diff options
| -rw-r--r-- | drivers/iommu/iommu.c | 230 |
1 files changed, 229 insertions, 1 deletions
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index 9a5ec1c7a8ac..b326389deea4 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -93,6 +93,8 @@ static void __iommu_detach_group(struct iommu_domain *domain, static int iommu_create_device_direct_mappings(struct iommu_group *group, struct device *dev); static struct iommu_group *iommu_group_get_for_dev(struct device *dev); +static ssize_t iommu_group_store_type(struct iommu_group *group, + const char *buf, size_t count); #define IOMMU_GROUP_ATTR(_name, _mode, _show, _store) \ struct iommu_group_attribute iommu_group_attr_##_name = \ @@ -525,7 +527,8 @@ static IOMMU_GROUP_ATTR(name, S_IRUGO, iommu_group_show_name, NULL); static IOMMU_GROUP_ATTR(reserved_regions, 0444, iommu_group_show_resv_regions, NULL); -static IOMMU_GROUP_ATTR(type, 0444, iommu_group_show_type, NULL); +static IOMMU_GROUP_ATTR(type, 0644, iommu_group_show_type, + iommu_group_store_type); static void iommu_group_release(struct kobject *kobj) { @@ -3027,3 +3030,228 @@ u32 iommu_sva_get_pasid(struct iommu_sva *handle) return ops->sva_get_pasid(handle); } EXPORT_SYMBOL_GPL(iommu_sva_get_pasid); + +/* + * Changes the default domain of an iommu group that has *only* one device + * + * @group: The group for which the default domain should be changed + * @prev_dev: The device in the group (this is used to make sure that the device + * hasn't changed after the caller has called this function) + * @type: The type of the new default domain that gets associated with the group + * + * Returns 0 on success and error code on failure + * + * Note: + * 1. Presently, this function is called only when user requests to change the + * group's default domain type through /sys/kernel/iommu_groups/<grp_id>/type + * Please take a closer look if intended to use for other purposes. + */ +static int iommu_change_dev_def_domain(struct iommu_group *group, + struct device *prev_dev, int type) +{ + struct iommu_domain *prev_dom; + struct group_device *grp_dev; + int ret, dev_def_dom; + struct device *dev; + + if (!group) + return -EINVAL; + + mutex_lock(&group->mutex); + + if (group->default_domain != group->domain) { + dev_err_ratelimited(prev_dev, "Group not assigned to default domain\n"); + ret = -EBUSY; + goto out; + } + + /* + * iommu group wasn't locked while acquiring device lock in + * iommu_group_store_type(). So, make sure that the device count hasn't + * changed while acquiring device lock. + * + * Changing default domain of an iommu group with two or more devices + * isn't supported because there could be a potential deadlock. Consider + * the following scenario. T1 is trying to acquire device locks of all + * the devices in the group and before it could acquire all of them, + * there could be another thread T2 (from different sub-system and use + * case) that has already acquired some of the device locks and might be + * waiting for T1 to release other device locks. + */ + if (iommu_group_device_count(group) != 1) { + dev_err_ratelimited(prev_dev, "Cannot change default domain: Group has more than one device\n"); + ret = -EINVAL; + goto out; + } + + /* Since group has only one device */ + grp_dev = list_first_entry(&group->devices, struct group_device, list); + dev = grp_dev->dev; + + if (prev_dev != dev) { + dev_err_ratelimited(prev_dev, "Cannot change default domain: Device has been changed\n"); + ret = -EBUSY; + goto out; + } + + prev_dom = group->default_domain; + if (!prev_dom) { + ret = -EINVAL; + goto out; + } + + dev_def_dom = iommu_get_def_domain_type(dev); + if (!type) { + /* + * If the user hasn't requested any specific type of domain and + * if the device supports both the domains, then default to the + * domain the device was booted with + */ + type = dev_def_dom ? : iommu_def_domain_type; + } else if (dev_def_dom && type != dev_def_dom) { + dev_err_ratelimited(prev_dev, "Device cannot be in %s domain\n", + iommu_domain_type_str(type)); + ret = -EINVAL; + goto out; + } + + /* + * Switch to a new domain only if the requested domain type is different + * from the existing default domain type + */ + if (prev_dom->type == type) { + ret = 0; + goto out; + } + + /* Sets group->default_domain to the newly allocated domain */ + ret = iommu_group_alloc_default_domain(dev->bus, group, type); + if (ret) + goto out; + + ret = iommu_create_device_direct_mappings(group, dev); + if (ret) + goto free_new_domain; + + ret = __iommu_attach_device(group->default_domain, dev); + if (ret) + goto free_new_domain; + + group->domain = group->default_domain; + + /* + * Release the mutex here because ops->probe_finalize() call-back of + * some vendor IOMMU drivers calls arm_iommu_attach_device() which + * in-turn might call back into IOMMU core code, where it tries to take + * group->mutex, resulting in a deadlock. + */ + mutex_unlock(&group->mutex); + + /* Make sure dma_ops is appropriatley set */ + iommu_group_do_probe_finalize(dev, group->default_domain); + iommu_domain_free(prev_dom); + return 0; + +free_new_domain: + iommu_domain_free(group->default_domain); + group->default_domain = prev_dom; + group->domain = prev_dom; + +out: + mutex_unlock(&group->mutex); + + return ret; +} + +/* + * Changing the default domain through sysfs requires the users to ubind the + * drivers from the devices in the iommu group. Return failure if this doesn't + * meet. + * + * We need to consider the race between this and the device release path. + * device_lock(dev) is used here to guarantee that the device release path + * will not be entered at the same time. + */ +static ssize_t iommu_group_store_type(struct iommu_group *group, + const char *buf, size_t count) +{ + struct group_device *grp_dev; + struct device *dev; + int ret, req_type; + + if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO)) + return -EACCES; + + if (WARN_ON(!group)) + return -EINVAL; + + if (sysfs_streq(buf, "identity")) + req_type = IOMMU_DOMAIN_IDENTITY; + else if (sysfs_streq(buf, "DMA")) + req_type = IOMMU_DOMAIN_DMA; + else if (sysfs_streq(buf, "auto")) + req_type = 0; + else + return -EINVAL; + + /* + * Lock/Unlock the group mutex here before device lock to + * 1. Make sure that the iommu group has only one device (this is a + * prerequisite for step 2) + * 2. Get struct *dev which is needed to lock device + */ + mutex_lock(&group->mutex); + if (iommu_group_device_count(group) != 1) { + mutex_unlock(&group->mutex); + pr_err_ratelimited("Cannot change default domain: Group has more than one device\n"); + return -EINVAL; + } + + /* Since group has only one device */ + grp_dev = list_first_entry(&group->devices, struct group_device, list); + dev = grp_dev->dev; + get_device(dev); + + /* + * Don't hold the group mutex because taking group mutex first and then + * the device lock could potentially cause a deadlock as below. Assume + * two threads T1 and T2. T1 is trying to change default domain of an + * iommu group and T2 is trying to hot unplug a device or release [1] VF + * of a PCIe device which is in the same iommu group. T1 takes group + * mutex and before it could take device lock assume T2 has taken device + * lock and is yet to take group mutex. Now, both the threads will be + * waiting for the other thread to release lock. Below, lock order was + * suggested. + * device_lock(dev); + * mutex_lock(&group->mutex); + * iommu_change_dev_def_domain(); + * mutex_unlock(&group->mutex); + * device_unlock(dev); + * + * [1] Typical device release path + * device_lock() from device/driver core code + * -> bus_notifier() + * -> iommu_bus_notifier() + * -> iommu_release_device() + * -> ops->release_device() vendor driver calls back iommu core code + * -> mutex_lock() from iommu core code + */ + mutex_unlock(&group->mutex); + + /* Check if the device in the group still has a driver bound to it */ + device_lock(dev); + if (device_is_bound(dev)) { + pr_err_ratelimited("Device is still bound to driver\n"); + ret = -EBUSY; + goto out; + } + + ret = iommu_change_dev_def_domain(group, dev, req_type); + ret = ret ?: count; + +out: + device_unlock(dev); + put_device(dev); + + return ret; +} |