linux-kernel - Re: [PATCH v3 1/5] arm64: make SCTLR2

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Message-ID: <aKYZNygBTVDurhDu@e129823.arm.com>
Date: Wed, 20 Aug 2025 19:51:35 +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,
	Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH v3 1/5] arm64: make SCTLR2_EL1 accessible

Hi Dave,

> > When the kernel runs at EL1, and yet is booted at EL2,
> > HCRX_EL2.SCTLR2En must be set to avoid trapping SCTLR2_EL1 accesses
> > from EL1 to EL2.
> >
> > Ensure this bit is set at the point of initialising EL2.
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> > Reviewed-by: Marc Zyngier <maz@...nel.org>
> > ---
> >  arch/arm64/include/asm/el2_setup.h | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
> > index 46033027510c..d755b4d46d77 100644
> > --- a/arch/arm64/include/asm/el2_setup.h
> > +++ b/arch/arm64/include/asm/el2_setup.h
> > @@ -57,9 +57,15 @@
> >          /* Enable GCS if supported */
> >  	mrs_s	x1, SYS_ID_AA64PFR1_EL1
> >  	ubfx	x1, x1, #ID_AA64PFR1_EL1_GCS_SHIFT, #4
> > -	cbz	x1, .Lset_hcrx_\@
> > +	cbz	x1, .Lskip_hcrx_GCSEn_\@
> >  	orr	x0, x0, #HCRX_EL2_GCSEn
> >
> > +.Lskip_hcrx_GCSEn_\@:
> > +	mrs_s	x1, SYS_ID_AA64MMFR3_EL1
> > +	ubfx	x1, x1, #ID_AA64MMFR3_EL1_SCTLRX_SHIFT, #4
> > +	cbz	x1, .Lset_hcrx_\@
> > +	orr	x0, x0, HCRX_EL2_SCTLR2En
>
> Nit: prefix immediate operands with # please -- see usage elsewhere in
> this file.
>
> (This comes from the legacy AArch32 syntax and has never been required
> by AArch64 assemblers, but it has become a tradition in the Linux arch
> code...)
>
> The only execptions to this rule are macros (mov_q, mrs_s etc. --
> frequently they have an underscore in the name; "real" instructions
> never do.)

Grr.. My fat finger.. Sorry to bother you.
I'll fix it and thanks for the great comment :)

>
> > +
> >  .Lset_hcrx_\@:
>
> Maybe rename this label to .Lskip_hcrx_SCTLR2En_\@, so that people
> don't have to keep renaming an existing label whenever they add
> another block here.

Okay. I'll change it.

Thanks!

--
Sincerely,
Yeoreum Yun