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

[Marc Zyngier]

On 2019-11-06 19:08, Michael Kelley wrote:
> From: Marc Zyngier <maz@xxxxxxxxxx>  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 ....

Hyper-V shipping with their own calling convention is fine by me. Linux
having to implement multiple calling conventions because the Hyper-V
folks refuse (for undisclosed reason) to adopt the standard isn't fine 
at
all.

HV can perfectly retain its interface for Windows or other things, but
please *at least* implement the standard interface on which all 
existing
operating systems rely.

Thanks,

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