Subject: ARM64: CPU Hotplug: can't enable more cpus than maxcpus value (kernel 4.5)

From: [email-masked] (Suzuki K. Poulose)
Date: Thu, 3 Mar 2016 14:59:29 +0000

On 03/03/16 14:42, Mark Rutland wrote:

>> However for arm64 it is implemented that cpu_present_mask is
>> explicetely set accordingly to 'maxcpus' value. Is it design intent ?
>
> To some extent, yes.
>
> Due to the possibility of a heterogeneous system, we must bring all CPUs
> online at boot time, and cannot defer this.
>
> This is necessary to detect the common subset of supported features, and
> also to detect the full set of CPUs in the system to correctly apply
> errata workarounds which require kernel text patching.

We don't have this limitation anymore, as we can check if the booting CPU
has any conflicting/missing features w.r.t the established set and fail the
booting if it does.

Cheers
Suzuki