[RFC PATCH 2/5] ARM/ARM64: KVM: Forward PSCI SYSTEM_OFF and SYSTEM_RESET to user space

[Christoffer Dall]

On Thu, Oct 17, 2013 at 04:43:59PM +0530, Anup Patel wrote:
> On Thu, Oct 17, 2013 at 2:07 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
> > On 16/10/13 18:02, Anup Patel wrote:
> >> The PSCI SYSTEM_OFF and SYSTEM_RESET functions are VM or Guest level
> >> functions hence cannot be emulated by the in-kernel PSCI emulation code.
> >
> > Why can't we implement system-wide functionality in the kernel? I fail
> > to see the issue here.
> >
> >> To tackle this, we forward PSCI SYSTEM_OFF and SYSTEM_RESET function
> >> calls from Guest to user space (i.e. QEMU or KVMTOOL) via KVM run
> >> structure with KVM_EXIT_PSCI exit reason.
> >
> > I'm really not keen on this approach. Having part of the PSCI
> > implementation offloaded to userspace means we don't have a complete
> > implementation in KVM anymore, and we end-up duplicating functionality
> > all over the place.
> >
> > Also, OFF and RESET are not PSCI specific concepts, and could be
> > implemented in various ways. I'm more inclined to return a
> > *standardized* exit code that the various platforms can interpret.
> 
> Please refer to the documentation of SYSTEM_OFF and SYSTEM_RESET
> functions in the PSCI specifications.
> (More preciesly section 5.10 and 5.11 of
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0022b/index.html)
> 
Anup,

I think everyone knows where to find the specs, and I'm even more sure
that Marc knows the details of PSCI.

If there is a certain aspect of the spec that you find helpful to this
discussion that supports an implementation or design decision, I suggest
you try more carefully to explain why you think it is the right
solution, possibly using references to the specs in order to help people
out.

-Christoffer