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

[Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>]

Hi Julien,

On Mon, Apr 23, 2018 at 1:46 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> 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

Could you please clarify what you meant with "for everyone"? My
understanding is that you suggested this in
https://lists.xenproject.org/archives/html/xen-devel/2018-01/msg00979.html
Did something change meanwhile?

> 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.

Please clarify, I don't follow this.

>
> 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.
>

Could you please point me to a place where this is done on boot?

Thanks,
Mirela

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

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