Re: [PATCH 2/5] iommu: Allocate a default domain for iommu groups

Will Deacon
2015-01-28T20:28:10Z

On Tue, Jan 27, 2015 at 12:08:56AM +0000, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> The default domain will be used (if supported by the iommu
> driver) when the devices in the iommu group are not attached
> to any other domain.
>
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> drivers/iommu/iommu.c | 26 +++++++++++++++++++++++---
> 1 file changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 34636eb..8f33ddd3 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -76,6 +76,9 @@ struct iommu_group_attribute iommu_group_attr_##_name = \
> #define to_iommu_group(_kobj) \
> container_of(_kobj, struct iommu_group, kobj)
>
> +static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
> + enum iommu_domain_type type);
> +
> static ssize_t iommu_group_attr_show(struct kobject *kobj,
> struct attribute *__attr, char *buf)
> {
> @@ -362,6 +365,17 @@ rename:
>
> kobject_get(group->devices_kobj);
>
> + /*
> + * Try to allocate a default domain for the group, if this
> + * hasn't happened yet. This is not the best place to do that,
> + * it should happen in iommu_group_alloc(). But we have no
> + * iommu_ops there yet, so the allocation has to happen here for
> + * now.
> + */
> + if (group->default_domain == NULL)
> + group->default_domain = __iommu_domain_alloc(dev->bus,
> + IOMMU_DOMAIN_DMA);

Having a per-group domain is wasteful for IOMMUs that only support a modest
number of concurrent domains, so in reality I think we need to have one
domain per IOMMU instance. Is that possible?

One problem with the current per-bus approach is that __iommu_domain_alloc
can't figure out which IOMMU instance corresponds to the group.

Will