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

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Date:   Fri, 14 Jul 2023 00:16:16 +0800
From:   Michael Shavit <mshavit@...gle.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Nicolin Chen <nicolinc@...dia.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, jean-philippe@...aro.org,
        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

On Thu, Jul 13, 2023 at 10:29 PM Jason Gunthorpe <jgg@...dia.com> wrote:
> It would make alot more sense if the STE value used by an unmanaged S1
> domain was located in/near the unmanaged domain or called 'unmanaged
> S1 STE' or something if it really has to be in the master. Why does
> this even need to be stored, can't we compute it?

struct s1_cfg* and struct s2_cfg* are precisely what is used to
compute an STE. For example, when s1_cfg is set, arm_smmu_write_strtab
will write the s1_cfg's CD table dma_pointer into the STE's
STRTAB_STE_0_CFG field. When neither are set, the STE fields are
written to enable bypass (or abort depending on the config).

> I'd think the basic mental model should be to extract the STE from the
> thing you intend to install. Either the default CD table, or from the
> iommu_domain. ie some 'get STE from iommu_domain' function?

I don't follow this. When we attach a domain with pasid (whether
through SVA or the set_dev_pasid API) , we don't want to install an
entirely new CD table. We want to write something (page-table pointer)
to a common CD table. Where should the s1_cfg which owns that common
table live? I thought we concluded that it should be owned by the
arm_smmu_master rather than any domain (to avoid dependencies between
domains a-la aux-domain). With this change, even attach_dev with a DMA
or UNMANAGED domain is now just preparing a single entry into this
common CD table.