[PATCH 0/2] PSCI: don't call CPU_OFF when it might fail

[Stefano Stabellini]

On Fri, 5 Sep 2014, Mark Rutland wrote:
> [Apologies to all who received this already, I typo'd the LAKML address]
> 
> In certain conditions PSCI's CPU_OFF call may return DENIED (in the presence of
> a UP OS on the secure world), or might not exist (in early implementations
> prior to PSCI 0.2). Both the arm and arm64 callers fail to handle the former,
> and the arm caller doesn't handle the latter.
> 
> We can determine wether a CPU_OFF call will succeed by calling
> MIGRATE_INFO_TYPE. If we receive 2 (A.K.A. PSCI_0_2_TOS_MP) in response we know
> that CPU_OFF should succeed, and in other cases it is necessary to discover
> which CPU said OS lives on and attempt migration. As there don't seem to be any
> UP implementations out there so far, for now we can limit ourselves to only
> supporting CPU hotplug in the PSCI_0_2_TOS_MP case. Hotplug support on such
> systems will require additional work, but at least they won't blow up by
> default.
> 
> These patches add the necessary checks to the arm and arm64 PSCI callers to
> prevent the issues described above. MIGRATE_INFO_TYPE is a mandatory part of
> PSCI 0.2, so no conforming implementation should be adversely affected. Both
> the ARM Trusted Firmware and KVM respond to MIGRATE_INFO_TYPE with
> PSCI_0_2_TOS_MP, so should see no loss of functionality (verified on Juno). 
> 
> Thanks,
> Mark.
> 
> Mark Rutland (2):
>   arm64: psci: respect MIGRATE_INFO_TYPE
>   arm: psci: don't call CPU_OFF blindly
> 
>  arch/arm/kernel/psci_smp.c | 36 +++++++++++++++++++++++++++++-------
>  arch/arm64/kernel/psci.c   | 14 ++++++++++++++
>  2 files changed, 43 insertions(+), 7 deletions(-)
 
The patches look good to me and AFACT they would work fine on Xen 4.4
and the soon to be release 4.5.