linux-kernel - Re: [PATCH v2] arm64: fix cleared E0POE bit after cpu

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Message-ID: <846e1998-b508-4433-9db6-3a52ff23552f@arm.com>
Date: Wed, 7 Jan 2026 17:54:09 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Yeoreum Yun <yeoreum.yun@....com>, linux-pm@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: rafael@...nel.org, pavel@...nel.org, catalin.marinas@....com,
 will@...nel.org, anshuman.khandual@....com, ryan.roberts@....com,
 yang@...amperecomputing.com, joey.gouly@....com, stable@...r.kernel.org
Subject: Re: [PATCH v2] arm64: fix cleared E0POE bit after
 cpu_suspend()/resume()

On 07/01/2026 17:21, Yeoreum Yun wrote:
> TCR2_ELx.E0POE is set during smp_init().
> However, this bit is not reprogrammed when the CPU enters suspension and
> later resumes via cpu_resume(), as __cpu_setup() does not re-enable E0POE
> and there is no save/restore logic for the TCR2_ELx system register.
>
> As a result, the E0POE feature no longer works after cpu_resume().
>
> To address this, save and restore TCR2_EL1 in the cpu_suspend()/cpu_resume()
> path, rather than adding related logic to __cpu_setup(), taking into account
> possible future extensions of the TCR2_ELx feature.
>
> Cc: stable@...r.kernel.org
> Fixes: bf83dae90fbc ("arm64: enable the Permission Overlay Extension for EL0")
> Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> ---
>
> Patch History
> ==============
> from v1 to v2:
>   - following @Kevin Brodsky suggestion.
>   - https://lore.kernel.org/all/20260105200707.2071169-1-yeoreum.yun@arm.com/
>
> NOTE:
>   This patch based on v6.19-rc4
> ---
>  arch/arm64/include/asm/suspend.h | 2 +-
>  arch/arm64/mm/proc.S             | 8 ++++++++
>  2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/suspend.h b/arch/arm64/include/asm/suspend.h
> index e65f33edf9d6..e9ce68d50ba4 100644
> --- a/arch/arm64/include/asm/suspend.h
> +++ b/arch/arm64/include/asm/suspend.h
> @@ -2,7 +2,7 @@
>  #ifndef __ASM_SUSPEND_H
>  #define __ASM_SUSPEND_H
>
> -#define NR_CTX_REGS 13
> +#define NR_CTX_REGS 14
>  #define NR_CALLEE_SAVED_REGS 12
>
>  /*
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 01e868116448..5d907ce3b6d3 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -110,6 +110,10 @@ SYM_FUNC_START(cpu_do_suspend)
>  	 * call stack.
>  	 */
>  	str	x18, [x0, #96]
> +alternative_if ARM64_HAS_TCR2
> +	mrs	x2, REG_TCR2_EL1
> +	str	x2, [x0, #104]
> +alternative_else_nop_endif
>  	ret
>  SYM_FUNC_END(cpu_do_suspend)
>
> @@ -144,6 +148,10 @@ SYM_FUNC_START(cpu_do_resume)
>  	msr	tcr_el1, x8
>  	msr	vbar_el1, x9
>  	msr	mdscr_el1, x10
> +alternative_if ARM64_HAS_TCR2
> +	ldr	x2, [x0, #104]
> +	msr	REG_TCR2_EL1, x2
> +alternative_else_nop_endif

Maybe this could be pushed further down cpu_do_resume, next to DISR_EL1
maybe (since it's also conditional)? Otherwise the diff LGTM:

Reviewed-by: Kevin Brodsky <kevin.brodsky@....com>

- Kevin

>  	msr	sctlr_el1, x12
>  	set_this_cpu_offset x13
> --
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
>