[PATCH 12/19] iommu/arm-smmu-v3: Put writing the context descriptor in the right order

[Michael Shavit]

On Wed, Oct 11, 2023 at 8:33 AM Jason Gunthorpe <jgg at nvidia.com> wrote:
> If we are replacing a CD table entry when the STE already points at the CD
> entry then we just need to do the make/break sequence.

Do you mean when the STE already points at the CD table? What's the
make/break sequence?


>  static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> @@ -2554,6 +2546,17 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>                                 master->domain = NULL;
>                                 goto out_list_del;
>                         }
> +               } else {
> +                       /*
> +                        * arm_smmu_write_ctx_desc() relies on the entry being
> +                        * invalid to work, clear any existing entry.
> +                        */
> +                       ret = arm_smmu_write_ctx_desc(master, IOMMU_NO_PASID,
> +                                                     NULL);
> +                       if (ret) {
> +                               master->domain = NULL;
> +                               goto out_list_del;
> +                       }
>                 }
>
>                 ret = arm_smmu_write_ctx_desc(master, IOMMU_NO_PASID, &smmu_domain->cd);
> @@ -2563,15 +2566,23 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>                 }
>
>                 arm_smmu_make_cdtable_ste(&target, master, &master->cd_table);
> +               arm_smmu_install_ste_for_dev(master, &target);

Even if it's handled correctly under the hood by clever ste writing
logic, isn't it weird that we don't explicitly check whether the CD
table is already installed and skip arm_smmu_install_ste_for_dev in
that case?