[PATCH v2] arm/arm64: KVM: detect CPU reset on CPU_PM_EXIT

[Christoffer Dall]

On Fri, Feb 21, 2014 at 11:46:56AM +0000, Marc Zyngier wrote:
> Commit 1fcf7ce0c602 (arm: kvm: implement CPU PM notifier) added
> support for CPU power-management, using a cpu_notifier to re-init
> KVM on a CPU that entered CPU idle.
> 
> The code assumed that a CPU entering idle would actually be powered
> off, loosing its state entierely, and would then need to be
> reinitialized. It turns out that this is not always the case, and
> some HW performs CPU PM without actually killing the core. In this
> case, we try to reinitialize KVM while it is still live. It ends up
> badly, as reported by Andre Przywara (using a Calxeda Midway):
> 
> [    3.663897] Kernel panic - not syncing: unexpected prefetch abort in Hyp mode at: 0x685760
> [    3.663897] unexpected data abort in Hyp mode at: 0xc067d150
> [    3.663897] unexpected HVC/SVC trap in Hyp mode at: 0xc0901dd0
> 
> The trick here is to detect if we've been through a full re-init or
> not by looking at HVBAR (VBAR_EL2 on arm64). This involves
> implementing the backend for __hyp_get_vectors in the main KVM HYP
> code (rather small), and checking the return value against the
> default one when the CPU notifier is called on CPU_PM_EXIT.
> 
> Reported-by: Andre Przywara <osp at andrep.de>
> Tested-by: Andre Przywara <osp at andrep.de>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> Cc: Rob Herring <rob.herring at linaro.org>
> Acked-by: Christoffer Dall <christoffer.dall at linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>

Thanks!

Looks good.

-Christoffer