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

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Message-ID: <CAKHBV26sRpFJv8-_f4n2jsTKiOgnHF0_FZ07KBbVaueX+T2kWA@mail.gmail.com>
Date:   Thu, 27 Jul 2023 19:22:05 +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

Sorry for the delay; I'm trying to refactor these patches now.

> I think the master should have a pointer to the iommu_domain that owns
> the STE or if NULL the master should assign its internal CD table to
> the STE.
Just to clarify, does the nested domain patch series require writing
CDs into the user-space's CD table using arm_smmu_write_ctx_desc()? Or
is there any other requirement for writing a CD into a domain-owned CD
table from arm_smmu_write_ctx_desc?

Writing a CD entry to the CD table involves some dependencies on the
master(s) that the table is attached to:

1. The CD entries STALL bit value in arm_smmu_write_ctx_desc depends
on the master (e.g. if STALL_FORCE is set on the smmu device). This
could potentially be encoded in arm_smmu_ctx_desc_cfg, at which point
that CD table is only attachable to masters with the same
stall_enabled value.
2. arm_smmu_write_ctx_desc must sync the CD for the attached master(s)
in the middle of writing CD entry.

This is all easier to handle in arm_smmu_write_ctx_desc if the table
is always owned by the master.