[RFC 13/20] iommu: Extend iommu_at[de]tach_device() for multiple devices group

Liu Yi L
2021-09-19T06:43:02Z

From: Lu Baolu <baolu.lu@linux.intel.com>

These two helpers could be used when 1) the iommu group is singleton,
or 2) the upper layer has put the iommu group into the secure state by
calling iommu_device_init_user_dma().

As we want the iommufd design to be a device-centric model, we want to
remove any group knowledge in iommufd. Given that we already have
iommu_at[de]tach_device() interface, we could extend it for iommufd
simply by doing below:

- first device in a group does group attach;
- last device in a group does group detach.

as long as the group has been put into the secure context.

The commit <426a273834eae> ("iommu: Limit iommu_attach/detach_device to
device with their own group") deliberately restricts the two interfaces
to single-device group. To avoid the conflict with existing usages, we
keep this policy and put the new extension only when the group has been
marked for user_dma.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
drivers/iommu/iommu.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index bffd84e978fb..b6178997aef1 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -47,6 +47,7 @@ struct iommu_group {
struct list_head entry;
unsigned long user_dma_owner_id;
refcount_t owner_cnt;
+ refcount_t attach_cnt;
};

struct group_device {
@@ -1994,7 +1995,7 @@ static int __iommu_attach_device(struct iommu_domain *domain,
int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
{
struct iommu_group *group;
- int ret;
+ int ret = 0;

group = iommu_group_get(dev);
if (!group)
@@ -2005,11 +2006,23 @@ int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
* change while we are attaching
*/
mutex_lock(&group->mutex);
- ret = -EINVAL;
- if (iommu_group_device_count(group) != 1)
+ if (group->user_dma_owner_id) {
+ if (group->domain) {
+ if (group->domain != domain)
+ ret = -EBUSY;
+ else
+ refcount_inc(&group->attach_cnt);
+
+ goto out_unlock;
+ }
+ } else if (iommu_group_device_count(group) != 1) {
+ ret = -EINVAL;
goto out_unlock;
+ }

ret = __iommu_attach_group(domain, group);
+ if (!ret && group->user_dma_owner_id)
+ refcount_set(&group->attach_cnt, 1);

out_unlock:
mutex_unlock(&group->mutex);
@@ -2261,7 +2274,10 @@ void iommu_detach_device(struct iommu_domain *domain, struct device *dev)
return;

mutex_lock(&group->mutex);
- if (iommu_group_device_count(group) != 1) {
+ if (group->user_dma_owner_id) {
+ if (!refcount_dec_and_test(&group->attach_cnt))
+ goto out_unlock;
+ } else if (iommu_group_device_count(group) != 1) {
WARN_ON(1);
goto out_unlock;
}
@@ -3368,6 +3384,7 @@ static int iommu_group_init_user_dma(struct iommu_group *group,

group->user_dma_owner_id = owner;
refcount_set(&group->owner_cnt, 1);
+ refcount_set(&group->attach_cnt, 0);

/* default domain is unsafe for user-initiated dma */
if (group->domain == group->default_domain)
--
2.25.1