linux-kernel - Re: [PATCH v5 14/36] KVM: arm64: Provide __flush_dcache

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Date:   Mon, 15 Mar 2021 16:33:23 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     catalin.marinas@....com, maz@...nel.org, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        android-kvm@...gle.com, seanjc@...gle.com, mate.toth-pal@....com,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kernel-team@...roid.com,
        kvmarm@...ts.cs.columbia.edu, tabba@...gle.com, ardb@...nel.org,
        mark.rutland@....com, dbrazdil@...gle.com
Subject: Re: [PATCH v5 14/36] KVM: arm64: Provide __flush_dcache_area at EL2

On Mon, Mar 15, 2021 at 02:35:14PM +0000, Quentin Perret wrote:
> We will need to do cache maintenance at EL2 soon, so compile a copy of
> __flush_dcache_area at EL2, and provide a copy of arm64_ftr_reg_ctrel0
> as it is needed by the read_ctr macro.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_cpufeature.h |  2 ++
>  arch/arm64/kvm/hyp/nvhe/Makefile        |  3 ++-
>  arch/arm64/kvm/hyp/nvhe/cache.S         | 13 +++++++++++++
>  arch/arm64/kvm/sys_regs.c               |  1 +
>  4 files changed, 18 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/cache.S
> 
> diff --git a/arch/arm64/include/asm/kvm_cpufeature.h b/arch/arm64/include/asm/kvm_cpufeature.h
> index 3fd9f60d2180..efba1b89b8a4 100644
> --- a/arch/arm64/include/asm/kvm_cpufeature.h
> +++ b/arch/arm64/include/asm/kvm_cpufeature.h
> @@ -13,3 +13,5 @@
>  #define KVM_HYP_CPU_FTR_REG(name) extern struct arm64_ftr_reg kvm_nvhe_sym(name)
>  #endif
>  #endif
> +
> +KVM_HYP_CPU_FTR_REG(arm64_ftr_reg_ctrel0);

I still think this is a bit weird. If you really want to macro-ise stuff,
then why not follow the sort of thing we do for e.g. per-cpu variables and
have separate DECLARE_HYP_CPU_FTR_REG and DEFINE_HYP_CPU_FTR_REG macros.

That way kvm_cpufeature.h can have header guards like a normal header and
we can drop the '#ifndef KVM_HYP_CPU_FTR_REG' altogether. I don't think
the duplication of the symbol name really matters -- it should fail at
build time if something is missing.

Will