Re: [PATCH v4 6/8] iommu/arm-smmu-v3: Move CD table to arm_smmu_master

[Michael Shavit]

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@xxxxxxxxxx/).
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.