linux-kernel - Re: [PATCH v4 6/8] iommu/arm-smmu-v3: Move CD table to arm_smmu

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Date:   Fri, 4 Aug 2023 15:25:43 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Michael Shavit <mshavit@...gle.com>
CC:     <iommu@...ts.linux.dev>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <will@...nel.org>,
        <robin.murphy@....com>, <jgg@...dia.com>,
        <jean-philippe@...aro.org>
Subject: Re: [PATCH v4 6/8] iommu/arm-smmu-v3: Move CD table to
 arm_smmu_master

On Thu, Aug 03, 2023 at 12:32:34AM +0800, Michael Shavit wrote:
> +static int arm_smmu_alloc_cd_tables(struct arm_smmu_master *master)
>  {
>         int ret;
>         size_t l1size;
>         size_t max_contexts;
>         struct arm_smmu_device *smmu = master->smmu;
> -       struct arm_smmu_ctx_desc_cfg *cdcfg = &smmu_domain->cd_table;
> +       struct arm_smmu_ctx_desc_cfg *cdcfg = &master->cd_table;
> 
>         cdcfg->stall_enabled = master->stall_enabled;

We have stall_enabled at both master->cd_table->stall_enabled
and master->stall_enabled, and we removed stall_enabled from
the CD structure...

> @@ -2436,22 +2419,14 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>         if (!smmu_domain->smmu) {
>                 smmu_domain->smmu = smmu;
>                 ret = arm_smmu_domain_finalise(domain, master);
> -               if (ret) {
> +               if (ret)
>                         smmu_domain->smmu = NULL;
> -                       goto out_unlock;
> -               }
> -       } else if (smmu_domain->smmu != smmu) {
> +       } else if (smmu_domain->smmu != smmu)
>                 ret = -EINVAL;
> -               goto out_unlock;
> -       } else if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1 &&
> -                  master->ssid_bits != smmu_domain->cd_table.max_cds_bits) {
> -               ret = -EINVAL;
> -               goto out_unlock;
> -       } else if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1 &&
> -                  smmu_domain->cd_table.stall_enabled != master->stall_enabled) {
> -               ret = -EINVAL;
> -               goto out_unlock;
> -       }

... then we remove this stall_enabled sanity also.

This means a shared domain (holding a shared CD) being inserted
to two CD tables from two masters would have two different CDTE
configurations at the stall bit.

If this is fine (I can't think of something wrong but not sure),
it would be okay here, though I feel we could mention this some-
where (maybe commit logs) since it changes the attach behavior?

Thanks
Nicolin