Re: [PATCH 1/4] xen/arm: basic PSCI support, implement cpu_on

[Marc Zyngier <marc.zyngier@arm.com>]

On 09/04/13 14:57, Ian Campbell wrote:
> On Thu, 2013-03-21 at 18:42 +0000, Stefano Stabellini wrote:
>> Implement support for ARM Power State Coordination Interface, PSCI in
>> short. The current implementation is based on HVC and only supports the
>> cpu_on call.
> 
> Doesn't the PSCI interface require the use of SMC not HVC?

You can use both, and KVM uses HVC.

> I thought I heard Charles say at connect that there was now a PSCI v2,
> and I suspect I'm looking at the v1 document (which mentions HVC only in
> passing). Which interface did you implement?
> 
> Anyhow, we can trap SMCs to the hypervisor by setting the right control
> register bits. We should do this anyway -- no good can come of a guest
> making a call direct to the monitor!

Trapping guest access to Secure mode is always a good idea! ;-)

Unfortunately, there's a catch on ARMv8. If the CPU doesn't implement
secure mode, then SMC will UNDEF at the current exception level (not
trapping to EL2). Which means that for ARMv8, you basically have to
mandate HVC for PSCI at the HYP level...

	M.
-- 
Jazz is not dead. It just smells funny...