Re: [PATCH v5 0/5] arm64: Fix behavior of maxcpus=n

From: Will Deacon
Date: Tue Apr 26 2016 - 10:50:51 EST


On Tue, Apr 26, 2016 at 03:48:55PM +0100, Suzuki K Poulose wrote:
> This series is an attempt at fixing the maxcpus=n behavior
> on arm64. So far we have disabled hotplugging a CPU > n,
> when maxcpus=n is in effect, due to following reasons.
>
> 1) Possible cpu feature incompatibilities with the new CPU
> in heterogeneous systems.
> 2) New CPU requiring an errata work around which was not detected
> (and the code patched in) at boot time.
> 3) Failure to initialise the PMU in case the supported CPUs are
> not online while probing the PMU.
>
> (1) has been mostly solved with our early CPU feature verification
> support. This series tries to address (2) & (3).
>
> (2) is solved by iterating over the known erratas and checking if
> the new CPU requires an errata not set in the cpu_hwcaps, failing
> which, we kill the CPU. We plan to fix this properly by retaining
> the CPU errata work arounds and apply the required at runtime.
>
> (3) is ignored and will not be fixed as there is no reliable way of
> knowing if there would be a CPU that will be online to support the
> PMU.
>
> In the process, also restores the capability to check GIC interface settings
> by the firmware on individual CPUs.
>
> Tested on Juno with maxcpus=2 (enables A57 cores and A57-PMU) and
> maxcpus=1 (disables both A57 cores and A57-PMU).
>
> This series applies on aarch64/for-next/core :
>
> The tree is available here :
> git://linux-arm.org/linux-skp.git maxcpus/v5
>
> Changes since V4:
> - Address Catalin's comments
> - Rebased to aarch64 for-next/core
> - Add Reviewed/Acked bys.

I merged this yesterday onto for-next/core. Please can you check that
I fixed everything up that you expected?

Will