linux-kernel - Re: [PATCH v5 1/6] KVM: arm64: Introduce KVM_PGTABLE_S2

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Date:   Wed, 2 Jun 2021 10:43:40 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Yanan Wang <wangyanan55@...wei.com>
Cc:     Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Alexandru Elisei <alexandru.elisei@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Gavin Shan <gshan@...hat.com>, wanghaibin.wang@...wei.com,
        zhukeqian1@...wei.com, yuzenghui@...wei.com
Subject: Re: [PATCH v5 1/6] KVM: arm64: Introduce KVM_PGTABLE_S2_GUEST
 stage-2 flag

Hi Yanan,

On Thursday 15 Apr 2021 at 19:50:27 (+0800), Yanan Wang wrote:
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index c3674c47d48c..a43cbe697b37 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -61,10 +61,12 @@ struct kvm_pgtable_mm_ops {
>   * @KVM_PGTABLE_S2_NOFWB:	Don't enforce Normal-WB even if the CPUs have
>   *				ARM64_HAS_STAGE2_FWB.
>   * @KVM_PGTABLE_S2_IDMAP:	Only use identity mappings.
> + * @KVM_PGTABLE_S2_GUEST:	Whether the page-tables are guest stage-2.
>   */
>  enum kvm_pgtable_stage2_flags {
>  	KVM_PGTABLE_S2_NOFWB			= BIT(0),
>  	KVM_PGTABLE_S2_IDMAP			= BIT(1),
> +	KVM_PGTABLE_S2_GUEST			= BIT(2),

Assuming that we need this flag (maybe not given Marc's suggestion on
another patch), I'd recommend re-naming it to explain _what_ it does,
rather than _who_ is using it.

That's the principle we followed for e.g. KVM_PGTABLE_S2_IDMAP, so we
should be consistent here as well.

Thanks,
Quentin