[PATCH v5 10/14] KVM: arm64: Split init and set for table PTE

[Ben Gardon]

On Mon, Nov 7, 2022 at 1:58 PM Oliver Upton <oliver.upton at linux.dev> wrote:
>
> Create a helper to initialize a table and directly call
> smp_store_release() to install it (for now). Prepare for a subsequent
> change that generalizes PTE writes with a helper.
>
> Signed-off-by: Oliver Upton <oliver.upton at linux.dev>
> ---
>  arch/arm64/kvm/hyp/pgtable.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index a34e2050f931..f4dd77c6c97d 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -136,16 +136,13 @@ static void kvm_clear_pte(kvm_pte_t *ptep)
>         WRITE_ONCE(*ptep, 0);
>  }
>
> -static void kvm_set_table_pte(kvm_pte_t *ptep, kvm_pte_t *childp,
> -                             struct kvm_pgtable_mm_ops *mm_ops)
> +static kvm_pte_t kvm_init_table_pte(kvm_pte_t *childp, struct kvm_pgtable_mm_ops *mm_ops)
>  {
> -       kvm_pte_t old = *ptep, pte = kvm_phys_to_pte(mm_ops->virt_to_phys(childp));
> +       kvm_pte_t pte = kvm_phys_to_pte(mm_ops->virt_to_phys(childp));
>
>         pte |= FIELD_PREP(KVM_PTE_TYPE, KVM_PTE_TYPE_TABLE);
>         pte |= KVM_PTE_VALID;
> -
> -       WARN_ON(kvm_pte_valid(old));

Is there any reason to drop this warning?


> -       smp_store_release(ptep, pte);
> +       return pte;
>  }
>
>  static kvm_pte_t kvm_init_valid_leaf_pte(u64 pa, kvm_pte_t attr, u32 level)
> @@ -413,7 +410,7 @@ static bool hyp_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
>  static int hyp_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
>                           enum kvm_pgtable_walk_flags visit)
>  {
> -       kvm_pte_t *childp;
> +       kvm_pte_t *childp, new;
>         struct hyp_map_data *data = ctx->arg;
>         struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
>
> @@ -427,8 +424,10 @@ static int hyp_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
>         if (!childp)
>                 return -ENOMEM;
>
> -       kvm_set_table_pte(ctx->ptep, childp, mm_ops);
> +       new = kvm_init_table_pte(childp, mm_ops);
>         mm_ops->get_page(ctx->ptep);
> +       smp_store_release(ctx->ptep, new);
> +
>         return 0;
>  }
>
> @@ -796,7 +795,7 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
>                                 struct stage2_map_data *data)
>  {
>         struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> -       kvm_pte_t *childp;
> +       kvm_pte_t *childp, new;
>         int ret;
>
>         ret = stage2_map_walker_try_leaf(ctx, data);
> @@ -821,8 +820,9 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
>         if (stage2_pte_is_counted(ctx->old))
>                 stage2_put_pte(ctx, data->mmu, mm_ops);
>
> -       kvm_set_table_pte(ctx->ptep, childp, mm_ops);
> +       new = kvm_init_table_pte(childp, mm_ops);
>         mm_ops->get_page(ctx->ptep);
> +       smp_store_release(ctx->ptep, new);
>
>         return 0;
>  }
> --
> 2.38.1.431.g37b22c650d-goog
>