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Merge branch 'for-next/iommu/default-domains' into for-next/iommu/core

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Support for changing the default domain type for singleton IOMMU groups
via sysfs when the constituent device is not already bound to a device
driver.

* for-next/iommu/default-domains:
  iommu: Fix htmldocs warnings in sysfs-kernel-iommu_groups
  iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file
  iommu: Take lock before reading iommu group default domain type
  iommu: Add support to change default domain of an iommu group
  iommu: Move def_domain type check for untrusted device into core
This commit is contained in:
Will Deacon 2020-12-08 14:56:53 +00:00
commit 33f974dbaa
3 changed files with 268 additions and 17 deletions
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30
Documentation/ABI/testing/sysfs-kernel-iommu_groups
View File

@ -33,3 +33,33 @@ Description: In case an RMRR is used only by graphics or USB devices
it is now exposed as "direct-relaxable" instead of "direct".
In device assignment use case, for instance, those RMRR
are considered to be relaxable and safe.
What: /sys/kernel/iommu_groups/<grp_id>/type
Date: November 2020
KernelVersion: v5.11
Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default
domain in use by iommu for this group. See include/linux/iommu.h
for possible read values. A privileged user could request kernel to
change the group type by writing to this file. Valid write values:
======== ======================================================
DMA All the DMA transactions from the device in this group
are translated by the iommu.
identity All the DMA transactions from the device in this group
are not translated by the iommu.
auto Change to the type the device was booted with.
======== ======================================================
The default domain type of a group may be modified only when
- The group has only one device.
- The device in the group is not bound to any device driver.
So, the users must unbind the appropriate driver before
changing the default domain type.
Unbinding a device driver will take away the driver's control
over the device and if done on devices that host root file
system could lead to catastrophic effects (the users might
need to reboot the machine to get it to normal state). So, it's
expected that the users understand what they're doing.

7
drivers/iommu/intel/iommu.c
View File

@ -2916,13 +2916,6 @@ static int device_def_domain_type(struct device *dev)
if (dev_is_pci(dev)) {
struct pci_dev *pdev = to_pci_dev(dev);
/*
* Prevent any device marked as untrusted from getting
* placed into the statically identity mapping domain.
*/
if (pdev->untrusted)
return IOMMU_DOMAIN_DMA;
if ((iommu_identity_mapping & IDENTMAP_AZALIA) && IS_AZALIA(pdev))
return IOMMU_DOMAIN_IDENTITY;

248
drivers/iommu/iommu.c
View File

@ -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 = \
@ -499,6 +501,7 @@ static ssize_t iommu_group_show_type(struct iommu_group *group,
{
char *type = "unknown\n";
mutex_lock(&group->mutex);
if (group->default_domain) {
switch (group->default_domain->type) {
case IOMMU_DOMAIN_BLOCKED:
@ -515,6 +518,7 @@ static ssize_t iommu_group_show_type(struct iommu_group *group,
break;
}
}
mutex_unlock(&group->mutex);
strcpy(buf, type);
return strlen(type);
@ -525,7 +529,8 @@ 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)
{
@ -1460,12 +1465,14 @@ EXPORT_SYMBOL_GPL(fsl_mc_device_group);
static int iommu_get_def_domain_type(struct device *dev)
{
const struct iommu_ops *ops = dev->bus->iommu_ops;
unsigned int type = 0;
if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted)
return IOMMU_DOMAIN_DMA;
if (ops->def_domain_type)
type = ops->def_domain_type(dev);
return ops->def_domain_type(dev);
return (type == 0) ? iommu_def_domain_type : type;
return 0;
}
static int iommu_group_alloc_default_domain(struct bus_type *bus,
@ -1507,7 +1514,7 @@ static int iommu_alloc_default_domain(struct iommu_group *group,
if (group->default_domain)
return 0;
type = iommu_get_def_domain_type(dev);
type = iommu_get_def_domain_type(dev) ? : iommu_def_domain_type;
return iommu_group_alloc_default_domain(dev->bus, group, type);
}
@ -1645,12 +1652,8 @@ struct __group_domain_type {
static int probe_get_default_domain_type(struct device *dev, void *data)
{
const struct iommu_ops *ops = dev->bus->iommu_ops;
struct __group_domain_type *gtype = data;
unsigned int type = 0;
if (ops->def_domain_type)
type = ops->def_domain_type(dev);
unsigned int type = iommu_get_def_domain_type(dev);
if (type) {
if (gtype->type && gtype->type != type) {
@ -3029,3 +3032,228 @@ 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;
}