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

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

On 10/04/13 11:13, Ian Campbell wrote:
> On Tue, 2013-04-09 at 15:23 +0100, Marc Zyngier wrote:
>> 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.
> 
> It makes good sense for Xen to follow suit then I think.
> 
>>> 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...
> 
> That pretty much seals it then!
> 
> Do I infer that on v7 SMC w/o security extensions will trap?

ARMv7 mandates security extensions if you have virtualization
extensions, so this is a moot point... ;-)

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