path: root/drivers/iommu/iommufd/device.c

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2021-2022, NVIDIA CORPORATION & AFFILIATES
 */
#include <linux/iommufd.h>
#include <linux/slab.h>
#include <linux/iommu.h>
#include <uapi/linux/iommufd.h>
#include "../iommu-priv.h"

#include "io_pagetable.h"
#include "iommufd_private.h"

static bool allow_unsafe_interrupts;
module_param(allow_unsafe_interrupts, bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(
	allow_unsafe_interrupts,
	"Allow IOMMUFD to bind to devices even if the platform cannot isolate "
	"the MSI interrupt window. Enabling this is a security weakness.");

static void iommufd_group_release(struct kref *kref)
{
	struct iommufd_group *igroup =
		container_of(kref, struct iommufd_group, ref);

	WARN_ON(igroup->hwpt || !list_empty(&igroup->device_list));

	xa_cmpxchg(&igroup->ictx->groups, iommu_group_id(igroup->group), igroup,
		   NULL, GFP_KERNEL);
	iommu_group_put(igroup->group);
	mutex_destroy(&igroup->lock);
	kfree(igroup);
}

static void iommufd_put_group(struct iommufd_group *group)
{
	kref_put(&group->ref, iommufd_group_release);
}

static bool iommufd_group_try_get(struct iommufd_group *igroup,
				  struct iommu_group *group)
{
	if (!igroup)
		return false;
	/*
	 * group ID's cannot be re-used until the group is put back which does
	 * not happen if we could get an igroup pointer under the xa_lock.
	 */
	if (WARN_ON(igroup->group != group))
		return false;
	return kref_get_unless_zero(&igroup->ref);
}

/*
 * iommufd needs to store some more data for each iommu_group, we keep a
 * parallel xarray indexed by iommu_group id to hold this instead of putting it
 * in the core structure. To keep things simple the iommufd_group memory is
 * unique within the iommufd_ctx. This makes it easy to check there are no
 * memory leaks.
 */
static struct iommufd_group *iommufd_get_group(struct iommufd_ctx *ictx,
					       struct device *dev)
{
	struct iommufd_group *new_igroup;
	struct iommufd_group *cur_igroup;
	struct iommufd_group *igroup;
	struct iommu_group *group;
	unsigned int id;

	group = iommu_group_get(dev);
	if (!group)
		return ERR_PTR(-ENODEV);

	id = iommu_group_id(group);

	xa_lock(&ictx->groups);
	igroup = xa_load(&ictx->groups, id);
	if (iommufd_group_try_get(igroup, group)) {
		xa_unlock(&ictx->groups);
		iommu_group_put(group);
		return igroup;
	}
	xa_unlock(&ictx->groups);

	new_igroup = kzalloc(sizeof(*new_igroup), GFP_KERNEL);
	if (!new_igroup) {
		iommu_group_put(group);
		return ERR_PTR(-ENOMEM);
	}

	kref_init(&new_igroup->ref);
	mutex_init(&new_igroup->lock);
	INIT_LIST_HEAD(&new_igroup->device_list);
	new_igroup->sw_msi_start = PHYS_ADDR_MAX;
	/* group reference moves into new_igroup */
	new_igroup->group = group;

	/*
	 * The ictx is not additionally refcounted here becase all objects using
	 * an igroup must put it before their destroy completes.
	 */
	new_igroup->ictx = ictx;

	/*
	 * We dropped the lock so igroup is invalid. NULL is a safe and likely
	 * value to assume for the xa_cmpxchg algorithm.
	 */
	cur_igroup = NULL;
	xa_lock(&ictx->groups);
	while (true) {
		igroup = __xa_cmpxchg(&ictx->groups, id, cur_igroup, new_igroup,
				      GFP_KERNEL);
		if (xa_is_err(igroup)) {
			xa_unlock(&ictx->groups);
			iommufd_put_group(new_igroup);
			return ERR_PTR(xa_err(igroup));
		}

		/* new_group was successfully installed */
		if (cur_igroup == igroup) {
			xa_unlock(&ictx->groups);
			return new_igroup;
		}

		/* Check again if the current group is any good */
		if (iommufd_group_try_get(igroup, group)) {
			xa_unlock(&ictx->groups);
			iommufd_put_group(new_igroup);
			return igroup;
		}
		cur_igroup = igroup;
	}
}

void iommufd_device_destroy(struct iommufd_object *obj)
{
	struct iommufd_device *idev =
		container_of(obj, struct iommufd_device, obj);

	iommu_device_release_dma_owner(idev->dev);
	iommufd_put_group(idev->igroup);
	if (!iommufd_selftest_is_mock_dev(idev->dev))
		iommufd_ctx_put(idev->ictx);
}

/**
 * iommufd_device_bind - Bind a physical device to an iommu fd
 * @ictx: iommufd file descriptor
 * @dev: Pointer to a physical device struct
 * @id: Output ID number to return to userspace for this device
 *
 * A successful bind establishes an ownership over the device and returns
 * struct iommufd_device pointer, otherwise returns error pointer.
 *
 * A driver using this API must set driver_managed_dma and must not touch
 * the device until this routine succeeds and establishes ownership.
 *
 * Binding a PCI device places the entire RID under iommufd control.
 *
 * The caller must undo this with iommufd_device_unbind()
 */
struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
					   struct device *dev, u32 *id)
{
	struct iommufd_device *idev;
	struct iommufd_group *igroup;
	int rc;

	/*
	 * iommufd always sets IOMMU_CACHE because we offer no way for userspace
	 * to restore cache coherency.
	 */
	if (!device_iommu_capable(dev, IOMMU_CAP_CACHE_COHERENCY))
		return ERR_PTR(-EINVAL);

	igroup = iommufd_get_group(ictx, dev);
	if (IS_ERR(igroup))
		return ERR_CAST(igroup);

	/*
	 * For historical compat with VFIO the insecure interrupt path is
	 * allowed if the module parameter is set. Secure/Isolated means that a
	 * MemWr operation from the device (eg a simple DMA) cannot trigger an
	 * interrupt outside this iommufd context.
	 */
	if (!iommufd_selftest_is_mock_dev(dev) &&
	    !iommu_group_has_isolated_msi(igroup->group)) {
		if (!allow_unsafe_interrupts) {
			rc = -EPERM;
			goto out_group_put;
		}

		dev_warn(
			dev,
			"MSI interrupts are not secure, they cannot be isolated by the platform. "
			"Check that platform features like interrupt remapping are enabled. "
			"Use the \"allow_unsafe_interrupts\" module parameter to override\n");
	}

	rc = iommu_device_claim_dma_owner(dev, ictx);
	if (rc)
		goto out_group_put;

	idev = iommufd_object_alloc(ictx, idev, IOMMUFD_OBJ_DEVICE);
	if (IS_ERR(idev)) {
		rc = PTR_ERR(idev);
		goto out_release_owner;
	}
	idev->ictx = ictx;
	if (!iommufd_selftest_is_mock_dev(dev))
		iommufd_ctx_get(ictx);
	idev->dev = dev;
	idev->enforce_cache_coherency =
		device_iommu_capable(dev, IOMMU_CAP_ENFORCE_CACHE_COHERENCY);
	/* The calling driver is a user until iommufd_device_unbind() */
	refcount_inc(&idev->obj.users);
	/* igroup refcount moves into iommufd_device */
	idev->igroup = igroup;

	/*
	 * If the caller fails after this success it must call
	 * iommufd_unbind_device() which is safe since we hold this refcount.
	 * This also means the device is a leaf in the graph and no other object
	 * can take a reference on it.
	 */
	iommufd_object_finalize(ictx, &idev->obj);
	*id = idev->obj.id;
	return idev;

out_release_owner:
	iommu_device_release_dma_owner(dev);
out_group_put:
	iommufd_put_group(igroup);
	return ERR_PTR(rc);
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_bind, IOMMUFD);

/**
 * iommufd_ctx_has_group - True if any device within the group is bound
 *                         to the ictx
 * @ictx: iommufd file descriptor
 * @group: Pointer to a physical iommu_group struct
 *
 * True if any device within the group has been bound to this ictx, ex. via
 * iommufd_device_bind(), therefore implying ictx ownership of the group.
 */
bool iommufd_ctx_has_group(struct iommufd_ctx *ictx, struct iommu_group *group)
{
	struct iommufd_object *obj;
	unsigned long index;

	if (!ictx || !group)
		return false;

	xa_lock(&ictx->objects);
	xa_for_each(&ictx->objects, index, obj) {
		if (obj->type == IOMMUFD_OBJ_DEVICE &&
		    container_of(obj, struct iommufd_device, obj)
				    ->igroup->group == group) {
			xa_unlock(&ictx->objects);
			return true;
		}
	}
	xa_unlock(&ictx->objects);
	return false;
}
EXPORT_SYMBOL_NS_GPL(iommufd_ctx_has_group, IOMMUFD);

/**
 * iommufd_device_unbind - Undo iommufd_device_bind()
 * @idev: Device returned by iommufd_device_bind()
 *
 * Release the device from iommufd control. The DMA ownership will return back
 * to unowned with DMA controlled by the DMA API. This invalidates the
 * iommufd_device pointer, other APIs that consume it must not be called
 * concurrently.
 */
void iommufd_device_unbind(struct iommufd_device *idev)
{
	iommufd_object_destroy_user(idev->ictx, &idev->obj);
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_unbind, IOMMUFD);

struct iommufd_ctx *iommufd_device_to_ictx(struct iommufd_device *idev)
{
	return idev->ictx;
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_to_ictx, IOMMUFD);

u32 iommufd_device_to_id(struct iommufd_device *idev)
{
	return idev->obj.id;
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_to_id, IOMMUFD);

static int iommufd_group_setup_msi(struct iommufd_group *igroup,
				   struct iommufd_hwpt_paging *hwpt_paging)
{
	phys_addr_t sw_msi_start = igroup->sw_msi_start;
	int rc;

	/*
	 * If the IOMMU driver gives a IOMMU_RESV_SW_MSI then it is asking us to
	 * call iommu_get_msi_cookie() on its behalf. This is necessary to setup
	 * the MSI window so iommu_dma_prepare_msi() can install pages into our
	 * domain after request_irq(). If it is not done interrupts will not
	 * work on this domain.
	 *
	 * FIXME: This is conceptually broken for iommufd since we want to allow
	 * userspace to change the domains, eg switch from an identity IOAS to a
	 * DMA IOAS. There is currently no way to create a MSI window that
	 * matches what the IRQ layer actually expects in a newly created
	 * domain.
	 */
	if (sw_msi_start != PHYS_ADDR_MAX && !hwpt_paging->msi_cookie) {
		rc = iommu_get_msi_cookie(hwpt_paging->common.domain,
					  sw_msi_start);
		if (rc)
			return rc;

		/*
		 * iommu_get_msi_cookie() can only be called once per domain,
		 * it returns -EBUSY on later calls.
		 */
		hwpt_paging->msi_cookie = true;
	}
	return 0;
}

static int iommufd_hwpt_paging_attach(struct iommufd_hwpt_paging *hwpt_paging,
				      struct iommufd_device *idev)
{
	int rc;

	lockdep_assert_held(&idev->igroup->lock);

	rc = iopt_table_enforce_dev_resv_regions(&hwpt_paging->ioas->iopt,
						 idev->dev,
						 &idev->igroup->sw_msi_start);
	if (rc)
		return rc;

	if (list_empty(&idev->igroup->device_list)) {
		rc = iommufd_group_setup_msi(idev->igroup, hwpt_paging);
		if (rc) {
			iopt_remove_reserved_iova(&hwpt_paging->ioas->iopt,
						  idev->dev);
			return rc;
		}
	}
	return 0;
}

int iommufd_hw_pagetable_attach(struct iommufd_hw_pagetable *hwpt,
				struct iommufd_device *idev)
{
	int rc;

	mutex_lock(&idev->igroup->lock);

	if (idev->igroup->hwpt != NULL && idev->igroup->hwpt != hwpt) {
		rc = -EINVAL;
		goto err_unlock;
	}

	if (hwpt_is_paging(hwpt)) {
		rc = iommufd_hwpt_paging_attach(to_hwpt_paging(hwpt), idev);
		if (rc)
			goto err_unlock;
	}

	/*
	 * Only attach to the group once for the first device that is in the
	 * group. All the other devices will follow this attachment. The user
	 * should attach every device individually to the hwpt as the per-device
	 * reserved regions are only updated during individual device
	 * attachment.
	 */
	if (list_empty(&idev->igroup->device_list)) {
		rc = iommu_attach_group(hwpt->domain, idev->igroup->group);
		if (rc)
			goto err_unresv;
		idev->igroup->hwpt = hwpt;
	}
	refcount_inc(&hwpt->obj.users);
	list_add_tail(&idev->group_item, &idev->igroup->device_list);
	mutex_unlock(&idev->igroup->lock);
	return 0;
err_unresv:
	if (hwpt_is_paging(hwpt))
		iopt_remove_reserved_iova(&to_hwpt_paging(hwpt)->ioas->iopt,
					  idev->dev);
err_unlock:
	mutex_unlock(&idev->igroup->lock);
	return rc;
}

struct iommufd_hw_pagetable *
iommufd_hw_pagetable_detach(struct iommufd_device *idev)
{
	struct iommufd_hw_pagetable *hwpt = idev->igroup->hwpt;

	mutex_lock(&idev->igroup->lock);
	list_del(&idev->group_item);
	if (list_empty(&idev->igroup->device_list)) {
		iommu_detach_group(hwpt->domain, idev->igroup->group);
		idev->igroup->hwpt = NULL;
	}
	if (hwpt_is_paging(hwpt))
		iopt_remove_reserved_iova(&to_hwpt_paging(hwpt)->ioas->iopt,
					  idev->dev);
	mutex_unlock(&idev->igroup->lock);

	/* Caller must destroy hwpt */
	return hwpt;
}

static struct iommufd_hw_pagetable *
iommufd_device_do_attach(struct iommufd_device *idev,
			 struct iommufd_hw_pagetable *hwpt)
{
	int rc;

	rc = iommufd_hw_pagetable_attach(hwpt, idev);
	if (rc)
		return ERR_PTR(rc);
	return NULL;
}

static void
iommufd_group_remove_reserved_iova(struct iommufd_group *igroup,
				   struct iommufd_hwpt_paging *hwpt_paging)
{
	struct iommufd_device *cur;

	lockdep_assert_held(&igroup->lock);

	list_for_each_entry(cur, &igroup->device_list, group_item)
		iopt_remove_reserved_iova(&hwpt_paging->ioas->iopt, cur->dev);
}

static int
iommufd_group_do_replace_paging(struct iommufd_group *igroup,
				struct iommufd_hwpt_paging *hwpt_paging)
{
	struct iommufd_hw_pagetable *old_hwpt = igroup->hwpt;
	struct iommufd_device *cur;
	int rc;

	lockdep_assert_held(&igroup->lock);

	if (!hwpt_is_paging(old_hwpt) ||
	    hwpt_paging->ioas != to_hwpt_paging(old_hwpt)->ioas) {
		list_for_each_entry(cur, &igroup->device_list, group_item) {
			rc = iopt_table_enforce_dev_resv_regions(
				&hwpt_paging->ioas->iopt, cur->dev, NULL);
			if (rc)
				goto err_unresv;
		}
	}

	rc = iommufd_group_setup_msi(igroup, hwpt_paging);
	if (rc)
		goto err_unresv;
	return 0;

err_unresv:
	iommufd_group_remove_reserved_iova(igroup, hwpt_paging);
	return rc;
}

static struct iommufd_hw_pagetable *
iommufd_device_do_replace(struct iommufd_device *idev,
			  struct iommufd_hw_pagetable *hwpt)
{
	struct iommufd_group *igroup = idev->igroup;
	struct iommufd_hw_pagetable *old_hwpt;
	unsigned int num_devices;
	int rc;

	mutex_lock(&idev->igroup->lock);

	if (igroup->hwpt == NULL) {
		rc = -EINVAL;
		goto err_unlock;
	}

	if (hwpt == igroup->hwpt) {
		mutex_unlock(&idev->igroup->lock);
		return NULL;
	}

	old_hwpt = igroup->hwpt;
	if (hwpt_is_paging(hwpt)) {
		rc = iommufd_group_do_replace_paging(igroup,
						     to_hwpt_paging(hwpt));
		if (rc)
			goto err_unlock;
	}

	rc = iommu_group_replace_domain(igroup->group, hwpt->domain);
	if (rc)
		goto err_unresv;

	if (hwpt_is_paging(old_hwpt) &&
	    (!hwpt_is_paging(hwpt) ||
	     to_hwpt_paging(hwpt)->ioas != to_hwpt_paging(old_hwpt)->ioas))
		iommufd_group_remove_reserved_iova(igroup,
						   to_hwpt_paging(old_hwpt));

	igroup->hwpt = hwpt;

	num_devices = list_count_nodes(&igroup->device_list);
	/*
	 * Move the refcounts held by the device_list to the new hwpt. Retain a
	 * refcount for this thread as the caller will free it.
	 */
	refcount_add(num_devices, &hwpt->obj.users);
	if (num_devices > 1)
		WARN_ON(refcount_sub_and_test(num_devices - 1,
					      &old_hwpt->obj.users));
	mutex_unlock(&idev->igroup->lock);

	/* Caller must destroy old_hwpt */
	return old_hwpt;
err_unresv:
	if (hwpt_is_paging(hwpt))
		iommufd_group_remove_reserved_iova(igroup,
						   to_hwpt_paging(old_hwpt));
err_unlock:
	mutex_unlock(&idev->igroup->lock);
	return ERR_PTR(rc);
}

typedef struct iommufd_hw_pagetable *(*attach_fn)(
	struct iommufd_device *idev, struct iommufd_hw_pagetable *hwpt);

/*
 * When automatically managing the domains we search for a compatible domain in
 * the iopt and if one is found use it, otherwise create a new domain.
 * Automatic domain selection will never pick a manually created domain.
 */
static struct iommufd_hw_pagetable *
iommufd_device_auto_get_domain(struct iommufd_device *idev,
			       struct iommufd_ioas *ioas, u32 *pt_id,
			       attach_fn do_attach)
{
	/*
	 * iommufd_hw_pagetable_attach() is called by
	 * iommufd_hw_pagetable_alloc() in immediate attachment mode, same as
	 * iommufd_device_do_attach(). So if we are in this mode then we prefer
	 * to use the immediate_attach path as it supports drivers that can't
	 * directly allocate a domain.
	 */
	bool immediate_attach = do_attach == iommufd_device_do_attach;
	struct iommufd_hw_pagetable *destroy_hwpt;
	struct iommufd_hwpt_paging *hwpt_paging;
	struct iommufd_hw_pagetable *hwpt;

	/*
	 * There is no differentiation when domains are allocated, so any domain
	 * that is willing to attach to the device is interchangeable with any
	 * other.
	 */
	mutex_lock(&ioas->mutex);
	list_for_each_entry(hwpt_paging, &ioas->hwpt_list, hwpt_item) {
		if (!hwpt_paging->auto_domain)
			continue;

		hwpt = &hwpt_paging->common;
		if (!iommufd_lock_obj(&hwpt->obj))
			continue;
		destroy_hwpt = (*do_attach)(idev, hwpt);
		if (IS_ERR(destroy_hwpt)) {
			iommufd_put_object(&hwpt->obj);
			/*
			 * -EINVAL means the domain is incompatible with the
			 * device. Other error codes should propagate to
			 * userspace as failure. Success means the domain is
			 * attached.
			 */
			if (PTR_ERR(destroy_hwpt) == -EINVAL)
				continue;
			goto out_unlock;
		}
		*pt_id = hwpt->obj.id;
		iommufd_put_object(&hwpt->obj);
		goto out_unlock;
	}

	hwpt_paging = iommufd_hwpt_paging_alloc(idev->ictx, ioas, idev, 0,
						immediate_attach, NULL);
	if (IS_ERR(hwpt_paging)) {
		destroy_hwpt = ERR_CAST(hwpt_paging);
		goto out_unlock;
	}
	hwpt = &hwpt_paging->common;

	if (!immediate_attach) {
		destroy_hwpt = (*do_attach)(idev, hwpt);
		if (IS_ERR(destroy_hwpt))
			goto out_abort;
	} else {
		destroy_hwpt = NULL;
	}

	hwpt_paging->auto_domain = true;
	*pt_id = hwpt->obj.id;

	iommufd_object_finalize(idev->ictx, &hwpt->obj);
	mutex_unlock(&ioas->mutex);
	return destroy_hwpt;

out_abort:
	iommufd_object_abort_and_destroy(idev->ictx, &hwpt->obj);
out_unlock:
	mutex_unlock(&ioas->mutex);
	return destroy_hwpt;
}

static int iommufd_device_change_pt(struct iommufd_device *idev, u32 *pt_id,
				    attach_fn do_attach)
{
	struct iommufd_hw_pagetable *destroy_hwpt;
	struct iommufd_object *pt_obj;

	pt_obj = iommufd_get_object(idev->ictx, *pt_id, IOMMUFD_OBJ_ANY);
	if (IS_ERR(pt_obj))
		return PTR_ERR(pt_obj);

	switch (pt_obj->type) {
	case IOMMUFD_OBJ_HWPT_NESTED:
	case IOMMUFD_OBJ_HWPT_PAGING: {
		struct iommufd_hw_pagetable *hwpt =
			container_of(pt_obj, struct iommufd_hw_pagetable, obj);

		destroy_hwpt = (*do_attach)(idev, hwpt);
		if (IS_ERR(destroy_hwpt))
			goto out_put_pt_obj;
		break;
	}
	case IOMMUFD_OBJ_IOAS: {
		struct iommufd_ioas *ioas =
			container_of(pt_obj, struct iommufd_ioas, obj);

		destroy_hwpt = iommufd_device_auto_get_domain(idev, ioas, pt_id,
							      do_attach);
		if (IS_ERR(destroy_hwpt))
			goto out_put_pt_obj;
		break;
	}
	default:
		destroy_hwpt = ERR_PTR(-EINVAL);
		goto out_put_pt_obj;
	}
	iommufd_put_object(pt_obj);

	/* This destruction has to be after we unlock everything */
	if (destroy_hwpt)
		iommufd_hw_pagetable_put(idev->ictx, destroy_hwpt);
	return 0;

out_put_pt_obj:
	iommufd_put_object(pt_obj);
	return PTR_ERR(destroy_hwpt);
}

/**
 * iommufd_device_attach - Connect a device to an iommu_domain
 * @idev: device to attach
 * @pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HWPT_PAGING
 *         Output the IOMMUFD_OBJ_HWPT_PAGING ID
 *
 * This connects the device to an iommu_domain, either automatically or manually
 * selected. Once this completes the device could do DMA.
 *
 * The caller should return the resulting pt_id back to userspace.
 * This function is undone by calling iommufd_device_detach().
 */
int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id)
{
	int rc;

	rc = iommufd_device_change_pt(idev, pt_id, &iommufd_device_do_attach);
	if (rc)
		return rc;

	/*
	 * Pairs with iommufd_device_detach() - catches caller bugs attempting
	 * to destroy a device with an attachment.
	 */
	refcount_inc(&idev->obj.users);
	return 0;
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_attach, IOMMUFD);

/**
 * iommufd_device_replace - Change the device's iommu_domain
 * @idev: device to change
 * @pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HWPT_PAGING
 *         Output the IOMMUFD_OBJ_HWPT_PAGING ID
 *
 * This is the same as::
 *
 *   iommufd_device_detach();
 *   iommufd_device_attach();
 *
 * If it fails then no change is made to the attachment. The iommu driver may
 * implement this so there is no disruption in translation. This can only be
 * called if iommufd_device_attach() has already succeeded.
 */
int iommufd_device_replace(struct iommufd_device *idev, u32 *pt_id)
{
	return iommufd_device_change_pt(idev, pt_id,
					&iommufd_device_do_replace);
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_replace, IOMMUFD);

/**
 * iommufd_device_detach - Disconnect a device to an iommu_domain
 * @idev: device to detach
 *
 * Undo iommufd_device_attach(). This disconnects the idev from the previously
 * attached pt_id. The device returns back to a blocked DMA translation.
 */
void iommufd_device_detach(struct iommufd_device *idev)
{
	struct iommufd_hw_pagetable *hwpt;

	hwpt = iommufd_hw_pagetable_detach(idev);
	iommufd_hw_pagetable_put(idev->ictx, hwpt);
	refcount_dec(&idev->obj.users);
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_detach, IOMMUFD);

/*
 * On success, it will refcount_inc() at a valid new_ioas and refcount_dec() at
 * a valid cur_ioas (access->ioas). A caller passing in a valid new_ioas should
 * call iommufd_put_object() if it does an iommufd_get_object() for a new_ioas.
 */
static int iommufd_access_change_ioas(struct iommufd_access *access,
				      struct iommufd_ioas *new_ioas)
{
	u32 iopt_access_list_id = access->iopt_access_list_id;
	struct iommufd_ioas *cur_ioas = access->ioas;
	int rc;

	lockdep_assert_held(&access->ioas_lock);

	/* We are racing with a concurrent detach, bail */
	if (cur_ioas != access->ioas_unpin)
		return -EBUSY;

	if (cur_ioas == new_ioas)
		return 0;

	/*
	 * Set ioas to NULL to block any further iommufd_access_pin_pages().
	 * iommufd_access_unpin_pages() can continue using access->ioas_unpin.
	 */
	access->ioas = NULL;

	if (new_ioas) {
		rc = iopt_add_access(&new_ioas->iopt, access);
		if (rc) {
			access->ioas = cur_ioas;
			return rc;
		}
		refcount_inc(&new_ioas->obj.users);
	}

	if (cur_ioas) {
		if (access->ops->unmap) {
			mutex_unlock(&access->ioas_lock);
			access->ops->unmap(access->data, 0, ULONG_MAX);
			mutex_lock(&access->ioas_lock);
		}
		iopt_remove_access(&cur_ioas->iopt, access, iopt_access_list_id);
		refcount_dec(&cur_ioas->obj.users);
	}

	access->ioas = new_ioas;
	access->ioas_unpin = new_ioas;

	return 0;
}

static int iommufd_access_change_ioas_id(struct iommufd_access *access, u32 id)
{
	struct iommufd_ioas *ioas = iommufd_get_ioas(access->ictx, id);
	int rc;

	if (IS_ERR(ioas))
		return PTR_ERR(ioas);
	rc = iommufd_access_change_ioas(access, ioas);
	iommufd_put_object(&ioas->obj);
	return rc;
}

void iommufd_access_destroy_object(struct iommufd_object *obj)
{
	struct iommufd_access *access =
		container_of(obj, struct iommufd_access, obj);

	mutex_lock(&access->ioas_lock);
	if (access->ioas)
		WARN_ON(iommufd_access_change_ioas(access, NULL));
	mutex_unlock(&access->ioas_lock);
	iommufd_ctx_put(access->ictx);
}

/**
 * iommufd_access_create - Create an iommufd_access
 * @ictx: iommufd file descriptor
 * @ops: Driver's ops to associate with the access
 * @data: Opaque data to pass into ops functions
 * @id: Output ID number to return to userspace for this access
 *
 * An iommufd_access allows a driver to read/write to the IOAS without using
 * DMA. The underlying CPU memory can be accessed using the
 * iommufd_access_pin_pages() or iommufd_access_rw() functions.
 *
 * The provided ops are required to use iommufd_access_pin_pages().
 */
struct iommufd_access *
iommufd_access_create(struct iommufd_ctx *ictx,
		      const struct iommufd_access_ops *ops, void *data, u32 *id)
{
	struct iommufd_access *access;

	/*
	 * There is no uAPI for the access object, but to keep things symmetric
	 * use the object infrastructure anyhow.
	 */
	access = iommufd_object_alloc(ictx, access, IOMMUFD_OBJ_ACCESS);
	if (IS_ERR(access))
		return access;

	access->data = data;
	access->ops = ops;

	if (ops->needs_pin_pages)
		access->iova_alignment = PAGE_SIZE;
	else
		access->iova_alignment = 1;

	/* The calling driver is a user until iommufd_access_destroy() */
	refcount_inc(&access->obj.users);
	access->ictx = ictx;
	iommufd_ctx_get(ictx);
	iommufd_object_finalize(ictx, &access->obj);
	*id = access->obj.id;
	mutex_init(&access->ioas_lock);
	return access;
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_create, IOMMUFD);

/**
 * iommufd_access_destroy - Destroy an iommufd_access
 * @access: The access to destroy
 *
 * The caller must stop using the access before destroying it.
 */
void iommufd_access_destroy(struct iommufd_access *access)
{
	iommufd_object_destroy_user(access->ictx, &access->obj);
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_destroy, IOMMUFD);

void iommufd_access_detach(struct iommufd_access *access)
{
	mutex_lock(&access->ioas_lock);
	if (WARN_ON(!access->ioas)) {
		mutex_unlock(&access->ioas_lock);
		return;
	}
	WARN_ON(iommufd_access_change_ioas(access, NULL));
	mutex_unlock(&access->ioas_lock);
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_detach, IOMMUFD);

int iommufd_access_attach(struct iommufd_access *access, u32 ioas_id)
{
	int rc;

	mutex_lock(&access->ioas_lock);
	if (WARN_ON(access->ioas)) {
		mutex_unlock(&access->ioas_lock);
		return -EINVAL;
	}

	rc = iommufd_access_change_ioas_id(access, ioas_id);
	mutex_unlock(&access->ioas_lock);
	return rc;
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_attach, IOMMUFD);

int iommufd_access_replace(struct iommufd_access *access, u32 ioas_id)
{
	int rc;

	mutex_lock(&access->ioas_lock);
	if (!access->ioas) {
		mutex_unlock(&access->ioas_lock);
		return -ENOENT;
	}
	rc = iommufd_access_change_ioas_id(access, ioas_id);
	mutex_unlock(&access->ioas_lock);
	return rc;
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_replace, IOMMUFD);

/**
 * iommufd_access_notify_unmap - Notify users of an iopt to stop using it
 * @iopt: iopt to work on
 * @iova: Starting iova in the iopt
 * @length: Number of bytes
 *
 * After this function returns there should be no users attached to the pages
 * linked to this iopt that intersect with iova,length. Anyone that has attached
 * a user through iopt_access_pages() needs to detach it through
 * iommufd_access_unpin_pages() before this function returns.
 *
 * iommufd_access_destroy() will wait for any outstanding unmap callback to
 * complete. Once iommufd_access_destroy() no unmap ops are running or will
 * run in the future. Due to this a driver must not create locking that prevents
 * unmap to complete while iommufd_access_destroy() is running.
 */
void iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long iova,
				 unsigned long length)
{
	struct iommufd_ioas *ioas =
		container_of(iopt, struct iommufd_ioas, iopt);
	struct iommufd_access *access;
	unsigned long index;

	xa_lock(&ioas->iopt.access_list);
	xa_for_each(&ioas->iopt.access_list, index, access) {
		if (!iommufd_lock_obj(&access->obj))
			continue;
		xa_unlock(&ioas->iopt.access_list);

		access->ops->unmap(access->data, iova, length);

		iommufd_put_object(&access->obj);
		xa_lock(&ioas->iopt.access_list);
	}
	xa_unlock(&ioas->iopt.access_list);
}

/**
 * iommufd_access_unpin_pages() - Undo iommufd_access_pin_pages
 * @access: IOAS access to act on
 * @iova: Starting IOVA
 * @length: Number of bytes to access
 *
 * Return the struct page's. The caller must stop accessing them before calling
 * this. The iova/length must exactly match the one provided to access_pages.
 */
void iommufd_access_unpin_pages(struct iommufd_access *access,
				unsigned long iova, unsigned long length)
{
	struct iopt_area_contig_iter iter;
	struct io_pagetable *iopt;
	unsigned long last_iova;
	struct iopt_area *area;

	if (WARN_ON(!length) ||
	    WARN_ON(check_add_overflow(iova, length - 1, &last_iova)))
		return;

	mutex_lock(&access->ioas_lock);
	/*
	 * The driver must be doing something wrong if it calls this before an
	 * iommufd_access_attach() or after an iommufd_access_detach().
	 */
	if (WARN_ON(!access->ioas_unpin)) {
		mutex_unlock(&access->ioas_lock);
		return;
	}
	iopt = &access->ioas_unpin->iopt;

	down_read(&iopt->iova_rwsem);
	iopt_for_each_contig_area(&iter, area, iopt, iova, last_iova)
		iopt_area_remove_access(
			area, iopt_area_iova_to_index(area, iter.cur_iova),
			iopt_area_iova_to_index(
				area,
				min(last_iova, iopt_area_last_iova(area))));
	WARN_ON(!iopt_area_contig_done(&iter));
	up_read(&iopt->iova_rwsem);
	mutex_unlock(&access->ioas_lock);
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_unpin_pages, IOMMUFD);

static bool iopt_area_contig_is_aligned(struct iopt_area_contig_iter *iter)
{
	if (iopt_area_start_byte(iter->area, iter->cur_iova) % PAGE_SIZE)
		return false;

	if (!iopt_area_contig_done(iter) &&
	    (iopt_area_start_byte(iter->area, iopt_area_last_iova(iter->area)) %
	     PAGE_SIZE) != (PAGE_SIZE - 1))
		return false;
	return true;
}

static bool check_area_prot(struct iopt_area *area, unsigned int flags)
{
	if (flags & IOMMUFD_ACCESS_RW_WRITE)
		return area->iommu_prot & IOMMU_WRITE;
	return area->iommu_prot & IOMMU_READ;
}

/**
 * iommufd_access_pin_pages() - Return a list of pages under the iova
 * @access: IOAS access to act on
 * @iova: Starting IOVA
 * @length: Number of bytes to access
 * @out_pages: Output page list
 * @flags: IOPMMUFD_ACCESS_RW_* flags
 *
 * Reads @length bytes starting at iova and returns the struct page * pointers.
 * These can be kmap'd by the caller for CPU access.
 *
 * The caller must perform iommufd_access_unpin_pages() when done to balance
 * this.
 *
 * This API always requires a page aligned iova. This happens naturally if the
 * ioas alignment is >= PAGE_SIZE and the iova is PAGE_SIZE aligned. However
 * smaller alignments have corner cases where this API can fail on otherwise
 * aligned iova.
 */
int iommufd_access_pin_pages(struct iommufd_access *access, unsigned long iova,
			     unsigned long length, struct page **out_pages,
			     unsigned int flags)
{
	struct iopt_area_contig_iter iter;
	struct io_pagetable *iopt;
	unsigned long last_iova;
	struct iopt_area *area;
	int rc;

	/* Driver's ops don't support pin_pages */
	if (IS_ENABLED(CONFIG_IOMMUFD_TEST) &&
	    WARN_ON(access->iova_alignment != PAGE_SIZE || !access->ops->unmap))
		return -EINVAL;

	if (!length)
		return -EINVAL;
	if (check_add_overflow(iova, length - 1, &last_iova))
		return -EOVERFLOW;

	mutex_lock(&access->ioas_lock);
	if (!access->ioas) {
		mutex_unlock(&access->ioas_lock);
		return -ENOENT;
	}
	iopt = &access->ioas->iopt;

	down_read(&iopt->iova_rwsem);
	iopt_for_each_contig_area(&iter, area, iopt, iova, last_iova) {
		unsigned long last = min(last_iova, iopt_area_last_iova(area));
		unsigned long last_index = iopt_area_iova_to_index(area, last);
		unsigned long index =
			iopt_area_iova_to_index(area, iter.cur_iova);

		if (area->prevent_access ||
		    !iopt_area_contig_is_aligned(&iter)) {
			rc = -EINVAL;
			goto err_remove;
		}

		if (!check_area_prot(area, flags)) {
			rc = -EPERM;
			goto err_remove;
		}

		rc = iopt_area_add_access(area, index, last_index, out_pages,
					  flags);
		if (rc)
			goto err_remove;
		out_pages += last_index - index + 1;
	}
	if (!iopt_area_contig_done(&iter)) {
		rc = -ENOENT;
		goto err_remove;
	}

	up_read(&iopt->iova_rwsem);
	mutex_unlock(&access->ioas_lock);
	return 0;

err_remove:
	if (iova < iter.cur_iova) {
		last_iova = iter.cur_iova - 1;
		iopt_for_each_contig_area(&iter, area, iopt, iova, last_iova)
			iopt_area_remove_access(
				area,
				iopt_area_iova_to_index(area, iter.cur_iova),
				iopt_area_iova_to_index(
					area, min(last_iova,
						  iopt_area_last_iova(area))));
	}
	up_read(&iopt->iova_rwsem);
	mutex_unlock(&access->ioas_lock);
	return rc;
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_pin_pages, IOMMUFD);

/**
 * iommufd_access_rw - Read or write data under the iova
 * @access: IOAS access to act on
 * @iova: Starting IOVA
 * @data: Kernel buffer to copy to/from
 * @length: Number of bytes to access
 * @flags: IOMMUFD_ACCESS_RW_* flags
 *
 * Copy kernel to/from data into the range given by IOVA/length. If flags
 * indicates IOMMUFD_ACCESS_RW_KTHREAD then a large copy can be optimized
 * by changing it into copy_to/from_user().
 */
int iommufd_access_rw(struct iommufd_access *access, unsigned long iova,
		      void *data, size_t length, unsigned int flags)
{
	struct iopt_area_contig_iter iter;
	struct io_pagetable *iopt;
	struct iopt_area *area;
	unsigned long last_iova;
	int rc;

	if (!length)
		return -EINVAL;
	if (check_add_overflow(iova, length - 1, &last_iova))
		return -EOVERFLOW;

	mutex_lock(&access->ioas_lock);
	if (!access->ioas) {
		mutex_unlock(&access->ioas_lock);
		return -ENOENT;
	}
	iopt = &access->ioas->iopt;

	down_read(&iopt->iova_rwsem);
	iopt_for_each_contig_area(&iter, area, iopt, iova, last_iova) {
		unsigned long last = min(last_iova, iopt_area_last_iova(area));
		unsigned long bytes = (last - iter.cur_iova) + 1;

		if (area->prevent_access) {
			rc = -EINVAL;
			goto err_out;
		}

		if (!check_area_prot(area, flags)) {
			rc = -EPERM;
			goto err_out;
		}

		rc = iopt_pages_rw_access(
			area->pages, iopt_area_start_byte(area, iter.cur_iova),
			data, bytes, flags);
		if (rc)
			goto err_out;
		data += bytes;
	}
	if (!iopt_area_contig_done(&iter))
		rc = -ENOENT;
err_out:
	up_read(&iopt->iova_rwsem);
	mutex_unlock(&access->ioas_lock);
	return rc;
}
EXPORT_SYMBOL_NS_GPL(iommufd_access_rw, IOMMUFD);

int iommufd_get_hw_info(struct iommufd_ucmd *ucmd)
{
	struct iommu_hw_info *cmd = ucmd->cmd;
	void __user *user_ptr = u64_to_user_ptr(cmd->data_uptr);
	const struct iommu_ops *ops;
	struct iommufd_device *idev;
	unsigned int data_len;
	unsigned int copy_len;
	void *data;
	int rc;

	if (cmd->flags || cmd->__reserved)
		return -EOPNOTSUPP;

	idev = iommufd_get_device(ucmd, cmd->dev_id);
	if (IS_ERR(idev))
		return PTR_ERR(idev);

	ops = dev_iommu_ops(idev->dev);
	if (ops->hw_info) {
		data = ops->hw_info(idev->dev, &data_len, &cmd->out_data_type);
		if (IS_ERR(data)) {
			rc = PTR_ERR(data);
			goto out_put;
		}

		/*
		 * drivers that have hw_info callback should have a unique
		 * iommu_hw_info_type.
		 */
		if (WARN_ON_ONCE(cmd->out_data_type ==
				 IOMMU_HW_INFO_TYPE_NONE)) {
			rc = -ENODEV;
			goto out_free;
		}
	} else {
		cmd->out_data_type = IOMMU_HW_INFO_TYPE_NONE;
		data_len = 0;
		data = NULL;
	}

	copy_len = min(cmd->data_len, data_len);
	if (copy_to_user(user_ptr, data, copy_len)) {
		rc = -EFAULT;
		goto out_free;
	}

	/*
	 * Zero the trailing bytes if the user buffer is bigger than the
	 * data size kernel actually has.
	 */
	if (copy_len < cmd->data_len) {
		if (clear_user(user_ptr + copy_len, cmd->data_len - copy_len)) {
			rc = -EFAULT;
			goto out_free;
		}
	}

	/*
	 * We return the length the kernel supports so userspace may know what
	 * the kernel capability is. It could be larger than the input buffer.
	 */
	cmd->data_len = data_len;

	cmd->out_capabilities = 0;
	if (device_iommu_capable(idev->dev, IOMMU_CAP_DIRTY_TRACKING))
		cmd->out_capabilities |= IOMMU_HW_CAP_DIRTY_TRACKING;

	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
out_free:
	kfree(data);
out_put:
	iommufd_put_object(&idev->obj);
	return rc;
}