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Now that the XArray makes SID lookup O(1), detect aliasing at group-assignment time and place the new device into the same IOMMU group as the master that already owns the SID. This is a prerequisite for shared-SID support: devices sharing a SID must share a single IOMMU domain and therefore a single cd_table, because the STE can only point to one cd_table at a time. arm_smmu_device_group() is called before arm_smmu_insert_master() adds the current master's streams to the xarray, so any xarray hit here belongs to a different, already-probed master. streams_mutex is held to ensure the xarray is stable and the returned stream object is not freed concurrently. If a device has multiple SIDs that land in different existing groups, a warning is emitted. The IOMMU core has no group-merge API, so this cannot be fixed up and DMA isolation may be compromised. Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Peng Fan --- drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 61 +++++++++++++++++++++++++---- 1 file changed, 53 insertions(+), 8 deletions(-) diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c index f53e1871426a5..bb3ee25d10d6e 100644 --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c @@ -4365,19 +4365,64 @@ static int arm_smmu_set_dirty_tracking(struct iommu_domain *domain, static struct iommu_group *arm_smmu_device_group(struct device *dev) { - struct iommu_group *group; + struct arm_smmu_master *master = dev_iommu_priv_get(dev); + struct arm_smmu_device *smmu = master->smmu; + struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev); + struct iommu_group *group = NULL; + int i; /* - * We don't support devices sharing stream IDs other than PCI RID - * aliases, since the necessary ID-to-device lookup becomes rather - * impractical given a potential sparse 32-bit stream ID space. + * If any of this device's SIDs are already owned by another master, + * place this device in the same IOMMU group as that master. This + * ensures that aliasing devices share a single domain and therefore + * a single cd_table, which is required because the STE can only + * point to one cd_table at a time. + * + * arm_smmu_device_group() is called before arm_smmu_insert_master() + * adds the current master's streams to the xarray, so any hit here + * belongs to a different, already-probed master. + * + * streams_mutex is held to ensure the xarray is stable and the + * returned stream object is not freed concurrently. */ + mutex_lock(&smmu->streams_mutex); + for (i = 0; i < fwspec->num_ids; i++) { + struct arm_smmu_stream *stream = + xa_load(&smmu->streams, fwspec->ids[i]); + struct iommu_group *existing; + + if (!stream) + continue; + + existing = iommu_group_get(stream->master->dev); + if (!group) { + group = existing; + } else if (group != existing) { + /* + * This device has SIDs in two different groups. + * The IOMMU core has no group-merge API, so we + * cannot fix this up. Warn and keep the first + * group — the mismatched SID will still be + * inserted into the XArray and shared, but DMA + * isolation is compromised. + */ + dev_warn(dev, + "SID 0x%x already in a different IOMMU group than SID 0x%x, expect broken isolation\n", + fwspec->ids[i], fwspec->ids[0]); + iommu_group_put(existing); + } else { + iommu_group_put(existing); + } + } + mutex_unlock(&smmu->streams_mutex); + + if (group) + return group; + if (dev_is_pci(dev)) - group = pci_device_group(dev); - else - group = generic_device_group(dev); + return pci_device_group(dev); - return group; + return generic_device_group(dev); } static int arm_smmu_of_xlate(struct device *dev, -- 2.34.1