Re: [PATCH v4 13/17] arm64: preserve x18 when CPU is suspended

Nick Desaulniers
2019-11-04T22:00:07Z

On Mon, Nov 4, 2019 at 1:38 PM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> On Mon, Nov 4, 2019 at 5:20 AM Marc Zyngier <maz@kernel.org> wrote:
> > > ENTRY(cpu_do_suspend)
> > > mrs x2, tpidr_el0
> > > @@ -73,6 +75,9 @@ alternative_endif
> > > stp x8, x9, [x0, #48]
> > > stp x10, x11, [x0, #64]
> > > stp x12, x13, [x0, #80]
> > > +#ifdef CONFIG_SHADOW_CALL_STACK
> > > + str x18, [x0, #96]
> > > +#endif
> >
> > Do we need the #ifdefery here? We didn't add that to the KVM path,
> > and I'd feel better having a single behaviour, specially when
> > NR_CTX_REGS is unconditionally sized to hold 13 regs.
>
> I'm fine with dropping the ifdefs here in v5 unless someone objects to this.

Oh, yeah I guess it would be good to be consistent. Rather than drop
the ifdefs, would you (Marc) be ok with conditionally setting
NR_CTX_REGS based on CONFIG_SHADOW_CALL_STACK, and doing so in KVM?
(So 3 ifdefs, rather than 0)?

Without any conditionals or comments, it's not clear why x18 is being
saved and restored (unless git blame survives, or a comment is added
in place of the ifdefs in v6).
--
Thanks,
~Nick Desaulniers