Re: [PATCH v3 4/9] KVM: PPC: Ultravisor: Add generic ultravisor call handler

Hi Paul,

On Mon, Jun 17, 2019 at 12:06:32PM +1000, Paul Mackerras wrote:

The thing we need to consider is that when SMFCTRL[E] = 0, a ucall
instruction becomes a hcall (that is, sc 2 is executed as if it was
sc 1).  In that case, the first argument to the ucall will be
interpreted as the hcall number.  Mostly that will happen not to be a
valid hcall number, but sometimes it might unavoidably be a valid but
unintended hcall number.

Shouldn't a caller of the ultravisor *know* that it is talking to the
ultravisor in the first place?  And not to the hypervisor.


Segher