[RFC PATCH 01/30] iommu/arm-smmu-v3: Link groups and devices

Robin Murphy
2017-03-27T12:18:39Z

Hi Jean-Philippe,

On 27/02/17 19:54, Jean-Philippe Brucker wrote:
> Reintroduce smmu_group. This structure was removed during the generic DT
> bindings rework, but will be needed when implementing PCIe ATS, to lookup
> devices attached to a given domain.
>
> When unmapping from a domain, we need to send an invalidation to all
> devices that could have stored the mapping in their ATC. It would be nice
> to use IOMMU API's iommu_group_for_each_dev, but that list is protected by
> group->mutex, which we can't use because atc_invalidate won't be allowed
> to sleep. So add a list of devices, protected by a spinlock.

Much as I dislike that particular duplication, with patch #4 in mind I
think there's a more fundamental problem - since the primary reason for
multi-device groups is lack of ACS, is there any guarantee that ATS
support/enablement will be actually be homogeneous across any old set of
devices in that situation, and thus valid to evaluate at the iommu_group
level?

That said, looking at how things end up at the top commit, I think this
is fairly easily sidestepped. We have this pattern a few times:

spin_lock_irqsave(&smmu_domain->groups_lock)
list_for_each_entry(&smmu_domain->groups)
spin_lock(&smmu_group->devices_lock)
list_for_each_entry(&smmu_group->devices)
do a thing for each device in the domain...

which strongly suggests that we'd be better off just linking the devices
to the domain directly - which would also let us scope ats_enabled to
the per-device level which seems safer than per-group as above. And if
only devices with ATS enabled are added to a domain's list in the first
place, then ATC invalidate gets even simpler too.

The only other uses I can see are of smmu_group->domain, which always
looks to be directly equivalent to to_smmu_domain(iommu_group->domain).
Overall it really looks like the smmu_group abstraction winds up making
the end result more complex than it needs to be.

Robin.

> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> ---
> drivers/iommu/arm-smmu-v3.c | 74 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 74 insertions(+)
>
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 5806a6acc94e..ce8b68fe254b 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -625,6 +625,9 @@ struct arm_smmu_device {
> struct arm_smmu_master_data {
> struct arm_smmu_device *smmu;
> struct arm_smmu_strtab_ent ste;
> +
> + struct device *dev;
> + struct list_head group_head;
> };
>
> /* SMMU private data for an IOMMU domain */
> @@ -650,6 +653,11 @@ struct arm_smmu_domain {
> struct iommu_domain domain;
> };
>
> +struct arm_smmu_group {
> + struct list_head devices;
> + spinlock_t devices_lock;
> +};
> +
> struct arm_smmu_option_prop {
> u32 opt;
> const char *prop;
> @@ -665,6 +673,8 @@ static struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
> return container_of(dom, struct arm_smmu_domain, domain);
> }
>
> +#define to_smmu_group iommu_group_get_iommudata
> +
> static void parse_driver_options(struct arm_smmu_device *smmu)
> {
> int i = 0;
> @@ -1595,6 +1605,30 @@ static int arm_smmu_install_ste_for_dev(struct iommu_fwspec *fwspec)
> return 0;
> }
>
> +static void arm_smmu_group_release(void *smmu_group)
> +{
> + kfree(smmu_group);
> +}
> +
> +static struct arm_smmu_group *arm_smmu_group_alloc(struct iommu_group *group)
> +{
> + struct arm_smmu_group *smmu_group = to_smmu_group(group);
> +
> + if (smmu_group)
> + return smmu_group;
> +
> + smmu_group = kzalloc(sizeof(*smmu_group), GFP_KERNEL);
> + if (!smmu_group)
> + return NULL;
> +
> + INIT_LIST_HEAD(&smmu_group->devices);
> + spin_lock_init(&smmu_group->devices_lock);
> +
> + iommu_group_set_iommudata(group, smmu_group, arm_smmu_group_release);
> +
> + return smmu_group;
> +}
> +
> static void arm_smmu_detach_dev(struct device *dev)
> {
> struct arm_smmu_master_data *master = dev->iommu_fwspec->iommu_priv;
> @@ -1607,7 +1641,9 @@ static void arm_smmu_detach_dev(struct device *dev)
> static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> {
> int ret = 0;
> + struct iommu_group *group;
> struct arm_smmu_device *smmu;
> + struct arm_smmu_group *smmu_group;
> struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
> struct arm_smmu_master_data *master;
> struct arm_smmu_strtab_ent *ste;
> @@ -1619,6 +1655,17 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> smmu = master->smmu;
> ste = &master->ste;
>
> + /*
> + * When adding devices, this is the first occasion we have to create the
> + * smmu_group and attach it to iommu_group.
> + */
> + group = iommu_group_get(dev);
> + smmu_group = arm_smmu_group_alloc(group);
> + if (!smmu_group) {
> + iommu_group_put(group);
> + return -ENOMEM;
> + }
> +
> /* Already attached to a different domain? */
> if (!ste->bypass)
> arm_smmu_detach_dev(dev);
> @@ -1659,6 +1706,9 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>
> out_unlock:
> mutex_unlock(&smmu_domain->init_mutex);
> +
> + iommu_group_put(group);
> +
> return ret;
> }
>
> @@ -1745,7 +1795,9 @@ static struct iommu_ops arm_smmu_ops;
> static int arm_smmu_add_device(struct device *dev)
> {
> int i, ret;
> + unsigned long flags;
> struct arm_smmu_device *smmu;
> + struct arm_smmu_group *smmu_group;
> struct arm_smmu_master_data *master;
> struct iommu_fwspec *fwspec = dev->iommu_fwspec;
> struct iommu_group *group;
> @@ -1769,6 +1821,7 @@ static int arm_smmu_add_device(struct device *dev)
> return -ENOMEM;
>
> master->smmu = smmu;
> + master->dev = dev;
> fwspec->iommu_priv = master;
> }
>
> @@ -1789,6 +1842,12 @@ static int arm_smmu_add_device(struct device *dev)
>
> group = iommu_group_get_for_dev(dev);
> if (!IS_ERR(group)) {
> + smmu_group = to_smmu_group(group);
> +
> + spin_lock_irqsave(&smmu_group->devices_lock, flags);
> + list_add(&master->group_head, &smmu_group->devices);
> + spin_unlock_irqrestore(&smmu_group->devices_lock, flags);
> +
> iommu_group_put(group);
> iommu_device_link(&smmu->iommu, dev);
> }
> @@ -1800,7 +1859,10 @@ static void arm_smmu_remove_device(struct device *dev)
> {
> struct iommu_fwspec *fwspec = dev->iommu_fwspec;
> struct arm_smmu_master_data *master;
> + struct arm_smmu_group *smmu_group;
> struct arm_smmu_device *smmu;
> + struct iommu_group *group;
> + unsigned long flags;
>
> if (!fwspec || fwspec->ops != &arm_smmu_ops)
> return;
> @@ -1809,6 +1871,18 @@ static void arm_smmu_remove_device(struct device *dev)
> smmu = master->smmu;
> if (master && master->ste.valid)
> arm_smmu_detach_dev(dev);
> +
> + if (master) {
> + group = iommu_group_get(dev);
> + smmu_group = to_smmu_group(group);
> +
> + spin_lock_irqsave(&smmu_group->devices_lock, flags);
> + list_del(&master->group_head);
> + spin_unlock_irqrestore(&smmu_group->devices_lock, flags);
> +
> + iommu_group_put(group);
> + }
> +
> iommu_group_remove_device(dev);
> iommu_device_unlink(&smmu->iommu, dev);
> kfree(master);
>