpu_errata();
No, check_local_cpu_errata should be called for everyone. This check 
should be moved in the function with a TODO explaining what needs to be 
done. Likely this will be go over the CPU errata and see if there are 
any issue with the one currently selected.
Also, I just realized that any "cpu capability" (e.g spectre workaround) 
 that requires to be enabled will not be done on hotplugged CPU. You 
likely need to implement a version of enable_errata_workaround for them.
Cheers,

>   
>       printk(XENLOG_DEBUG "CPU %u booted.\n", smp_processor_id());
>   
--
Julien Grall

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