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Date:   Tue, 23 Mar 2021 09:47:08 +0000
From:   Quentin Perret <qperret@google.com>
To:     Marc Zyngier <maz@kernel.org>
Cc:     catalin.marinas@arm.com, james.morse@arm.com,
        julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com,
        android-kvm@google.com, seanjc@google.com, mate.toth-pal@arm.com,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kernel-team@android.com, kvmarm@lists.cs.columbia.edu,
        tabba@google.com, ardb@kernel.org, mark.rutland@arm.com,
        dbrazdil@google.com
Subject: Re: [PATCH 2/3] KVM: arm64: Generate final CTR_EL0 value when
 running in Protected mode
Message-ID: <YFm5HIC/2Toowhnx@google.com>
References: <20210322164828.800662-1-maz@kernel.org>
 <20210322164828.800662-3-maz@kernel.org>
 <YFjWmHerKk7+9d7N@google.com>
 <87k0pzghlx.wl-maz@kernel.org>
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Hi Marc,

On Monday 22 Mar 2021 at 18:37:14 (+0000), Marc Zyngier wrote:
> Can't say I'm keen on the yucky bit, but here's an alternative (ha!)
> for you:
> 
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index 1a4cee7eb3c9..7582c3bd2f05 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -278,6 +278,9 @@ alternative_else
>  	ldr_l	\reg, arm64_ftr_reg_ctrel0 + ARM64_FTR_SYSVAL
>  alternative_endif
>  #else
> +alternative_if_not ARM64_KVM_PROTECTED_MODE
> +	ASM_BUG()
> +alternative_else_nop_endif
>  alternative_cb kvm_compute_final_ctr_el0
>  	movz	\reg, #0
>  	movk	\reg, #0, lsl #16
> 
> Yes, it is one more instruction, but it is cleaner and allows us to
> from the first patch of the series.
> 
> What do you think?

Yes, I think having the ASM_BUG() in this macro is bit nicer and I doubt
the additional nop will make any difference, so this is looking good to
me!

Thanks,
Quentin