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Date:   Sat, 23 Jan 2021 14:07:53 +0000
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Marc Zyngier <maz@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        David Brazdil <dbrazdil@google.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Jing Zhang <jingzhangos@google.com>,
        Ajay Patil <pajay@qti.qualcomm.com>,
        Prasad Sodagudi <psodagud@codeaurora.org>,
        Srinivas Ramana <sramana@codeaurora.org>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        kernel-team@android.com
Subject: Re: [PATCH v4 14/21] arm64: Honor VHE being disabled from the
 command-line
Message-ID: <YAwtuZZpTwwoMqrk@Catalins-MacBook-Air.local>
References: <20210118094533.2874082-1-maz@kernel.org>
 <20210118094533.2874082-15-maz@kernel.org>
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On Mon, Jan 18, 2021 at 09:45:26AM +0000, Marc Zyngier wrote:
> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> index 59820f9b8522..bbab2148a2a2 100644
> --- a/arch/arm64/kernel/hyp-stub.S
> +++ b/arch/arm64/kernel/hyp-stub.S
> @@ -77,13 +77,24 @@ SYM_CODE_END(el1_sync)
>  SYM_CODE_START_LOCAL(mutate_to_vhe)
>  	// Sanity check: MMU *must* be off
>  	mrs	x0, sctlr_el2
> -	tbnz	x0, #0, 1f
> +	tbnz	x0, #0, 2f
>  
>  	// Needs to be VHE capable, obviously
>  	mrs	x0, id_aa64mmfr1_el1
>  	ubfx	x0, x0, #ID_AA64MMFR1_VHE_SHIFT, #4
> -	cbz	x0, 1f
> +	cbz	x0, 2f
>  
> +	// Check whether VHE is disabled from the command line
> +	adr_l	x1, id_aa64mmfr1_val
> +	ldr	x0, [x1]
> +	adr_l	x1, id_aa64mmfr1_mask
> +	ldr	x1, [x1]
> +	ubfx	x0, x0, #ID_AA64MMFR1_VHE_SHIFT, #4
> +	ubfx	x1, x1, #ID_AA64MMFR1_VHE_SHIFT, #4
> +	cbz	x1, 1f
> +	and	x0, x0, x1
> +	cbz	x0, 2f
> +1:

I can see the advantage here in separate id_aa64mmfr1_val/mask but we
could use some asm offsets here and keep the pointer indirection simpler
in C code. You'd just need something like 'adr_l mmfr1_ovrd + VAL_OFFSET'.

Anyway, if you have a strong preference for the current approach, leave
it as is.

-- 
Catalin