linux-kernel - Re: [PATCH v3 16/21] KVM: arm64: Enable retrieving protections attributes of PTEs

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Message-ID: <CA+EHjTwL+grX__03SfeDdxeppjSovEZhKRvqjmA_4kSBwsjswg@mail.gmail.com>
Date:   Mon, 2 Aug 2021 16:52:49 +0200
From:   Fuad Tabba <tabba@...gle.com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, ardb@...nel.org, qwandor@...gle.com,
        dbrazdil@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH v3 16/21] KVM: arm64: Enable retrieving protections
 attributes of PTEs

Hi Quentin,

On Thu, Jul 29, 2021 at 3:29 PM Quentin Perret <qperret@...gle.com> wrote:
>
> Introduce helper functions in the KVM stage-2 and stage-1 page-table
> manipulation library allowing to retrieve the enum kvm_pgtable_prot of a
> PTE. This will be useful to implement custom walkers outside of
> pgtable.c.
>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 20 +++++++++++++++
>  arch/arm64/kvm/hyp/pgtable.c         | 37 ++++++++++++++++++++++++++++
>  2 files changed, 57 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index d5ca9b6ce241..7ff9f52239ba 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -505,4 +505,24 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
>   */
>  int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr,
>                          kvm_pte_t *ptep, u32 *level);
> +
> +/**
> + * kvm_pgtable_stage2_pte_prot() - Retrieve the protection attributes of a
> + *                                stage-2 Page-Table Entry.
> + * @pte:       Page-table entry
> + *
> + * Return: protection attributes of the page-table entry in the enum
> + *        kvm_pgtable_prot format.
> + */
> +enum kvm_pgtable_prot kvm_pgtable_stage2_pte_prot(kvm_pte_t pte);
> +
> +/**
> + * kvm_pgtable_hyp_pte_prot() - Retrieve the protection attributes of a stage-1
> + *                             Page-Table Entry.
> + * @pte:       Page-table entry
> + *
> + * Return: protection attributes of the page-table entry in the enum
> + *        kvm_pgtable_prot format.
> + */
> +enum kvm_pgtable_prot kvm_pgtable_hyp_pte_prot(kvm_pte_t pte);
>  #endif /* __ARM64_KVM_PGTABLE_H__ */
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 1915489bb127..a6eda8f23cb6 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -363,6 +363,26 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
>         return 0;
>  }
>
> +enum kvm_pgtable_prot kvm_pgtable_hyp_pte_prot(kvm_pte_t pte)
> +{
> +       enum kvm_pgtable_prot prot = pte & KVM_PTE_LEAF_ATTR_HI_SW;
> +       u32 ap;
> +
> +       if (!kvm_pte_valid(pte))
> +               return prot;
> +
> +       if (!(pte & KVM_PTE_LEAF_ATTR_HI_S1_XN))
> +               prot |= KVM_PGTABLE_PROT_X;
> +
> +       ap = FIELD_GET(KVM_PTE_LEAF_ATTR_LO_S1_AP, pte);
> +       if (ap == KVM_PTE_LEAF_ATTR_LO_S1_AP_RO)
> +               prot |= KVM_PGTABLE_PROT_R;
> +       else if (ap == KVM_PTE_LEAF_ATTR_LO_S1_AP_RW)
> +               prot |= KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W;

nit: why not use the freshly minted KVM_PGTABLE_PROT_RW?

Thanks,
/fuad


> +
> +       return prot;
> +}
> +
>  static bool hyp_pte_needs_update(kvm_pte_t old, kvm_pte_t new)
>  {
>         /*
> @@ -565,6 +585,23 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
>         return 0;
>  }
>
> +enum kvm_pgtable_prot kvm_pgtable_stage2_pte_prot(kvm_pte_t pte)
> +{
> +       enum kvm_pgtable_prot prot = pte & KVM_PTE_LEAF_ATTR_HI_SW;
> +
> +       if (!kvm_pte_valid(pte))
> +               return prot;
> +
> +       if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R)
> +               prot |= KVM_PGTABLE_PROT_R;
> +       if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W)
> +               prot |= KVM_PGTABLE_PROT_W;
> +       if (!(pte & KVM_PTE_LEAF_ATTR_HI_S2_XN))
> +               prot |= KVM_PGTABLE_PROT_X;
> +
> +       return prot;
> +}
> +
>  static bool stage2_pte_needs_update(kvm_pte_t old, kvm_pte_t new)
>  {
>         if (!kvm_pte_valid(old) || !kvm_pte_valid(new))
> --
> 2.32.0.432.gabb21c7263-goog
>