linux-kernel - Re: [PATCH v4 0/5] initialize SCTRL2

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Message-ID: <aL68enBTkmsjJGPy@e129823.arm.com>
Date: Mon, 8 Sep 2025 12:22:34 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Dave Martin <Dave.Martin@....com>
Cc: catalin.marinas@....com, will@...nel.org, broonie@...nel.org,
	oliver.upton@...ux.dev, anshuman.khandual@....com, robh@...nel.org,
	james.morse@....com, mark.rutland@....com, joey.gouly@....com,
	ahmed.genidi@....com, kevin.brodsky@....com,
	scott@...amperecomputing.com, mbenes@...e.cz,
	james.clark@...aro.org, frederic@...nel.org, rafael@...nel.org,
	pavel@...nel.org, ryan.roberts@....com, suzuki.poulose@....com,
	maz@...nel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	kvmarm@...ts.linux.dev
Subject: Re: [PATCH v4 0/5] initialize SCTRL2_ELx

Hi,

> [...]
>
> > > > > Have you tested all the code paths, or are there some things that have
> > > > > not been tested?
> > > >
> > > > I've tested for pKVM, nested and nhve and crash path
> > > > (I do my best what can I do for modified path).
> > >
> > > Was that just confirming that the kernel boots / does not crash?
> >
> > Not only that, since the my last mistake, I've check it with debugger
> > too -- set the SCTLR2_ELx as I expected.
> >
> > >
> > > What about CPU suspend/resume and hotplug?
> >
> > Of course It's done both enter/exit idle and hotplug with related kselftest test.
>
> Were you able to step through these paths, too?

Yes. with debugger and some trick with:
  asm volatile("b ." ::: "memory");

checking a cpu idle (by not loading any work) without any load and
checking cpu-hotplug with kselftest's cpu-on-off-test.sh.

So, by hitting the "b .", I've stepped in and confirm the SCTLR2_ELx set
as it intended.

>
> > > My concern is that most of the defined SCTLR2_ELx bits won't affect
> > > kernel execution unless the corresponding hardware features are
> > > actively being used -- so while we know that the patches don't break
> > > the kernel, this may not prove that SCTLR2_ELx is really being
> > > initialised / saved / restored / reset correctly.
> >
> > That's why I've confirmed with debugger whether the SCTLR2_ELx value
> > sets as I expected... personally I've done as much as I can for
> > test related for SCTLR2_ELx.
>
> OK
>
> > > > > Since this code is not useful by itself, it may make sense to delay
> > > > > merging it until we have patches for a feature that depends on SCTLR2.
> > > >
> > > > Whatever I pass this detiermination for maintainer.
> > >
> > > Sure, that's just my opinion.
> > >
> > > Either way, this doesn't stop anyone from building support for specific
> > > features on top of this series before it gets merged.
>
>
> Looking again through this series, I realised that the requirements for
> this feature are not documented in booting.rst.
>
> Does the following patch look good to you?  If so, feel free to append
> it to the series (with your Reviewed-by, if you're happy with the
> changes).
>
> It's probably worth double-checking the bit numbers etc.  I wrote this
> some weeks ago and then forgot about it.

I've missed this and Thanks for your efforts.
The bits you documented have no problem as far as I checked.
Let me include this too in next series.

(I'm still checking your suggestion to use .ifc. as soon as finish
this. I'll repost it according to your suggestion)


Thanks!

[...]

--
Sincerely,
Yeoreum Yun