linux-kernel - Re: [PATCH v6 33/38] KVM: arm64: Introduce KVM_PGTABLE_S2

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Date:   Mon, 22 Mar 2021 11:33:20 +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 v6 33/38] KVM: arm64: Introduce KVM_PGTABLE_S2_IDMAP
 stage 2 flag

On Fri, Mar 19, 2021 at 10:01:41AM +0000, Quentin Perret wrote:
> Introduce a new stage 2 configuration flag to specify that all mappings
> in a given page-table will be identity-mapped, as will be the case for
> the host. This allows to introduce sanity checks in the map path and to
> avoid programming errors.
> 
> Suggested-by: Will Deacon <will@...nel.org>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 2 ++
>  arch/arm64/kvm/hyp/pgtable.c         | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 55452f4831d2..c3674c47d48c 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -60,9 +60,11 @@ struct kvm_pgtable_mm_ops {
>   * enum kvm_pgtable_stage2_flags - Stage-2 page-table flags.
>   * @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.
>   */
>  enum kvm_pgtable_stage2_flags {
>  	KVM_PGTABLE_S2_NOFWB			= BIT(0),
> +	KVM_PGTABLE_S2_IDMAP			= BIT(1),
>  };
>  
>  /**
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index b22b4860630c..c37c1dc4feaf 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -760,6 +760,9 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
>  		.arg		= &map_data,
>  	};
>  
> +	if (WARN_ON((pgt->flags & KVM_PGTABLE_S2_IDMAP) && (addr != phys)))
> +		return -EINVAL;

Acked-by: Will Deacon <will@...nel.org>

Will