/*
 * VMware VMCI Driver
 *
 * Copyright (C) 2012 VMware, Inc. All rights reserved.
 *
 * 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 version 2 and no 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 <linux/vmw_vmci_defs.h>
#include <linux/vmw_vmci_api.h>
#include <linux/completion.h>
#include <linux/hash.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/slab.h>

#include "vmci_datagram.h"
#include "vmci_doorbell.h"
#include "vmci_resource.h"
#include "vmci_driver.h"
#include "vmci_route.h"


#define VMCI_DOORBELL_INDEX_BITS        6
#define VMCI_DOORBELL_INDEX_TABLE_SIZE  (1 << VMCI_DOORBELL_INDEX_BITS)
#define VMCI_DOORBELL_HASH(_idx)        hash_32(_idx, VMCI_DOORBELL_INDEX_BITS)

/*
 * DoorbellEntry describes the a doorbell notification handle allocated by the
 * host.
 */
struct dbell_entry {
        struct vmci_resource resource;
        struct hlist_node node;
        struct work_struct work;
        vmci_callback notify_cb;
        void *client_data;
        u32 idx;
        u32 priv_flags;
        bool run_delayed;
        atomic_t active;        /* Only used by guest personality */
};

/* The VMCI index table keeps track of currently registered doorbells. */
struct dbell_index_table {
        spinlock_t lock;        /* Index table lock */
        struct hlist_head entries[VMCI_DOORBELL_INDEX_TABLE_SIZE];
};

static struct dbell_index_table vmci_doorbell_it = {
        .lock = __SPIN_LOCK_UNLOCKED(vmci_doorbell_it.lock),
};

/*
 * The max_notify_idx is one larger than the currently known bitmap index in
 * use, and is used to determine how much of the bitmap needs to be scanned.
 */
static u32 max_notify_idx;

/*
 * The notify_idx_count is used for determining whether there are free entries
 * within the bitmap (if notify_idx_count + 1 < max_notify_idx).
 */
static u32 notify_idx_count;

/*
 * The last_notify_idx_reserved is used to track the last index handed out - in
 * the case where multiple handles share a notification index, we hand out
 * indexes round robin based on last_notify_idx_reserved.
 */
static u32 last_notify_idx_reserved;

/* This is a one entry cache used to by the index allocation. */
static u32 last_notify_idx_released = PAGE_SIZE;


/*
 * Utility function that retrieves the privilege flags associated
 * with a given doorbell handle. For guest endpoints, the
 * privileges are determined by the context ID, but for host
 * endpoints privileges are associated with the complete
 * handle. Hypervisor endpoints are not yet supported.
 */
int vmci_dbell_get_priv_flags(struct vmci_handle handle, u32 *priv_flags)
{
        if (priv_flags == NULL || handle.context == VMCI_INVALID_ID)
                return VMCI_ERROR_INVALID_ARGS;

        if (handle.context == VMCI_HOST_CONTEXT_ID) {
                struct dbell_entry *entry;
                struct vmci_resource *resource;

                resource = vmci_resource_by_handle(handle,
                                                   VMCI_RESOURCE_TYPE_DOORBELL);
                if (!resource)
                        return VMCI_ERROR_NOT_FOUND;

                entry = container_of(resource, struct dbell_entry, resource);
                *priv_flags = entry->priv_flags;
                vmci_resource_put(resource);
        } else if (handle.context == VMCI_HYPERVISOR_CONTEXT_ID) {
                /*
                 * Hypervisor endpoints for notifications are not
                 * supported (yet).
                 */
                return VMCI_ERROR_INVALID_ARGS;
        } else {
                *priv_flags = vmci_context_get_priv_flags(handle.context);
        }

        return VMCI_SUCCESS;
}

/*
 * Find doorbell entry by bitmap index.
 */
static struct dbell_entry *dbell_index_table_find(u32 idx)
{
        u32 bucket = VMCI_DOORBELL_HASH(idx);
        struct dbell_entry *dbell;

        hlist_for_each_entry(dbell, &vmci_doorbell_it.entries[bucket],
                             node) {
                if (idx == dbell->idx)
                        return dbell;
        }

        return NULL;
}

/*
 * Add the given entry to the index table.  This willi take a reference to the
 * entry's resource so that the entry is not deleted before it is removed from
 * the * table.
 */
static void dbell_index_table_add(struct dbell_entry *entry)
{
        u32 bucket;
        u32 new_notify_idx;

        vmci_resource_get(&entry->resource);

        spin_lock_bh(&vmci_doorbell_it.lock);

        /*
         * Below we try to allocate an index in the notification
         * bitmap with "not too much" sharing between resources. If we
         * use less that the full bitmap, we either add to the end if
         * there are no unused flags within the currently used area,
         * or we search for unused ones. If we use the full bitmap, we
         * allocate the index round robin.
         */
        if (max_notify_idx < PAGE_SIZE || notify_idx_count < PAGE_SIZE) {
                if (last_notify_idx_released < max_notify_idx &&
                    !dbell_index_table_find(last_notify_idx_released)) {
                        new_notify_idx = last_notify_idx_released;
                        last_notify_idx_released = PAGE_SIZE;
                } else {
                        bool reused = false;
                        new_notify_idx = last_notify_idx_reserved;
                        if (notify_idx_count + 1 < max_notify_idx) {
                                do {
                                        if (!dbell_index_table_find
                                            (new_notify_idx)) {
                                                reused = true;
                                                break;
                                        }
                                        new_notify_idx = (new_notify_idx + 1) %
                                            max_notify_idx;
                                } while (new_notify_idx !=
                                         last_notify_idx_released);
                        }
                        if (!reused) {
                                new_notify_idx = max_notify_idx;
                                max_notify_idx++;
                        }
                }
        } else {
                new_notify_idx = (last_notify_idx_reserved + 1) % PAGE_SIZE;
        }

        last_notify_idx_reserved = new_notify_idx;
        notify_idx_count++;

        entry->idx = new_notify_idx;
        bucket = VMCI_DOORBELL_HASH(entry->idx);
        hlist_add_head(&entry->node, &vmci_doorbell_it.entries[bucket]);

        spin_unlock_bh(&vmci_doorbell_it.lock);
}

/*
 * Remove the given entry from the index table.  This will release() the
 * entry's resource.
 */
static void dbell_index_table_remove(struct dbell_entry *entry)
{
        spin_lock_bh(&vmci_doorbell_it.lock);

        hlist_del_init(&entry->node);

        notify_idx_count--;
        if (entry->idx == max_notify_idx - 1) {
                /*
                 * If we delete an entry with the maximum known
                 * notification index, we take the opportunity to
                 * prune the current max. As there might be other
                 * unused indices immediately below, we lower the
                 * maximum until we hit an index in use.
                 */
                while (max_notify_idx > 0 &&
                       !dbell_index_table_find(max_notify_idx - 1))
                        max_notify_idx--;
        }

        last_notify_idx_released = entry->idx;

        spin_unlock_bh(&vmci_doorbell_it.lock);

        vmci_resource_put(&entry->resource);
}

/*
 * Creates a link between the given doorbell handle and the given
 * index in the bitmap in the device backend. A notification state
 * is created in hypervisor.
 */
static int dbell_link(struct vmci_handle handle, u32 notify_idx)
{
        struct vmci_doorbell_link_msg link_msg;

        link_msg.hdr.dst = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                            VMCI_DOORBELL_LINK);
        link_msg.hdr.src = VMCI_ANON_SRC_HANDLE;
        link_msg.hdr.payload_size = sizeof(link_msg) - VMCI_DG_HEADERSIZE;
        link_msg.handle = handle;
        link_msg.notify_idx = notify_idx;

        return vmci_send_datagram(&link_msg.hdr);
}

/*
 * Unlinks the given doorbell handle from an index in the bitmap in
 * the device backend. The notification state is destroyed in hypervisor.
 */
static int dbell_unlink(struct vmci_handle handle)
{
        struct vmci_doorbell_unlink_msg unlink_msg;

        unlink_msg.hdr.dst = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                              VMCI_DOORBELL_UNLINK);
        unlink_msg.hdr.src = VMCI_ANON_SRC_HANDLE;
        unlink_msg.hdr.payload_size = sizeof(unlink_msg) - VMCI_DG_HEADERSIZE;
        unlink_msg.handle = handle;

        return vmci_send_datagram(&unlink_msg.hdr);
}

/*
 * Notify another guest or the host.  We send a datagram down to the
 * host via the hypervisor with the notification info.
 */
static int dbell_notify_as_guest(struct vmci_handle handle, u32 priv_flags)
{
        struct vmci_doorbell_notify_msg notify_msg;

        notify_msg.hdr.dst = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                              VMCI_DOORBELL_NOTIFY);
        notify_msg.hdr.src = VMCI_ANON_SRC_HANDLE;
        notify_msg.hdr.payload_size = sizeof(notify_msg) - VMCI_DG_HEADERSIZE;
        notify_msg.handle = handle;

        return vmci_send_datagram(&notify_msg.hdr);
}

/*
 * Calls the specified callback in a delayed context.
 */
static void dbell_delayed_dispatch(struct work_struct *work)
{
        struct dbell_entry *entry = container_of(work,
                                                 struct dbell_entry, work);

        entry->notify_cb(entry->client_data);
        vmci_resource_put(&entry->resource);
}

/*
 * Dispatches a doorbell notification to the host context.
 */
int vmci_dbell_host_context_notify(u32 src_cid, struct vmci_handle handle)
{
        struct dbell_entry *entry;
        struct vmci_resource *resource;

        if (vmci_handle_is_invalid(handle)) {
                pr_devel("Notifying an invalid doorbell (handle=0x%x:0x%x)\n",
                         handle.context, handle.resource);
                return VMCI_ERROR_INVALID_ARGS;
        }

        resource = vmci_resource_by_handle(handle,
                                           VMCI_RESOURCE_TYPE_DOORBELL);
        if (!resource) {
                pr_devel("Notifying an unknown doorbell (handle=0x%x:0x%x)\n",
                         handle.context, handle.resource);
                return VMCI_ERROR_NOT_FOUND;
        }

        entry = container_of(resource, struct dbell_entry, resource);
        if (entry->run_delayed) {
                schedule_work(&entry->work);
        } else {
                entry->notify_cb(entry->client_data);
                vmci_resource_put(resource);
        }

        return VMCI_SUCCESS;
}

/*
 * Register the notification bitmap with the host.
 */
bool vmci_dbell_register_notification_bitmap(u32 bitmap_ppn)
{
        int result;
        struct vmci_notify_bm_set_msg bitmap_set_msg;

        bitmap_set_msg.hdr.dst = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                                  VMCI_SET_NOTIFY_BITMAP);
        bitmap_set_msg.hdr.src = VMCI_ANON_SRC_HANDLE;
        bitmap_set_msg.hdr.payload_size = sizeof(bitmap_set_msg) -
            VMCI_DG_HEADERSIZE;
        bitmap_set_msg.bitmap_ppn = bitmap_ppn;

        result = vmci_send_datagram(&bitmap_set_msg.hdr);
        if (result != VMCI_SUCCESS) {
                pr_devel("Failed to register (PPN=%u) as notification bitmap (error=%d)\n",
                         bitmap_ppn, result);
                return false;
        }
        return true;
}

/*
 * Executes or schedules the handlers for a given notify index.
 */
static void dbell_fire_entries(u32 notify_idx)
{
        u32 bucket = VMCI_DOORBELL_HASH(notify_idx);
        struct dbell_entry *dbell;

        spin_lock_bh(&vmci_doorbell_it.lock);

        hlist_for_each_entry(dbell, &vmci_doorbell_it.entries[bucket], node) {
                if (dbell->idx == notify_idx &&
                    atomic_read(&dbell->active) == 1) {
                        if (dbell->run_delayed) {
                                vmci_resource_get(&dbell->resource);
                                schedule_work(&dbell->work);
                        } else {
                                dbell->notify_cb(dbell->client_data);
                        }
                }
        }

        spin_unlock_bh(&vmci_doorbell_it.lock);
}

/*
 * Scans the notification bitmap, collects pending notifications,
 * resets the bitmap and invokes appropriate callbacks.
 */
void vmci_dbell_scan_notification_entries(u8 *bitmap)
{
        u32 idx;

        for (idx = 0; idx < max_notify_idx; idx++) {
                if (bitmap[idx] & 0x1) {
                        bitmap[idx] &= ~1;
                        dbell_fire_entries(idx);
                }
        }
}

/*
 * vmci_doorbell_create() - Creates a doorbell
 * @handle:     A handle used to track the resource.  Can be invalid.
 * @flags:      Flag that determines context of callback.
 * @priv_flags: Privileges flags.
 * @notify_cb:  The callback to be ivoked when the doorbell fires.
 * @client_data:        A parameter to be passed to the callback.
 *
 * Creates a doorbell with the given callback. If the handle is
 * VMCI_INVALID_HANDLE, a free handle will be assigned, if
 * possible. The callback can be run immediately (potentially with
 * locks held - the default) or delayed (in a kernel thread) by
 * specifying the flag VMCI_FLAG_DELAYED_CB. If delayed execution
 * is selected, a given callback may not be run if the kernel is
 * unable to allocate memory for the delayed execution (highly
 * unlikely).
 */
int vmci_doorbell_create(struct vmci_handle *handle,
                         u32 flags,
                         u32 priv_flags,
                         vmci_callback notify_cb, void *client_data)
{
        struct dbell_entry *entry;
        struct vmci_handle new_handle;
        int result;

        if (!handle || !notify_cb || flags & ~VMCI_FLAG_DELAYED_CB ||
            priv_flags & ~VMCI_PRIVILEGE_ALL_FLAGS)
                return VMCI_ERROR_INVALID_ARGS;

        entry = kmalloc(sizeof(*entry), GFP_KERNEL);
        if (entry == NULL) {
                pr_warn("Failed allocating memory for datagram entry\n");
                return VMCI_ERROR_NO_MEM;
        }

        if (vmci_handle_is_invalid(*handle)) {
                u32 context_id = vmci_get_context_id();

                /* Let resource code allocate a free ID for us */
                new_handle = vmci_make_handle(context_id, VMCI_INVALID_ID);
        } else {
                bool valid_context = false;

                /*
                 * Validate the handle.  We must do both of the checks below
                 * because we can be acting as both a host and a guest at the
                 * same time. We always allow the host context ID, since the
                 * host functionality is in practice always there with the
                 * unified driver.
                 */
                if (handle->context == VMCI_HOST_CONTEXT_ID ||
                    (vmci_guest_code_active() &&
                     vmci_get_context_id() == handle->context)) {
                        valid_context = true;
                }

                if (!valid_context || handle->resource == VMCI_INVALID_ID) {
                        pr_devel("Invalid argument (handle=0x%x:0x%x)\n",
                                 handle->context, handle->resource);
                        result = VMCI_ERROR_INVALID_ARGS;
                        goto free_mem;
                }

                new_handle = *handle;
        }

        entry->idx = 0;
        INIT_HLIST_NODE(&entry->node);
        entry->priv_flags = priv_flags;
        INIT_WORK(&entry->work, dbell_delayed_dispatch);
        entry->run_delayed = flags & VMCI_FLAG_DELAYED_CB;
        entry->notify_cb = notify_cb;
        entry->client_data = client_data;
        atomic_set(&entry->active, 0);

        result = vmci_resource_add(&entry->resource,
                                   VMCI_RESOURCE_TYPE_DOORBELL,
                                   new_handle);
        if (result != VMCI_SUCCESS) {
                pr_warn("Failed to add new resource (handle=0x%x:0x%x), error: %d\n",
                        new_handle.context, new_handle.resource, result);
                goto free_mem;
        }

        new_handle = vmci_resource_handle(&entry->resource);
        if (vmci_guest_code_active()) {
                dbell_index_table_add(entry);
                result = dbell_link(new_handle, entry->idx);
                if (VMCI_SUCCESS != result)
                        goto destroy_resource;

                atomic_set(&entry->active, 1);
        }

        *handle = new_handle;

        return result;

 destroy_resource:
        dbell_index_table_remove(entry);
        vmci_resource_remove(&entry->resource);
 free_mem:
        kfree(entry);
        return result;
}
EXPORT_SYMBOL_GPL(vmci_doorbell_create);

/*
 * vmci_doorbell_destroy() - Destroy a doorbell.
 * @handle:     The handle tracking the resource.
 *
 * Destroys a doorbell previously created with vmcii_doorbell_create. This
 * operation may block waiting for a callback to finish.
 */
int vmci_doorbell_destroy(struct vmci_handle handle)
{
        struct dbell_entry *entry;
        struct vmci_resource *resource;

        if (vmci_handle_is_invalid(handle))
                return VMCI_ERROR_INVALID_ARGS;

        resource = vmci_resource_by_handle(handle,
                                           VMCI_RESOURCE_TYPE_DOORBELL);
        if (!resource) {
                pr_devel("Failed to destroy doorbell (handle=0x%x:0x%x)\n",
                         handle.context, handle.resource);
                return VMCI_ERROR_NOT_FOUND;
        }

        entry = container_of(resource, struct dbell_entry, resource);

        if (vmci_guest_code_active()) {
                int result;

                dbell_index_table_remove(entry);

                result = dbell_unlink(handle);
                if (VMCI_SUCCESS != result) {

                        /*
                         * The only reason this should fail would be
                         * an inconsistency between guest and
                         * hypervisor state, where the guest believes
                         * it has an active registration whereas the
                         * hypervisor doesn't. One case where this may
                         * happen is if a doorbell is unregistered
                         * following a hibernation at a time where the
                         * doorbell state hasn't been restored on the
                         * hypervisor side yet. Since the handle has
                         * now been removed in the guest, we just
                         * print a warning and return success.
                         */
                        pr_devel("Unlink of doorbell (handle=0x%x:0x%x) unknown by hypervisor (error=%d)\n",
                                 handle.context, handle.resource, result);
                }
        }

        /*
         * Now remove the resource from the table.  It might still be in use
         * after this, in a callback or still on the delayed work queue.
         */
        vmci_resource_put(&entry->resource);
        vmci_resource_remove(&entry->resource);

        kfree(entry);

        return VMCI_SUCCESS;
}
EXPORT_SYMBOL_GPL(vmci_doorbell_destroy);

/*
 * vmci_doorbell_notify() - Ring the doorbell (and hide in the bushes).
 * @dst:        The handlle identifying the doorbell resource
 * @priv_flags: Priviledge flags.
 *
 * Generates a notification on the doorbell identified by the
 * handle. For host side generation of notifications, the caller
 * can specify what the privilege of the calling side is.
 */
int vmci_doorbell_notify(struct vmci_handle dst, u32 priv_flags)
{
        int retval;
        enum vmci_route route;
        struct vmci_handle src;

        if (vmci_handle_is_invalid(dst) ||
            (priv_flags & ~VMCI_PRIVILEGE_ALL_FLAGS))
                return VMCI_ERROR_INVALID_ARGS;

        src = VMCI_INVALID_HANDLE;
        retval = vmci_route(&src, &dst, false, &route);
        if (retval < VMCI_SUCCESS)
                return retval;

        if (VMCI_ROUTE_AS_HOST == route)
                return vmci_ctx_notify_dbell(VMCI_HOST_CONTEXT_ID,
                                             dst, priv_flags);

        if (VMCI_ROUTE_AS_GUEST == route)
                return dbell_notify_as_guest(dst, priv_flags);

        pr_warn("Unknown route (%d) for doorbell\n", route);
        return VMCI_ERROR_DST_UNREACHABLE;
}
EXPORT_SYMBOL_GPL(vmci_doorbell_notify);