linux-kernel - Re: [PATCH v3 0/5] initialize SCTRL2

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Message-ID: <aKXlvcqM90197MiJ@e133380.arm.com>
Date: Wed, 20 Aug 2025 16:11:57 +0100
From: Dave Martin <Dave.Martin@....com>
To: Yeoreum Yun <yeoreum.yun@....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,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, kvmarm@...ts.linux.dev
Subject: Re: [PATCH v3 0/5] initialize SCTRL2_ELx

Hi,

On Wed, Aug 13, 2025 at 01:01:13PM +0100, Yeoreum Yun wrote:
> 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 overall to me, apart from some confusion between
SCTLR_ELx and SCTLR2_ELx in patch 2 (see my comments there).

This code will need to be tested somehow.  Do you have any thoughts on
this?  Hacking the bootwrapper, KVM and/or kvmtool may provide a way of
checking what happens when the kernel is entered with "wrong" initial
values in relevant bits (HRCX_EL2.SCTLR2En, SCTLR2_EL{1,2}).

Regarding the patch history:

> Patch History
> ==============
> from v2 to v3:
>   - rewrite commit messages.
>   - fix missing SCTLR2_EL2 synchonization at boot.
>   - https://lore.kernel.org/all/20250811163340.1561893-1-yeoreum.yun@arm.com/
> 
> from v1 to v2:
>   - rebase to v6.17-rc1
>   - https://lore.kernel.org/all/20250804121724.3681531-1-yeoreum.yun@arm.com/

Going forwards, can you try to make sure that significant changes to
the series are all mentioned here?

I didn't have time to look at v2, and in the meantime half of the
series disappeared and a chunk of code was moved from one patch to
another.  I saves reviewers some time and effort if they do not have to
dig through previous review conversations in order to understand what
changed between versions of a series.

(No need to mention every trivial change, though.)

Cheers
---Dave