RE: [PATCH v7 03/10] iommu/sva: Add iommu_sva_domain support

Tian, Kevin
2022-05-24T09:40:10Z

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Thursday, May 19, 2022 3:21 PM
>
> The iommu_sva_domain represents a hardware pagetable that the IOMMU
> hardware could use for SVA translation. This adds some infrastructure
> to support SVA domain in the iommu common layer. It includes:
>
> - Add a new struct iommu_sva_domain and new IOMMU_DOMAIN_SVA
> domain
> type.
> - Add a new domain ops pointer in iommu_ops. The IOMMU drivers that
> support SVA should provide the callbacks.
> - Add helpers to allocate and free an SVA domain.
> - Add helpers to set an SVA domain to a device and the reverse
> operation.
>
> Some buses, like PCI, route packets without considering the PASID value.
> Thus a DMA target address with PASID might be treated as P2P if the
> address falls into the MMIO BAR of other devices in the group. To make
> things simple, the attach/detach interfaces only apply to devices
> belonging to the singleton groups, and the singleton is immutable in
> fabric i.e. not affected by hotplug.
>
> The iommu_set/block_device_pasid() can be used for other purposes,
> such as kernel DMA with pasid, mediation device, etc. Hence, it is put
> in the iommu.c.

usually we have 'set/clear' pair or 'allow/block'. Having 'set' paired
with 'block' doesn't read very clearly.

> +static bool device_group_immutable_singleton(struct device *dev)
> +{
> + struct iommu_group *group = iommu_group_get(dev);

what about passing group as the parameter since the caller will
get the group again right after calling this function? In that case
the function could be renamed as:

iommu_group_immutable_singleton()

or be shorter:

iommu_group_fixed_singleton()

> + int count;
> +
> + if (!group)
> + return false;
> +
> + mutex_lock(&group->mutex);
> + count = iommu_group_device_count(group);
> + mutex_unlock(&group->mutex);
> + iommu_group_put(group);
> +
> + if (count != 1)
> + return false;

For non-pci devices above doesn't check anything against immutable.
Please add some comment to explain why doing so is correct.

> +
> + /*
> + * The PCI device could be considered to be fully isolated if all
> + * devices on the path from the device to the host-PCI bridge are
> + * protected from peer-to-peer DMA by ACS.
> + */
> + if (dev_is_pci(dev))
> + return pci_acs_path_enabled(to_pci_dev(dev), NULL,
> + REQ_ACS_FLAGS);
> +
> + return true;
> +}
> +