linux-kernel - Re: [PATCH v4 11/21] KVM: arm64: Allow populating software bits

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Date:   Tue, 10 Aug 2021 06:56:51 +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 v4 11/21] KVM: arm64: Allow populating software bits

Hi Quentin,

On Mon, Aug 9, 2021 at 5:25 PM Quentin Perret <qperret@...gle.com> wrote:
>
> Introduce infrastructure allowing to manipulate software bits in stage-1
> and stage-2 page-tables using additional entries in the kvm_pgtable_prot
> enum.
>
> This is heavily inspired by Marc's implementation of a similar feature
> in the NV patch series, but adapted to allow stage-1 changes as well:
>
>   https://lore.kernel.org/kvmarm/20210510165920.1913477-56-maz@kernel.org/
>
> Suggested-by: Marc Zyngier <maz@...nel.org>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---

Reviewed-by: Fuad Tabba <tabba@...gle.com>

Thanks,
/fuad

>  arch/arm64/include/asm/kvm_pgtable.h | 12 +++++++++++-
>  arch/arm64/kvm/hyp/pgtable.c         |  5 +++++
>  2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 2c090b0eee77..ff9d52f8073a 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -121,6 +121,10 @@ enum kvm_pgtable_stage2_flags {
>   * @KVM_PGTABLE_PROT_W:                Write permission.
>   * @KVM_PGTABLE_PROT_R:                Read permission.
>   * @KVM_PGTABLE_PROT_DEVICE:   Device attributes.
> + * @KVM_PGTABLE_PROT_SW0:      Software bit 0.
> + * @KVM_PGTABLE_PROT_SW1:      Software bit 1.
> + * @KVM_PGTABLE_PROT_SW2:      Software bit 2.
> + * @KVM_PGTABLE_PROT_SW3:      Software bit 3.
>   */
>  enum kvm_pgtable_prot {
>         KVM_PGTABLE_PROT_X                      = BIT(0),
> @@ -128,6 +132,11 @@ enum kvm_pgtable_prot {
>         KVM_PGTABLE_PROT_R                      = BIT(2),
>
>         KVM_PGTABLE_PROT_DEVICE                 = BIT(3),
> +
> +       KVM_PGTABLE_PROT_SW0                    = BIT(55),
> +       KVM_PGTABLE_PROT_SW1                    = BIT(56),
> +       KVM_PGTABLE_PROT_SW2                    = BIT(57),
> +       KVM_PGTABLE_PROT_SW3                    = BIT(58),
>  };
>
>  #define KVM_PGTABLE_PROT_RW    (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
> @@ -420,7 +429,8 @@ kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr);
>   * If there is a valid, leaf page-table entry used to translate @addr, then
>   * relax the permissions in that entry according to the read, write and
>   * execute permissions specified by @prot. No permissions are removed, and
> - * TLB invalidation is performed after updating the entry.
> + * TLB invalidation is performed after updating the entry. Software bits cannot
> + * be set or cleared using kvm_pgtable_stage2_relax_perms().
>   *
>   * Return: 0 on success, negative error code on failure.
>   */
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index e25d829587b9..cff744136044 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -357,6 +357,7 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
>         attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S1_AP, ap);
>         attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S1_SH, sh);
>         attr |= KVM_PTE_LEAF_ATTR_LO_S1_AF;
> +       attr |= prot & KVM_PTE_LEAF_ATTR_HI_SW;
>         *ptep = attr;
>
>         return 0;
> @@ -558,6 +559,7 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
>
>         attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S2_SH, sh);
>         attr |= KVM_PTE_LEAF_ATTR_LO_S2_AF;
> +       attr |= prot & KVM_PTE_LEAF_ATTR_HI_SW;
>         *ptep = attr;
>
>         return 0;
> @@ -1025,6 +1027,9 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
>         u32 level;
>         kvm_pte_t set = 0, clr = 0;
>
> +       if (prot & KVM_PTE_LEAF_ATTR_HI_SW)
> +               return -EINVAL;
> +
>         if (prot & KVM_PGTABLE_PROT_R)
>                 set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
>
> --
> 2.32.0.605.g8dce9f2422-goog
>