linux-kernel - Re: [PATCH v3 4/5] arm64: initialise SCTLR2_EL1 at cpu_soft

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Message-ID: <aKbxbCNW8JNBEh/3@e129823.arm.com>
Date: Thu, 21 Aug 2025 11:14:04 +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,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, kvmarm@...ts.linux.dev
Subject: Re: [PATCH v3 4/5] arm64: initialise SCTLR2_EL1 at cpu_soft_restart()

Hi Dave,
> Hi,
>
> On Wed, Aug 13, 2025 at 01:01:17PM +0100, Yeoreum Yun wrote:
> > SCTLR2_EL1 register is optional starting from ARMv8.8/ARMv9.3,
> > and becomes mandatory from ARMv8.9/ARMv9.4
> > and serveral architectural feature are controled by bits in
> > these registers.
> >
> > Before, launching new kernel via kexec, initialise SCTLR2_EL1 explicitly.
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> > ---
> >  arch/arm64/kernel/cpu-reset.S | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/cpu-reset.S b/arch/arm64/kernel/cpu-reset.S
> > index c87445dde674..123564af345b 100644
> > --- a/arch/arm64/kernel/cpu-reset.S
> > +++ b/arch/arm64/kernel/cpu-reset.S
> > @@ -37,6 +37,12 @@ SYM_TYPED_FUNC_START(cpu_soft_restart)
> >  	 * regime if HCR_EL2.E2H == 1
> >  	 */
> >  	msr	sctlr_el1, x12
> > +
> > +alternative_if ARM64_HAS_SCTLR2
> > +	mov_q	x12, INIT_SCTLR2_EL1
> > +	msr_s	SYS_SCTLR2_EL1, x12
> > +alternative_else_nop_endif
> > +
>
> It would be better to do this based on the ID regs.
>
> Although the previous kernel _shouldn't_ have used SCTLR2 if the
> capability ARM64_HAS_SCTLR2 did not get enabled, it would be better to
> enforce a clean state here for the new kernel.
>
> If so, maybe one of the macros that you already defined can be used
> here?  (But it's also fine to open-code it.)

Ah got it. I'll change as your suggestion
Thanks!

[...]

--
Sincerely,
Yeoreum Yun