linux-kernel - Re: [PATCH 06/15] arm64: kvm: Move __smccc_workaround_1

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Date:   Mon, 11 May 2020 11:04:59 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     David Brazdil <dbrazdil@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/15] arm64: kvm: Move __smccc_workaround_1_smc to
 .rodata

On Thu, 30 Apr 2020 15:48:22 +0100
David Brazdil <dbrazdil@...gle.com> wrote:

> This snippet of assembly is used by cpu_errata.c to overwrite parts of KVM hyp
> vector. It is never directly executed, so move it from .text to .rodata.
> 
> Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> ---
>  arch/arm64/kvm/hyp/hyp-entry.S | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index 5986e1d78d3f..7e5f386c5c2d 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -364,6 +364,11 @@ SYM_CODE_END(__bp_harden_hyp_vecs)
>  	.popsection
>  
>  #ifndef __HYPERVISOR__
> +	/*
> +	 * This is not executed directly and is instead copied into the vectors
> +	 * by install_bp_hardening_cb().
> +	 */
> +	.pushsection	.rodata
>  SYM_CODE_START(__smccc_workaround_1_smc)

I wonder whether we should keep the SYM_CODE_START() annotation or not.
It feels weird to say "code" in a rodata section, and the alignment
doesn't matter as we copy it in place, as you noticed.

>  	esb
>  	sub	sp, sp, #(8 * 4)
> @@ -377,5 +382,6 @@ SYM_CODE_START(__smccc_workaround_1_smc)
>  1:	.org __smccc_workaround_1_smc + __SMCCC_WORKAROUND_1_SMC_SZ
>  	.org 1b
>  SYM_CODE_END(__smccc_workaround_1_smc)
> +	.popsection
>  #endif /* __HYPERVISOR__ */
>  #endif /* CONFIG_KVM_INDIRECT_VECTORS */

Otherwise, looks good.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...