linux-kernel - Re: [PATCH v2 2/6] arm64: initialise SCTLR2

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Message-ID: <86pld190l2.wl-maz@kernel.org>
Date: Mon, 11 Aug 2025 19:26:17 +0100
From: Marc Zyngier <maz@...nel.org>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: catalin.marinas@....com,
	will@...nel.org,
	broonie@...nel.org,
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	linux-arm-kernel@...ts.infradead.org,
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Subject: Re: [PATCH v2 2/6] arm64: initialise SCTLR2_ELx register at boot time

[dropping ry111@...111.site, which bounces]

On Mon, 11 Aug 2025 17:33:36 +0100,
Yeoreum Yun <yeoreum.yun@....com> wrote:
> 
> add initialisation for SCTRL2_ELx register at boot time.

Again, please expand.

> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> ---
>  arch/arm64/include/asm/el2_setup.h |  6 ++++++
>  arch/arm64/include/asm/sysreg.h    | 22 ++++++++++++++++++++++
>  arch/arm64/kernel/head.S           |  5 ++++-
>  3 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
> index d755b4d46d77..347ac4cc1283 100644
> --- a/arch/arm64/include/asm/el2_setup.h
> +++ b/arch/arm64/include/asm/el2_setup.h
> @@ -48,6 +48,11 @@
>  	isb
>  .endm
>  
> +.macro __init_el2_sctlr2

Writing this as __init_sctlr2_el2 would read vastly better (yes, I
know most macros in this file are similarly braindead).

> +	init_sctlr2_elx	2, x0
> +	isb
> +.endm
> +
>  .macro __init_el2_hcrx
>  	mrs	x0, id_aa64mmfr1_el1
>  	ubfx	x0, x0, #ID_AA64MMFR1_EL1_HCX_SHIFT, #4
> @@ -411,6 +416,7 @@
>   */
>  .macro init_el2_state
>  	__init_el2_sctlr
> +	__init_el2_sctlr2
>  	__init_el2_hcrx
>  	__init_el2_timers
>  	__init_el2_debug
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index d5b5f2ae1afa..8b82af5be199 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -868,6 +868,8 @@
>  #define INIT_SCTLR_EL2_MMU_OFF \
>  	(SCTLR_EL2_RES1 | ENDIAN_SET_EL2)
>  
> +#define INIT_SCTLR2_EL2			UL(0)
> +
>  /* SCTLR_EL1 specific flags. */
>  #ifdef CONFIG_CPU_BIG_ENDIAN
>  #define ENDIAN_SET_EL1		(SCTLR_EL1_E0E | SCTLR_ELx_EE)
> @@ -888,6 +890,8 @@
>  	 SCTLR_EL1_LSMAOE | SCTLR_EL1_nTLSMD | SCTLR_EL1_EIS   | \
>  	 SCTLR_EL1_TSCXT  | SCTLR_EL1_EOS)
>  
> +#define INIT_SCTLR2_EL1			UL(0)
> +
>  /* MAIR_ELx memory attributes (used by Linux) */
>  #define MAIR_ATTR_DEVICE_nGnRnE		UL(0x00)
>  #define MAIR_ATTR_DEVICE_nGnRE		UL(0x04)
> @@ -1164,6 +1168,24 @@
>  	msr	hcr_el2, \reg
>  #endif
>  	.endm
> +
> +	.macro init_sctlr2_elx, el, tmp
> +	mrs_s	\tmp, SYS_ID_AA64MMFR3_EL1
> +	ubfx	\tmp, \tmp, #ID_AA64MMFR3_EL1_SCTLRX_SHIFT, #4
> +	cbz	\tmp, .Lskip_sctlr2_\@
> +	.if	\el == 2
> +	mov_q	\tmp, INIT_SCTLR2_EL2
> +	msr_s	SYS_SCTLR_EL2, \tmp
> +	.else
> +	mov_q	\tmp, INIT_SCTLR2_EL1
> +	.if	\el == 12
> +	msr_s	SYS_SCTLR_EL12, \tmp
> +	.else
> +	msr_s	SYS_SCTLR_EL1, \tmp
> +	.endif

I don't think this is the correct place for this macro.
asm/assembler.h seems more suitable, and already has that sort of
things.

> +	.endif
> +.Lskip_sctlr2_\@:
> +	.endm
>  #else
>  
>  #include <linux/bitfield.h>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index ca04b338cb0d..0dff7593e50b 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -276,6 +276,7 @@ SYM_INNER_LABEL(init_el1, SYM_L_LOCAL)
>  	mov_q	x0, INIT_SCTLR_EL1_MMU_OFF
>  	pre_disable_mmu_workaround
>  	msr	sctlr_el1, x0
> +	init_sctlr2_elx	1, x0
>  	isb
>  	mov_q	x0, INIT_PSTATE_EL1
>  	msr	spsr_el1, x0
> @@ -298,7 +299,6 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
>  	msr	sctlr_el2, x0
>  	isb
>  0:
> -
>  	init_el2_hcr	HCR_HOST_NVHE_FLAGS
>  	init_el2_state
>  
> @@ -315,12 +315,15 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
>  
>  	/* Set a sane SCTLR_EL1, the VHE way */
>  	msr_s	SYS_SCTLR_EL12, x1
> +	init_sctlr2_elx	12, x2
>  	mov	x2, #BOOT_CPU_FLAG_E2H
>  	b	3f
>  
>  2:
>  	msr	sctlr_el1, x1
> +	init_sctlr2_elx	1, x2
>  	mov	x2, xzr
> +
>  3:
>  	mov	x0, #INIT_PSTATE_EL1
>  	msr	spsr_el2, x0

This is missing something: you should resynchronise SCTLR2_EL2 from
SCTLR2_EL1 in __finalise_el2, rather than relying on whatever you've
set in __init_el2_sctlr2.

	M.

-- 
Without deviation from the norm, progress is not possible.