[PATCH v5 2/8] arm64: hyperv: Add hypercall and register access functions

[Michael Kelley]

From: Marc Zyngier <maz at kernel.org>  Sent: Wednesday, November 6, 2019 2:20 AM
> 
> On 2019-10-03 20:12, Michael Kelley wrote:
> > Add ARM64-specific code to make Hyper-V hypercalls and to
> > access virtual processor synthetic registers via hypercalls.
> > Hypercalls use a Hyper-V specific calling sequence with a non-zero
> > immediate value per Section 2.9 of the SMC Calling Convention
> > spec.
> 
> I find this "following the spec by actively sidestepping it" counter
> productive. You (or rather the Hyper-V people) are reinventing the
> wheel (of the slightly square variety) instead of using the standard
> that the whole of the ARM ecosystem seems happy to take advantage
> of.
> 
> I wonder what is the rational for this. If something doesn't quite
> work for Hyper-V, I think we'd all like to know.
> 

I'll go another round internally with the Hyper-V people on this
topic and impress upon them the desire of the Linux community to
have Hyper-V adopt the true spirit of the spec.  But I know they are
fairly set in their approach at this point, regardless of the technical
merits or lack thereof.  Hyper-V is shipping and in use as a commercial
product on ARM64 hardware, which makes it harder to change.  I
hope we can find a way to avoid a complete impasse ....

Michael