iommufd: Add kAPI toward external drivers for physical devices

Add the four functions external drivers need to connect physical DMA to
the IOMMUFD:

iommufd_device_bind() / iommufd_device_unbind()
  Register the device with iommufd and establish security isolation.

iommufd_device_attach() / iommufd_device_detach()
  Connect a bound device to a page table

Binding a device creates a device object ID in the uAPI, however the
generic API does not yet provide any IOCTLs to manipulate them.

Link: https://lore.kernel.org/r/13-v6-a196d26f289e+11787-iommufd_jgg@nvidia.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Yi Liu <yi.l.liu@intel.com>
Tested-by: Lixiao Yang <lixiao.yang@intel.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 iommufd-y := \
+	device.o \
 	hw_pagetable.o \
 	io_pagetable.o \
 	ioas.o \

drivers/iommu/iommufd/device.c

@@ -0,0 +1,419 @@
+// 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 <linux/irqdomain.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.");
+
+/*
+ * A iommufd_device object represents the binding relationship between a
+ * consuming driver and the iommufd. These objects are created/destroyed by
+ * external drivers, not by userspace.
+ */
+struct iommufd_device {
+	struct iommufd_object obj;
+	struct iommufd_ctx *ictx;
+	struct iommufd_hw_pagetable *hwpt;
+	/* Head at iommufd_hw_pagetable::devices */
+	struct list_head devices_item;
+	/* always the physical device */
+	struct device *dev;
+	struct iommu_group *group;
+	bool enforce_cache_coherency;
+};
+
+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);
+	iommu_group_put(idev->group);
+	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 iommu_group *group;
+	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);
+
+	group = iommu_group_get(dev);
+	if (!group)
+		return ERR_PTR(-ENODEV);
+
+	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;
+	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);
+	/* group refcount moves into iommufd_device */
+	idev->group = group;
+
+	/*
+	 * 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:
+	iommu_group_put(group);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_device_bind, 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)
+{
+	bool was_destroyed;
+
+	was_destroyed = iommufd_object_destroy_user(idev->ictx, &idev->obj);
+	WARN_ON(!was_destroyed);
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_device_unbind, IOMMUFD);
+
+static int iommufd_device_setup_msi(struct iommufd_device *idev,
+				    struct iommufd_hw_pagetable *hwpt,
+				    phys_addr_t sw_msi_start)
+{
+	int rc;
+
+	/*
+	 * IOMMU_CAP_INTR_REMAP means that the platform is isolating MSI, and it
+	 * creates the MSI window by default in the iommu domain. Nothing
+	 * further to do.
+	 */
+	if (device_iommu_capable(idev->dev, IOMMU_CAP_INTR_REMAP))
+		return 0;
+
+	/*
+	 * On ARM systems that set the global IRQ_DOMAIN_FLAG_MSI_REMAP every
+	 * allocated iommu_domain will block interrupts by default and this
+	 * special flow is needed to turn them back on. iommu_dma_prepare_msi()
+	 * will install pages into our domain after request_irq() to make this
+	 * work.
+	 *
+	 * 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 (irq_domain_check_msi_remap()) {
+		if (WARN_ON(!sw_msi_start))
+			return -EPERM;
+		/*
+		 * iommu_get_msi_cookie() can only be called once per domain,
+		 * it returns -EBUSY on later calls.
+		 */
+		if (hwpt->msi_cookie)
+			return 0;
+		rc = iommu_get_msi_cookie(hwpt->domain, sw_msi_start);
+		if (rc)
+			return rc;
+		hwpt->msi_cookie = true;
+		return 0;
+	}
+
+	/*
+	 * Otherwise the platform has a MSI window that is not isolated. For
+	 * historical compat with VFIO allow a module parameter to ignore the
+	 * insecurity.
+	 */
+	if (!allow_unsafe_interrupts)
+		return -EPERM;
+
+	dev_warn(
+		idev->dev,
+		"MSI interrupt window cannot be isolated by the IOMMU, this platform is insecure. Use the \"allow_unsafe_interrupts\" module parameter to override\n");
+	return 0;
+}
+
+static bool iommufd_hw_pagetable_has_group(struct iommufd_hw_pagetable *hwpt,
+					   struct iommu_group *group)
+{
+	struct iommufd_device *cur_dev;
+
+	list_for_each_entry(cur_dev, &hwpt->devices, devices_item)
+		if (cur_dev->group == group)
+			return true;
+	return false;
+}
+
+static int iommufd_device_do_attach(struct iommufd_device *idev,
+				    struct iommufd_hw_pagetable *hwpt)
+{
+	phys_addr_t sw_msi_start = 0;
+	int rc;
+
+	mutex_lock(&hwpt->devices_lock);
+
+	/*
+	 * Try to upgrade the domain we have, it is an iommu driver bug to
+	 * report IOMMU_CAP_ENFORCE_CACHE_COHERENCY but fail
+	 * enforce_cache_coherency when there are no devices attached to the
+	 * domain.
+	 */
+	if (idev->enforce_cache_coherency && !hwpt->enforce_cache_coherency) {
+		if (hwpt->domain->ops->enforce_cache_coherency)
+			hwpt->enforce_cache_coherency =
+				hwpt->domain->ops->enforce_cache_coherency(
+					hwpt->domain);
+		if (!hwpt->enforce_cache_coherency) {
+			WARN_ON(list_empty(&hwpt->devices));
+			rc = -EINVAL;
+			goto out_unlock;
+		}
+	}
+
+	rc = iopt_table_enforce_group_resv_regions(&hwpt->ioas->iopt, idev->dev,
+						   idev->group, &sw_msi_start);
+	if (rc)
+		goto out_unlock;
+
+	rc = iommufd_device_setup_msi(idev, hwpt, sw_msi_start);
+	if (rc)
+		goto out_iova;
+
+	/*
+	 * FIXME: Hack around missing a device-centric iommu api, only attach to
+	 * the group once for the first device that is in the group.
+	 */
+	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
+		rc = iommu_attach_group(hwpt->domain, idev->group);
+		if (rc)
+			goto out_iova;
+
+		if (list_empty(&hwpt->devices)) {
+			rc = iopt_table_add_domain(&hwpt->ioas->iopt,
+						   hwpt->domain);
+			if (rc)
+				goto out_detach;
+		}
+	}
+
+	idev->hwpt = hwpt;
+	refcount_inc(&hwpt->obj.users);
+	list_add(&idev->devices_item, &hwpt->devices);
+	mutex_unlock(&hwpt->devices_lock);
+	return 0;
+
+out_detach:
+	iommu_detach_group(hwpt->domain, idev->group);
+out_iova:
+	iopt_remove_reserved_iova(&hwpt->ioas->iopt, idev->dev);
+out_unlock:
+	mutex_unlock(&hwpt->devices_lock);
+	return rc;
+}
+
+/*
+ * 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 int iommufd_device_auto_get_domain(struct iommufd_device *idev,
+					  struct iommufd_ioas *ioas)
+{
+	struct iommufd_hw_pagetable *hwpt;
+	int rc;
+
+	/*
+	 * 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, &ioas->hwpt_list, hwpt_item) {
+		if (!hwpt->auto_domain)
+			continue;
+
+		rc = iommufd_device_do_attach(idev, hwpt);
+
+		/*
+		 * -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 (rc == -EINVAL)
+			continue;
+		goto out_unlock;
+	}
+
+	hwpt = iommufd_hw_pagetable_alloc(idev->ictx, ioas, idev->dev);
+	if (IS_ERR(hwpt)) {
+		rc = PTR_ERR(hwpt);
+		goto out_unlock;
+	}
+	hwpt->auto_domain = true;
+
+	rc = iommufd_device_do_attach(idev, hwpt);
+	if (rc)
+		goto out_abort;
+	list_add_tail(&hwpt->hwpt_item, &ioas->hwpt_list);
+
+	mutex_unlock(&ioas->mutex);
+	iommufd_object_finalize(idev->ictx, &hwpt->obj);
+	return 0;
+
+out_abort:
+	iommufd_object_abort_and_destroy(idev->ictx, &hwpt->obj);
+out_unlock:
+	mutex_unlock(&ioas->mutex);
+	return rc;
+}
+
+/**
+ * iommufd_device_attach - Connect a device from an iommu_domain
+ * @idev: device to attach
+ * @pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HW_PAGETABLE
+ *         Output the IOMMUFD_OBJ_HW_PAGETABLE 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)
+{
+	struct iommufd_object *pt_obj;
+	int rc;
+
+	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_HW_PAGETABLE: {
+		struct iommufd_hw_pagetable *hwpt =
+			container_of(pt_obj, struct iommufd_hw_pagetable, obj);
+
+		rc = iommufd_device_do_attach(idev, hwpt);
+		if (rc)
+			goto out_put_pt_obj;
+
+		mutex_lock(&hwpt->ioas->mutex);
+		list_add_tail(&hwpt->hwpt_item, &hwpt->ioas->hwpt_list);
+		mutex_unlock(&hwpt->ioas->mutex);
+		break;
+	}
+	case IOMMUFD_OBJ_IOAS: {
+		struct iommufd_ioas *ioas =
+			container_of(pt_obj, struct iommufd_ioas, obj);
+
+		rc = iommufd_device_auto_get_domain(idev, ioas);
+		if (rc)
+			goto out_put_pt_obj;
+		break;
+	}
+	default:
+		rc = -EINVAL;
+		goto out_put_pt_obj;
+	}
+
+	refcount_inc(&idev->obj.users);
+	*pt_id = idev->hwpt->obj.id;
+	rc = 0;
+
+out_put_pt_obj:
+	iommufd_put_object(pt_obj);
+	return rc;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_device_attach, 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 = idev->hwpt;
+
+	mutex_lock(&hwpt->ioas->mutex);
+	mutex_lock(&hwpt->devices_lock);
+	list_del(&idev->devices_item);
+	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
+		if (list_empty(&hwpt->devices)) {
+			iopt_table_remove_domain(&hwpt->ioas->iopt,
+						 hwpt->domain);
+			list_del(&hwpt->hwpt_item);
+		}
+		iommu_detach_group(hwpt->domain, idev->group);
+	}
+	iopt_remove_reserved_iova(&hwpt->ioas->iopt, idev->dev);
+	mutex_unlock(&hwpt->devices_lock);
+	mutex_unlock(&hwpt->ioas->mutex);
+
+	if (hwpt->auto_domain)
+		iommufd_object_destroy_user(idev->ictx, &hwpt->obj);
+	else
+		refcount_dec(&hwpt->obj.users);
+
+	idev->hwpt = NULL;
+
+	refcount_dec(&idev->obj.users);
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_device_detach, IOMMUFD);

drivers/iommu/iommufd/iommufd_private.h

@@ -103,6 +103,7 @@ static inline int iommufd_ucmd_respond(struct iommufd_ucmd *ucmd,
 enum iommufd_object_type {
 	IOMMUFD_OBJ_NONE,
 	IOMMUFD_OBJ_ANY = IOMMUFD_OBJ_NONE,
+	IOMMUFD_OBJ_DEVICE,
 	IOMMUFD_OBJ_HW_PAGETABLE,
 	IOMMUFD_OBJ_IOAS,
 };
@@ -229,6 +230,8 @@ struct iommufd_hw_pagetable {
 	struct iommufd_ioas *ioas;
 	struct iommu_domain *domain;
 	bool auto_domain : 1;
+	bool enforce_cache_coherency : 1;
+	bool msi_cookie : 1;
 	/* Head at iommufd_ioas::hwpt_list */
 	struct list_head hwpt_item;
 	struct mutex devices_lock;
@@ -240,6 +243,8 @@ iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
 			   struct device *dev);
 void iommufd_hw_pagetable_destroy(struct iommufd_object *obj);
 
+void iommufd_device_destroy(struct iommufd_object *obj);
+
 struct iommufd_access {
 	unsigned long iova_alignment;
 	u32 iopt_access_list_id;

drivers/iommu/iommufd/main.c

@@ -357,6 +357,9 @@ void iommufd_ctx_put(struct iommufd_ctx *ictx)
 EXPORT_SYMBOL_NS_GPL(iommufd_ctx_put, IOMMUFD);
 
 static const struct iommufd_object_ops iommufd_object_ops[] = {
+	[IOMMUFD_OBJ_DEVICE] = {
+		.destroy = iommufd_device_destroy,
+	},
 	[IOMMUFD_OBJ_IOAS] = {
 		.destroy = iommufd_ioas_destroy,
 	},

include/linux/iommufd.h

@@ -9,10 +9,19 @@
 #include <linux/types.h>
 #include <linux/errno.h>
 #include <linux/err.h>
+#include <linux/device.h>
 
+struct iommufd_device;
 struct iommufd_ctx;
 struct file;
 
+struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
+					   struct device *dev, u32 *id);
+void iommufd_device_unbind(struct iommufd_device *idev);
+
+int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id);
+void iommufd_device_detach(struct iommufd_device *idev);
+
 enum {
 	IOMMUFD_ACCESS_RW_READ = 0,
 	IOMMUFD_ACCESS_RW_WRITE = 1 << 0,