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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-04-10 at 11:41 +0100, Marc Zyngier wrote:
> 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... ;-)

I hadn't noticed (or perhaps, remembered) that, thanks!

Ian.


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