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

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Message-ID: <aLgvzKeEPn325aRO@e129823.arm.com>
Date: Wed, 3 Sep 2025 13:08:44 +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 Dave,

[...]
> > > > This series introduces initial support for the SCTLR2_ELx registers in Linux.
> > > > The feature is optional starting from ARMv8.8/ARMv9.3,
> > > > and becomes mandatory from ARMv8.9/ARMv9.4.
> > > >
> > > > Currently, Linux has no strict need to modify SCTLR2_ELx--
> > > > at least assuming that firmware initializes
> > > > these registers to reasonable defaults.
> > > >
> > > > However, several upcoming architectural features will require configuring
> > > > control bits in these registers.
> > > > Notable examples include FEAT_PAuth_LR and FEAT_CPA2.
> > >
> > > This looks OK to me now, except for one or two minor issues (see
> > > replies to the patches).
> > >
> > > I think we will need a way of testing all the code paths before this
> > > should be merged, though.
> > >
> > > 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.

>
> 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.
>
> > > 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.

Okay.

Thanks!

--
Sincerely,
Yeoreum Yun