linux-kernel - Re: [PATCH v6 07/24] arm64: Make PMR part of task context

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Message-ID: <20181204170908.GB19210@arrakis.emea.arm.com>
Date:   Tue, 4 Dec 2018 17:09:08 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Julien Thierry <julien.thierry@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, daniel.thompson@...aro.org,
        marc.zyngier@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, christoffer.dall@....com,
        james.morse@....com, joel@...lfernandes.org,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v6 07/24] arm64: Make PMR part of task context

On Mon, Nov 12, 2018 at 11:56:58AM +0000, Julien Thierry wrote:
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 039144e..eb8120e 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -249,6 +249,12 @@ alternative_else_nop_endif
>  	msr	sp_el0, tsk
>  	.endif
>  
> +	/* Save pmr */
> +alternative_if ARM64_HAS_IRQ_PRIO_MASKING
> +	mrs_s	x20, SYS_ICC_PMR_EL1
> +	str	x20, [sp, #S_PMR_SAVE]
> +alternative_else_nop_endif
> +
>  	/*
>  	 * Registers that may be useful after this macro is invoked:
>  	 *
> @@ -269,6 +275,13 @@ alternative_else_nop_endif
>  	/* No need to restore UAO, it will be restored from SPSR_EL1 */
>  	.endif
>  
> +	/* Restore pmr */
> +alternative_if ARM64_HAS_IRQ_PRIO_MASKING
> +	ldr	x20, [sp, #S_PMR_SAVE]
> +	msr_s	SYS_ICC_PMR_EL1, x20
> +	dsb	sy
> +alternative_else_nop_endif

What's this DSB for? If it's needed, please add a comment.

I would have expected an ISB (or none at all as we are going to return
from an exception).

-- 
Catalin