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

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Message-ID: <YQkZTnVLwVYDFvoA@google.com>
Date:   Tue, 3 Aug 2021 11:24:14 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Fuad Tabba <tabba@...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

On Monday 02 Aug 2021 at 16:52:49 (+0200), Fuad Tabba wrote:
> 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?

No good reason, I'll fix that up, thanks!