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

[mark.rutland@arm.com (Mark Rutland)]

On Fri, Sep 05, 2014 at 09:53:05PM +0100, Stefano Stabellini wrote:
> 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.

Cheers.

Can I take that as an ack?

Mark.