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 01:56:12 +0800
From:   Michael Shavit <mshavit@...gle.com>
To:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     will@...nel.org, robin.murphy@....com, nicolinc@...dia.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

This patch introduces a subtle bug.

Previously, the arm-smmu-v3 driver could get away with skipping the
clearing of the CD entry on detach, since the table belonged to the
domain and wouldn't be re-written on re-attach. When we switch to the
master-owned table model, that CDTE in the master's table can get
written to with different CD domains. When the CD domain get's
switched to a new one without first being cleared, arm_smmu_write_ctx
will mis-interpret its call as an ASID update instead of an entirely
new Cd.

This bug was handled by clearing the CD entry on detach in the
"iommu/arm-smmu-v3: Refactor write_ctx_desc" commit before it was
split from the set_dev_pasid
series(https://lore.kernel.org/all/20230621063825.268890-5-mshavit@google.com/).
The change was lost when the commit moved to this series however. It's
splitting hairs a little, but that fix probably belongs in this patch
instead.