drm: Add drm_object lease infrastructure [v5]

This provides new data structures to hold "lease" information about
drm mode setting objects, and provides for creating new drm_masters
which have access to a subset of the available drm resources.

An 'owner' is a drm_master which is not leasing the objects from
another drm_master, and hence 'owns' them.

A 'lessee' is a drm_master which is leasing objects from some other
drm_master. Each lessee holds the set of objects which it is leasing
from the lessor.

A 'lessor' is a drm_master which is leasing objects to another
drm_master. This is the same as the owner in the current code.

The set of objects any drm_master 'controls' is limited to the set of
objects it leases (for lessees) or all objects (for owners).

Objects not controlled by a drm_master cannot be modified through the
various state manipulating ioctls, and any state reported back to user
space will be edited to make them appear idle and/or unusable. For
instance, connectors always report 'disconnected', while encoders
report no possible crtcs or clones.

The full list of lessees leasing objects from an owner (either
directly, or indirectly through another lessee), can be searched from
an idr in the drm_master of the owner.

Changes for v2 as suggested by Daniel Vetter <daniel.vetter@ffwll.ch>:

* Sub-leasing has been disabled.

* BUG_ON for lock checking replaced with lockdep_assert_held

* 'change' ioctl has been removed.

* Leased objects can always be controlled by the lessor; the
  'mask_lease' flag has been removed

* Checking for leased status has been simplified, replacing
  the drm_lease_check function with drm_lease_held.

Changes in v3, some suggested by Dave Airlie <airlied@gmail.com>

* Add revocation. This allows leases to be effectively revoked by
  removing all of the objects they have access to. The lease itself
  hangs around as it's hanging off a file.

* Free the leases IDR when the master is destroyed

* _drm_lease_held should look at lessees, not lessor

* Allow non-master files to check for lease status

Changes in v4, suggested by Dave Airlie <airlied@gmail.com>

* Formatting and whitespace changes

Changes in v5 (airlied)

* check DRIVER_MODESET before lease destroy call
* check DRIVER_MODESET for lease revoke (Chris)
* Use idr_mutex uniformly for all lease elements of struct drm_master. (Keith)

Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/Makefile

@@ -17,7 +17,7 @@ drm-y       :=	drm_auth.o drm_bufs.o drm_cache.o \
 		drm_encoder.o drm_mode_object.o drm_property.o \
 		drm_plane.o drm_color_mgmt.o drm_print.o \
 		drm_dumb_buffers.o drm_mode_config.o drm_vblank.o \
-		drm_syncobj.o
+		drm_syncobj.o drm_lease.o
 
 drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_DRM_VM) += drm_vm.o

drivers/gpu/drm/drm_auth.c

@@ -31,6 +31,7 @@
 #include <drm/drmP.h>
 #include "drm_internal.h"
 #include "drm_legacy.h"
+#include <drm/drm_lease.h>
 
 /**
  * DOC: master and authentication
@@ -93,7 +94,7 @@ int drm_authmagic(struct drm_device *dev, void *data,
 	return file ? 0 : -EINVAL;
 }
 
-static struct drm_master *drm_master_create(struct drm_device *dev)
+struct drm_master *drm_master_create(struct drm_device *dev)
 {
 	struct drm_master *master;
 
@@ -107,6 +108,14 @@ static struct drm_master *drm_master_create(struct drm_device *dev)
 	idr_init(&master->magic_map);
 	master->dev = dev;
 
+	/* initialize the tree of output resource lessees */
+	master->lessor = NULL;
+	master->lessee_id = 0;
+	INIT_LIST_HEAD(&master->lessees);
+	INIT_LIST_HEAD(&master->lessee_list);
+	idr_init(&master->leases);
+	idr_init(&master->lessee_idr);
+
 	return master;
 }
 
@@ -189,6 +198,12 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
 		goto out_unlock;
 	}
 
+	if (file_priv->master->lessor != NULL) {
+		DRM_DEBUG_LEASE("Attempt to set lessee %d as master\n", file_priv->master->lessee_id);
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	ret = drm_set_master(dev, file_priv, false);
 out_unlock:
 	mutex_unlock(&dev->master_mutex);
@@ -270,6 +285,13 @@ void drm_master_release(struct drm_file *file_priv)
 	if (dev->master == file_priv->master)
 		drm_drop_master(dev, file_priv);
 out:
+	if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) {
+		/* Revoke any leases held by this or lessees, but only if
+		 * this is the "real" master
+		 */
+		drm_lease_revoke(master);
+	}
+
 	/* drop the master reference held by the file priv */
 	if (file_priv->master)
 		drm_master_put(&file_priv->master);
@@ -310,12 +332,18 @@ static void drm_master_destroy(struct kref *kref)
 	struct drm_master *master = container_of(kref, struct drm_master, refcount);
 	struct drm_device *dev = master->dev;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		drm_lease_destroy(master);
+
 	if (dev->driver->master_destroy)
 		dev->driver->master_destroy(dev, master);
 
 	drm_legacy_master_rmmaps(dev, master);
 
 	idr_destroy(&master->magic_map);
+	idr_destroy(&master->leases);
+	idr_destroy(&master->lessee_idr);
+
 	kfree(master->unique);
 	kfree(master);
 }

drivers/gpu/drm/drm_lease.c

@@ -0,0 +1,355 @@
+/*
+ * Copyright © 2017 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <drm/drmP.h>
+#include "drm_internal.h"
+#include "drm_legacy.h"
+#include "drm_crtc_internal.h"
+#include <drm/drm_lease.h>
+#include <drm/drm_auth.h>
+#include <drm/drm_crtc_helper.h>
+
+#define drm_for_each_lessee(lessee, lessor) \
+	list_for_each_entry((lessee), &(lessor)->lessees, lessee_list)
+
+/**
+ * drm_lease_owner - return ancestor owner drm_master
+ * @master: drm_master somewhere within tree of lessees and lessors
+ *
+ * RETURN:
+ *
+ * drm_master at the top of the tree (i.e, with lessor NULL
+ */
+struct drm_master *drm_lease_owner(struct drm_master *master)
+{
+	while (master->lessor != NULL)
+		master = master->lessor;
+	return master;
+}
+EXPORT_SYMBOL(drm_lease_owner);
+
+/**
+ * _drm_find_lessee - find lessee by id (idr_mutex held)
+ * @master: drm_master of lessor
+ * @id: lessee_id
+ *
+ * RETURN:
+ *
+ * drm_master of the lessee if valid, NULL otherwise
+ */
+
+static struct drm_master*
+_drm_find_lessee(struct drm_master *master, int lessee_id)
+{
+	lockdep_assert_held(&master->dev->mode_config.idr_mutex);
+	return idr_find(&drm_lease_owner(master)->lessee_idr, lessee_id);
+}
+
+/**
+ * _drm_lease_held_master - check to see if an object is leased (or owned) by master (idr_mutex held)
+ * @master: the master to check the lease status of
+ * @id: the id to check
+ *
+ * Checks if the specified master holds a lease on the object. Return
+ * value:
+ *
+ *	true		'master' holds a lease on (or owns) the object
+ *	false		'master' does not hold a lease.
+ */
+static int _drm_lease_held_master(struct drm_master *master, int id)
+{
+	lockdep_assert_held(&master->dev->mode_config.idr_mutex);
+	if (master->lessor)
+		return idr_find(&master->leases, id) != NULL;
+	return true;
+}
+
+/**
+ * _drm_has_leased - check to see if an object has been leased (idr_mutex held)
+ * @master: the master to check the lease status of
+ * @id: the id to check
+ *
+ * Checks if any lessee of 'master' holds a lease on 'id'. Return
+ * value:
+ *
+ *	true		Some lessee holds a lease on the object.
+ *	false		No lessee has a lease on the object.
+ */
+static bool _drm_has_leased(struct drm_master *master, int id)
+{
+	struct drm_master *lessee;
+
+	lockdep_assert_held(&master->dev->mode_config.idr_mutex);
+	drm_for_each_lessee(lessee, master)
+		if (_drm_lease_held_master(lessee, id))
+			return true;
+	return false;
+}
+
+/**
+ * _drm_lease_held - check drm_mode_object lease status (idr_mutex held)
+ * @master: the drm_master
+ * @id: the object id
+ *
+ * Checks if the specified master holds a lease on the object. Return
+ * value:
+ *
+ *	true		'master' holds a lease on (or owns) the object
+ *	false		'master' does not hold a lease.
+ */
+bool _drm_lease_held(struct drm_file *file_priv, int id)
+{
+	if (file_priv == NULL || file_priv->master == NULL)
+		return true;
+
+	return _drm_lease_held_master(file_priv->master, id);
+}
+EXPORT_SYMBOL(_drm_lease_held);
+
+/**
+ * drm_lease_held - check drm_mode_object lease status (idr_mutex not held)
+ * @master: the drm_master
+ * @id: the object id
+ *
+ * Checks if the specified master holds a lease on the object. Return
+ * value:
+ *
+ *	true		'master' holds a lease on (or owns) the object
+ *	false		'master' does not hold a lease.
+ */
+bool drm_lease_held(struct drm_file *file_priv, int id)
+{
+	struct drm_master *master;
+	bool ret;
+
+	if (file_priv == NULL || file_priv->master == NULL)
+		return true;
+
+	master = file_priv->master;
+	mutex_lock(&master->dev->mode_config.idr_mutex);
+	ret = _drm_lease_held_master(master, id);
+	mutex_unlock(&master->dev->mode_config.idr_mutex);
+	return ret;
+}
+EXPORT_SYMBOL(drm_lease_held);
+
+/**
+ * drm_lease_filter_crtcs - restricted crtc set to leased values (idr_mutex not held)
+ * @file_priv: requestor file
+ * @crtcs: bitmask of crtcs to check
+ *
+ * Reconstructs a crtc mask based on the crtcs which are visible
+ * through the specified file.
+ */
+uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in)
+{
+	struct drm_master *master;
+	struct drm_device *dev;
+	struct drm_crtc *crtc;
+	int count_in, count_out;
+	uint32_t crtcs_out = 0;
+
+	if (file_priv == NULL || file_priv->master == NULL)
+		return crtcs_in;
+
+	master = file_priv->master;
+	dev = master->dev;
+
+	count_in = count_out = 0;
+	mutex_lock(&master->dev->mode_config.idr_mutex);
+	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
+		if (_drm_lease_held_master(master, crtc->base.id)) {
+			uint32_t mask_in = 1ul << count_in;
+			if ((crtcs_in & mask_in) != 0) {
+				uint32_t mask_out = 1ul << count_out;
+				crtcs_out |= mask_out;
+			}
+			count_out++;
+		}
+		count_in++;
+	}
+	mutex_unlock(&master->dev->mode_config.idr_mutex);
+	return crtcs_out;
+}
+EXPORT_SYMBOL(drm_lease_filter_crtcs);
+
+/*
+ * drm_lease_create - create a new drm_master with leased objects (idr_mutex not held)
+ * @lessor: lease holder (or owner) of objects
+ * @leases: objects to lease to the new drm_master
+ *
+ * Uses drm_master_create to allocate a new drm_master, then checks to
+ * make sure all of the desired objects can be leased, atomically
+ * leasing them to the new drmmaster.
+ *
+ * 	ERR_PTR(-EACCESS)	some other master holds the title to any object
+ * 	ERR_PTR(-ENOENT)	some object is not a valid DRM object for this device
+ * 	ERR_PTR(-EBUSY)		some other lessee holds title to this object
+ *	ERR_PTR(-EEXIST)	same object specified more than once in the provided list
+ *	ERR_PTR(-ENOMEM)	allocation failed
+ */
+static struct drm_master *drm_lease_create(struct drm_master *lessor, struct idr *leases)
+{
+	struct drm_device *dev = lessor->dev;
+	int error;
+	struct drm_master *lessee;
+	int object;
+	int id;
+	void *entry;
+
+	DRM_DEBUG_LEASE("lessor %d\n", lessor->lessee_id);
+
+	lessee = drm_master_create(lessor->dev);
+	if (!lessee) {
+		DRM_DEBUG_LEASE("drm_master_create failed\n");
+		return ERR_PTR(-ENOMEM);
+	}
+
+	mutex_lock(&dev->mode_config.idr_mutex);
+
+	/* Insert the new lessee into the tree */
+	id = idr_alloc(&(drm_lease_owner(lessor)->lessee_idr), lessee, 1, 0, GFP_KERNEL);
+	if (id < 0) {
+		error = id;
+		goto out_lessee;
+	}
+
+	lessee->lessee_id = id;
+	lessee->lessor = drm_master_get(lessor);
+	list_add_tail(&lessee->lessee_list, &lessor->lessees);
+
+	idr_for_each_entry(leases, entry, object) {
+		error = 0;
+		if (!idr_find(&dev->mode_config.crtc_idr, object))
+			error = -ENOENT;
+		else if (!_drm_lease_held_master(lessor, object))
+			error = -EACCES;
+		else if (_drm_has_leased(lessor, object))
+			error = -EBUSY;
+
+		if (error != 0) {
+			DRM_DEBUG_LEASE("object %d failed %d\n", object, error);
+			goto out_lessee;
+		}
+	}
+
+	/* Move the leases over */
+	lessee->leases = *leases;
+	DRM_DEBUG_LEASE("new lessee %d %p, lessor %d %p\n", lessee->lessee_id, lessee, lessor->lessee_id, lessor);
+
+	mutex_unlock(&dev->mode_config.idr_mutex);
+	return lessee;
+
+out_lessee:
+	drm_master_put(&lessee);
+
+	mutex_unlock(&dev->mode_config.idr_mutex);
+
+	return ERR_PTR(error);
+}
+
+/**
+ * drm_lease_destroy - a master is going away (idr_mutex not held)
+ * @master: the drm_master being destroyed
+ *
+ * All lessees will have been destroyed as they
+ * hold a reference on their lessor. Notify any
+ * lessor for this master so that it can check
+ * the list of lessees.
+ */
+void drm_lease_destroy(struct drm_master *master)
+{
+	struct drm_device *dev = master->dev;
+
+	mutex_lock(&dev->mode_config.idr_mutex);
+
+	DRM_DEBUG_LEASE("drm_lease_destroy %d\n", master->lessee_id);
+
+	/* This master is referenced by all lessees, hence it cannot be destroyed
+	 * until all of them have been
+	 */
+	WARN_ON(!list_empty(&master->lessees));
+
+	/* Remove this master from the lessee idr in the owner */
+	if (master->lessee_id != 0) {
+		DRM_DEBUG_LEASE("remove master %d from device list of lessees\n", master->lessee_id);
+		idr_remove(&(drm_lease_owner(master)->lessee_idr), master->lessee_id);
+	}
+
+	/* Remove this master from any lessee list it may be on */
+	list_del(&master->lessee_list);
+
+	mutex_unlock(&dev->mode_config.idr_mutex);
+
+	if (master->lessor) {
+		/* Tell the master to check the lessee list */
+		drm_sysfs_hotplug_event(dev);
+		drm_master_put(&master->lessor);
+	}
+
+	DRM_DEBUG_LEASE("drm_lease_destroy done %d\n", master->lessee_id);
+}
+
+/**
+ * _drm_lease_revoke - revoke access to all leased objects (idr_mutex held)
+ * @master: the master losing its lease
+ */
+static void _drm_lease_revoke(struct drm_master *top)
+{
+	int object;
+	void *entry;
+	struct drm_master *master = top;
+
+	lockdep_assert_held(&top->dev->mode_config.idr_mutex);
+
+	/*
+	 * Walk the tree starting at 'top' emptying all leases. Because
+	 * the tree is fully connected, we can do this without recursing
+	 */
+	for (;;) {
+		DRM_DEBUG_LEASE("revoke leases for %p %d\n", master, master->lessee_id);
+
+		/* Evacuate the lease */
+		idr_for_each_entry(&master->leases, entry, object)
+			idr_remove(&master->leases, object);
+
+		/* Depth-first list walk */
+
+		/* Down */
+		if (!list_empty(&master->lessees)) {
+			master = list_first_entry(&master->lessees, struct drm_master, lessee_list);
+		} else {
+			/* Up */
+			while (master != top && master == list_last_entry(&master->lessor->lessees, struct drm_master, lessee_list))
+				master = master->lessor;
+
+			if (master == top)
+				break;
+
+			/* Over */
+			master = list_entry(master->lessee_list.next, struct drm_master, lessee_list);
+		}
+	}
+}
+
+/**
+ * drm_lease_revoke - revoke access to all leased objects (idr_mutex not held)
+ * @top: the master losing its lease
+ */
+void drm_lease_revoke(struct drm_master *top)
+{
+	mutex_lock(&top->dev->mode_config.idr_mutex);
+	_drm_lease_revoke(top);
+	mutex_unlock(&top->dev->mode_config.idr_mutex);
+}

include/drm/drm_auth.h

@@ -52,6 +52,12 @@ struct drm_lock_data {
  * @dev: Link back to the DRM device
  * @lock: DRI1 lock information.
  * @driver_priv: Pointer to driver-private information.
+ * @lessor: Lease holder
+ * @lessee_id: id for lessees. Owners always have id 0
+ * @lessee_list: other lessees of the same master
+ * @lessees: drm_masters leasing from this one
+ * @leases: Objects leased to this drm_master.
+ * @lessee_idr: All lessees under this owner (only used where lessor == NULL)
  *
  * Note that master structures are only relevant for the legacy/primary device
  * nodes, hence there can only be one per device, not one per drm_minor.
@@ -76,10 +82,25 @@ struct drm_master {
 	struct idr magic_map;
 	struct drm_lock_data lock;
 	void *driver_priv;
+
+	/* Tree of display resource leases, each of which is a drm_master struct
+	 * All of these get activated simultaneously, so drm_device master points
+	 * at the top of the tree (for which lessor is NULL). Protected by
+	 * &drm_device.mode_config.idr_mutex.
+	 */
+
+	struct drm_master *lessor;
+	int	lessee_id;
+	struct list_head lessee_list;
+	struct list_head lessees;
+	struct idr leases;
+	struct idr lessee_idr;
 };
 
 struct drm_master *drm_master_get(struct drm_master *master);
 void drm_master_put(struct drm_master **master);
 bool drm_is_current_master(struct drm_file *fpriv);
 
+struct drm_master *drm_master_create(struct drm_device *dev);
+
 #endif

include/drm/drm_lease.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright © 2017 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#ifndef _DRM_LEASE_H_
+#define _DRM_LEASE_H_
+
+struct drm_file;
+struct drm_device;
+struct drm_master;
+
+struct drm_master *drm_lease_owner(struct drm_master *master);
+
+void drm_lease_destroy(struct drm_master *lessee);
+
+bool drm_lease_held(struct drm_file *file_priv, int id);
+
+bool _drm_lease_held(struct drm_file *file_priv, int id);
+
+void drm_lease_revoke(struct drm_master *master);
+
+uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs);
+
+uint32_t drm_lease_filter_encoders(struct drm_file *file_priv, uint32_t encoders);
+
+#endif /* _DRM_LEASE_H_ */

include/drm/drm_mode_object.h

@@ -24,6 +24,7 @@
 #define __DRM_MODESET_H__
 
 #include <linux/kref.h>
+#include <drm/drm_lease.h>
 struct drm_object_properties;
 struct drm_property;
 struct drm_device;