linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: Simplify stage selection logic

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Date:   Fri, 18 Aug 2023 01:06:48 +0800
From:   Michael Shavit <mshavit@...gle.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     iommu@...ts.linux.dev, Jason Gunthorpe <jgg@...pe.ca>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Nicolin Chen <nicolinc@...dia.com>,
        Tomas Krcka <krckatom@...zon.de>,
        Will Deacon <will@...nel.org>,
        Yicong Yang <yangyicong@...ilicon.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu-v3: Simplify stage selection logic

On Fri, Aug 18, 2023 at 12:35 AM Robin Murphy <robin.murphy@....com> wrote:
>
> The reason it's like this is because of arm_smmu_enable_nesting(), which
> *is* the additional thing that's going on with the stage selection logic.
>
> Thanks,
> Robin.

Right, but arm_smmu_enable_nesting isn't involved in this computation
at this point in the flow.

arm_smmu_enable_nesting returns early if smmu_domain->smmu isn't set,
and smmu_domain->smmu is only set after arm_smmu_domain_finalise.
So at this point, smmu_domain->stage is being initialized for the
first time. If this code is responsible for handling some special
nesting case, then it's probably not working as intended.