linux-kernel - Re: [PATCH v4 02/13] iommu/arm-smmu-v3: Add smmu_s1_cfg to smmu

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Date:   Wed, 12 Jul 2023 18:22:17 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Michael Shavit <mshavit@...gle.com>
CC:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        "Joerg Roedel" <joro@...tes.org>, <jean-philippe@...aro.org>,
        <jgg@...dia.com>, <baolu.lu@...ux.intel.com>,
        <linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 02/13] iommu/arm-smmu-v3: Add smmu_s1_cfg to
 smmu_master

Hi Michael,

On Wed, Jun 21, 2023 at 02:37:14PM +0800, Michael Shavit wrote:

> Except for Nested domains, arm_smmu_master will own the STEs that are
> inserted into the arm_smmu_device's STE table.

I think that the master still owns an STE when attached to a
nested domain. Though an IOMMU_DOMAIN_NESTED iommu_domain is
an opaque object to the STE in the guest, the host still has
a real STE for the nested configuration somewhere -- and it's
likely still to be owned by the master that's attached to the
opaque NESTED iommu_domain in the host kernel.

> -static int arm_smmu_alloc_cd_tables(struct arm_smmu_domain *smmu_domain)
> +static int arm_smmu_init_s1_cfg(struct arm_smmu_master *master,
> +                               struct arm_smmu_s1_cfg *cfg)

We here pass in an s1_cfg ptr because we expect someone else
rather than the master could own the s1_cfg?

But the final codeline by the end of this series seems that
only master owns an s1_cfg. So perhaps we could re-organize
the patches to clean this away, as the cfg always comes from
a master?

> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> index 68d519f21dbd8..053cc14c23969 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -688,6 +688,7 @@ struct arm_smmu_master {
>         struct arm_smmu_domain          *domain;
>         struct list_head                domain_head;
>         struct arm_smmu_stream          *streams;
> +       struct arm_smmu_s1_cfg          owned_s1_cfg;

I am a bit confused by this naming. If only master would own
an s1_cfg, perhaps we can just make it "s1_cfg" and drop the
s1_cfg pointer in the next patch.

Thanks
Nicolin