use less confusing names for iov_iter direction initializers

[linux-block.git] / drivers / misc / vmw_vmci / vmci_queue_pair.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * VMware VMCI Driver
 *
 * Copyright (C) 2012 VMware, Inc. All rights reserved.
 */

#include <linux/vmw_vmci_defs.h>
#include <linux/vmw_vmci_api.h>
#include <linux/highmem.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/pagemap.h>
#include <linux/pci.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/uio.h>
#include <linux/wait.h>
#include <linux/vmalloc.h>
#include <linux/skbuff.h>

#include "vmci_handle_array.h"
#include "vmci_queue_pair.h"
#include "vmci_datagram.h"
#include "vmci_resource.h"
#include "vmci_context.h"
#include "vmci_driver.h"
#include "vmci_event.h"
#include "vmci_route.h"

/*
 * In the following, we will distinguish between two kinds of VMX processes -
 * the ones with versions lower than VMCI_VERSION_NOVMVM that use specialized
 * VMCI page files in the VMX and supporting VM to VM communication and the
 * newer ones that use the guest memory directly. We will in the following
 * refer to the older VMX versions as old-style VMX'en, and the newer ones as
 * new-style VMX'en.
 *
 * The state transition datagram is as follows (the VMCIQPB_ prefix has been
 * removed for readability) - see below for more details on the transtions:
 *
 *            --------------  NEW  -------------
 *            |                                |
 *           \_/                              \_/
 *     CREATED_NO_MEM <-----------------> CREATED_MEM
 *            |    |                           |
 *            |    o-----------------------o   |
 *            |                            |   |
 *           \_/                          \_/ \_/
 *     ATTACHED_NO_MEM <----------------> ATTACHED_MEM
 *            |                            |   |
 *            |     o----------------------o   |
 *            |     |                          |
 *           \_/   \_/                        \_/
 *     SHUTDOWN_NO_MEM <----------------> SHUTDOWN_MEM
 *            |                                |
 *            |                                |
 *            -------------> gone <-------------
 *
 * In more detail. When a VMCI queue pair is first created, it will be in the
 * VMCIQPB_NEW state. It will then move into one of the following states:
 *
 * - VMCIQPB_CREATED_NO_MEM: this state indicates that either:
 *
 *     - the created was performed by a host endpoint, in which case there is
 *       no backing memory yet.
 *
 *     - the create was initiated by an old-style VMX, that uses
 *       vmci_qp_broker_set_page_store to specify the UVAs of the queue pair at
 *       a later point in time. This state can be distinguished from the one
 *       above by the context ID of the creator. A host side is not allowed to
 *       attach until the page store has been set.
 *
 * - VMCIQPB_CREATED_MEM: this state is the result when the queue pair
 *     is created by a VMX using the queue pair device backend that
 *     sets the UVAs of the queue pair immediately and stores the
 *     information for later attachers. At this point, it is ready for
 *     the host side to attach to it.
 *
 * Once the queue pair is in one of the created states (with the exception of
 * the case mentioned for older VMX'en above), it is possible to attach to the
 * queue pair. Again we have two new states possible:
 *
 * - VMCIQPB_ATTACHED_MEM: this state can be reached through the following
 *   paths:
 *
 *     - from VMCIQPB_CREATED_NO_MEM when a new-style VMX allocates a queue
 *       pair, and attaches to a queue pair previously created by the host side.
 *
 *     - from VMCIQPB_CREATED_MEM when the host side attaches to a queue pair
 *       already created by a guest.
 *
 *     - from VMCIQPB_ATTACHED_NO_MEM, when an old-style VMX calls
 *       vmci_qp_broker_set_page_store (see below).
 *
 * - VMCIQPB_ATTACHED_NO_MEM: If the queue pair already was in the
 *     VMCIQPB_CREATED_NO_MEM due to a host side create, an old-style VMX will
 *     bring the queue pair into this state. Once vmci_qp_broker_set_page_store
 *     is called to register the user memory, the VMCIQPB_ATTACH_MEM state
 *     will be entered.
 *
 * From the attached queue pair, the queue pair can enter the shutdown states
 * when either side of the queue pair detaches. If the guest side detaches
 * first, the queue pair will enter the VMCIQPB_SHUTDOWN_NO_MEM state, where
 * the content of the queue pair will no longer be available. If the host
 * side detaches first, the queue pair will either enter the
 * VMCIQPB_SHUTDOWN_MEM, if the guest memory is currently mapped, or
 * VMCIQPB_SHUTDOWN_NO_MEM, if the guest memory is not mapped
 * (e.g., the host detaches while a guest is stunned).
 *
 * New-style VMX'en will also unmap guest memory, if the guest is
 * quiesced, e.g., during a snapshot operation. In that case, the guest
 * memory will no longer be available, and the queue pair will transition from
 * *_MEM state to a *_NO_MEM state. The VMX may later map the memory once more,
 * in which case the queue pair will transition from the *_NO_MEM state at that
 * point back to the *_MEM state. Note that the *_NO_MEM state may have changed,
 * since the peer may have either attached or detached in the meantime. The
 * values are laid out such that ++ on a state will move from a *_NO_MEM to a
 * *_MEM state, and vice versa.
 */

/* The Kernel specific component of the struct vmci_queue structure. */
struct vmci_queue_kern_if {
        struct mutex __mutex;   /* Protects the queue. */
        struct mutex *mutex;    /* Shared by producer and consumer queues. */
        size_t num_pages;       /* Number of pages incl. header. */
        bool host;              /* Host or guest? */
        union {
                struct {
                        dma_addr_t *pas;
                        void **vas;
                } g;            /* Used by the guest. */
                struct {
                        struct page **page;
                        struct page **header_page;
                } h;            /* Used by the host. */
        } u;
};

/*
 * This structure is opaque to the clients.
 */
struct vmci_qp {
        struct vmci_handle handle;
        struct vmci_queue *produce_q;
        struct vmci_queue *consume_q;
        u64 produce_q_size;
        u64 consume_q_size;
        u32 peer;
        u32 flags;
        u32 priv_flags;
        bool guest_endpoint;
        unsigned int blocked;
        unsigned int generation;
        wait_queue_head_t event;
};

enum qp_broker_state {
        VMCIQPB_NEW,
        VMCIQPB_CREATED_NO_MEM,
        VMCIQPB_CREATED_MEM,
        VMCIQPB_ATTACHED_NO_MEM,
        VMCIQPB_ATTACHED_MEM,
        VMCIQPB_SHUTDOWN_NO_MEM,
        VMCIQPB_SHUTDOWN_MEM,
        VMCIQPB_GONE
};

#define QPBROKERSTATE_HAS_MEM(_qpb) (_qpb->state == VMCIQPB_CREATED_MEM || \
                                     _qpb->state == VMCIQPB_ATTACHED_MEM || \
                                     _qpb->state == VMCIQPB_SHUTDOWN_MEM)

/*
 * In the queue pair broker, we always use the guest point of view for
 * the produce and consume queue values and references, e.g., the
 * produce queue size stored is the guests produce queue size. The
 * host endpoint will need to swap these around. The only exception is
 * the local queue pairs on the host, in which case the host endpoint
 * that creates the queue pair will have the right orientation, and
 * the attaching host endpoint will need to swap.
 */
struct qp_entry {
        struct list_head list_item;
        struct vmci_handle handle;
        u32 peer;
        u32 flags;
        u64 produce_size;
        u64 consume_size;
        u32 ref_count;
};

struct qp_broker_entry {
        struct vmci_resource resource;
        struct qp_entry qp;
        u32 create_id;
        u32 attach_id;
        enum qp_broker_state state;
        bool require_trusted_attach;
        bool created_by_trusted;
        bool vmci_page_files;   /* Created by VMX using VMCI page files */
        struct vmci_queue *produce_q;
        struct vmci_queue *consume_q;
        struct vmci_queue_header saved_produce_q;
        struct vmci_queue_header saved_consume_q;
        vmci_event_release_cb wakeup_cb;
        void *client_data;
        void *local_mem;        /* Kernel memory for local queue pair */
};

struct qp_guest_endpoint {
        struct vmci_resource resource;
        struct qp_entry qp;
        u64 num_ppns;
        void *produce_q;
        void *consume_q;
        struct ppn_set ppn_set;
};

struct qp_list {
        struct list_head head;
        struct mutex mutex;     /* Protect queue list. */
};

static struct qp_list qp_broker_list = {
        .head = LIST_HEAD_INIT(qp_broker_list.head),
        .mutex = __MUTEX_INITIALIZER(qp_broker_list.mutex),
};

static struct qp_list qp_guest_endpoints = {
        .head = LIST_HEAD_INIT(qp_guest_endpoints.head),
        .mutex = __MUTEX_INITIALIZER(qp_guest_endpoints.mutex),
};

#define INVALID_VMCI_GUEST_MEM_ID  0
#define QPE_NUM_PAGES(_QPE) ((u32) \
                             (DIV_ROUND_UP(_QPE.produce_size, PAGE_SIZE) + \
                              DIV_ROUND_UP(_QPE.consume_size, PAGE_SIZE) + 2))
#define QP_SIZES_ARE_VALID(_prod_qsize, _cons_qsize) \
        ((_prod_qsize) + (_cons_qsize) >= max(_prod_qsize, _cons_qsize) && \
         (_prod_qsize) + (_cons_qsize) <= VMCI_MAX_GUEST_QP_MEMORY)

/*
 * Frees kernel VA space for a given queue and its queue header, and
 * frees physical data pages.
 */
static void qp_free_queue(void *q, u64 size)
{
        struct vmci_queue *queue = q;

        if (queue) {
                u64 i;

                /* Given size does not include header, so add in a page here. */
                for (i = 0; i < DIV_ROUND_UP(size, PAGE_SIZE) + 1; i++) {
                        dma_free_coherent(&vmci_pdev->dev, PAGE_SIZE,
                                          queue->kernel_if->u.g.vas[i],
                                          queue->kernel_if->u.g.pas[i]);
                }

                vfree(queue);
        }
}

/*
 * Allocates kernel queue pages of specified size with IOMMU mappings,
 * plus space for the queue structure/kernel interface and the queue
 * header.
 */
static void *qp_alloc_queue(u64 size, u32 flags)
{
        u64 i;
        struct vmci_queue *queue;
        size_t pas_size;
        size_t vas_size;
        size_t queue_size = sizeof(*queue) + sizeof(*queue->kernel_if);
        u64 num_pages;

        if (size > SIZE_MAX - PAGE_SIZE)
                return NULL;
        num_pages = DIV_ROUND_UP(size, PAGE_SIZE) + 1;
        if (num_pages >
                 (SIZE_MAX - queue_size) /
                 (sizeof(*queue->kernel_if->u.g.pas) +
                  sizeof(*queue->kernel_if->u.g.vas)))
                return NULL;

        pas_size = num_pages * sizeof(*queue->kernel_if->u.g.pas);
        vas_size = num_pages * sizeof(*queue->kernel_if->u.g.vas);
        queue_size += pas_size + vas_size;

        queue = vmalloc(queue_size);
        if (!queue)
                return NULL;

        queue->q_header = NULL;
        queue->saved_header = NULL;
        queue->kernel_if = (struct vmci_queue_kern_if *)(queue + 1);
        queue->kernel_if->mutex = NULL;
        queue->kernel_if->num_pages = num_pages;
        queue->kernel_if->u.g.pas = (dma_addr_t *)(queue->kernel_if + 1);
        queue->kernel_if->u.g.vas =
                (void **)((u8 *)queue->kernel_if->u.g.pas + pas_size);
        queue->kernel_if->host = false;

        for (i = 0; i < num_pages; i++) {
                queue->kernel_if->u.g.vas[i] =
                        dma_alloc_coherent(&vmci_pdev->dev, PAGE_SIZE,
                                           &queue->kernel_if->u.g.pas[i],
                                           GFP_KERNEL);
                if (!queue->kernel_if->u.g.vas[i]) {
                        /* Size excl. the header. */
                        qp_free_queue(queue, i * PAGE_SIZE);
                        return NULL;
                }
        }

        /* Queue header is the first page. */
        queue->q_header = queue->kernel_if->u.g.vas[0];

        return queue;
}

/*
 * Copies from a given buffer or iovector to a VMCI Queue.  Uses
 * kmap_local_page() to dynamically map required portions of the queue
 * by traversing the offset -> page translation structure for the queue.
 * Assumes that offset + size does not wrap around in the queue.
 */
static int qp_memcpy_to_queue_iter(struct vmci_queue *queue,
                                  u64 queue_offset,
                                  struct iov_iter *from,
                                  size_t size)
{
        struct vmci_queue_kern_if *kernel_if = queue->kernel_if;
        size_t bytes_copied = 0;

        while (bytes_copied < size) {
                const u64 page_index =
                        (queue_offset + bytes_copied) / PAGE_SIZE;
                const size_t page_offset =
                    (queue_offset + bytes_copied) & (PAGE_SIZE - 1);
                void *va;
                size_t to_copy;

                if (kernel_if->host)
                        va = kmap_local_page(kernel_if->u.h.page[page_index]);
                else
                        va = kernel_if->u.g.vas[page_index + 1];
                        /* Skip header. */

                if (size - bytes_copied > PAGE_SIZE - page_offset)
                        /* Enough payload to fill up from this page. */
                        to_copy = PAGE_SIZE - page_offset;
                else
                        to_copy = size - bytes_copied;

                if (!copy_from_iter_full((u8 *)va + page_offset, to_copy,
                                         from)) {
                        if (kernel_if->host)
                                kunmap_local(va);
                        return VMCI_ERROR_INVALID_ARGS;
                }
                bytes_copied += to_copy;
                if (kernel_if->host)
                        kunmap_local(va);
        }

        return VMCI_SUCCESS;
}

/*
 * Copies to a given buffer or iovector from a VMCI Queue.  Uses
 * kmap_local_page() to dynamically map required portions of the queue
 * by traversing the offset -> page translation structure for the queue.
 * Assumes that offset + size does not wrap around in the queue.
 */
static int qp_memcpy_from_queue_iter(struct iov_iter *to,
                                    const struct vmci_queue *queue,
                                    u64 queue_offset, size_t size)
{
        struct vmci_queue_kern_if *kernel_if = queue->kernel_if;
        size_t bytes_copied = 0;

        while (bytes_copied < size) {
                const u64 page_index =
                        (queue_offset + bytes_copied) / PAGE_SIZE;
                const size_t page_offset =
                    (queue_offset + bytes_copied) & (PAGE_SIZE - 1);
                void *va;
                size_t to_copy;
                int err;

                if (kernel_if->host)
                        va = kmap_local_page(kernel_if->u.h.page[page_index]);
                else
                        va = kernel_if->u.g.vas[page_index + 1];
                        /* Skip header. */

                if (size - bytes_copied > PAGE_SIZE - page_offset)
                        /* Enough payload to fill up this page. */
                        to_copy = PAGE_SIZE - page_offset;
                else
                        to_copy = size - bytes_copied;

                err = copy_to_iter((u8 *)va + page_offset, to_copy, to);
                if (err != to_copy) {
                        if (kernel_if->host)
                                kunmap_local(va);
                        return VMCI_ERROR_INVALID_ARGS;
                }
                bytes_copied += to_copy;
                if (kernel_if->host)
                        kunmap_local(va);
        }

        return VMCI_SUCCESS;
}

/*
 * Allocates two list of PPNs --- one for the pages in the produce queue,
 * and the other for the pages in the consume queue. Intializes the list
 * of PPNs with the page frame numbers of the KVA for the two queues (and
 * the queue headers).
 */
static int qp_alloc_ppn_set(void *prod_q,
                            u64 num_produce_pages,
                            void *cons_q,
                            u64 num_consume_pages, struct ppn_set *ppn_set)
{
        u64 *produce_ppns;
        u64 *consume_ppns;
        struct vmci_queue *produce_q = prod_q;
        struct vmci_queue *consume_q = cons_q;
        u64 i;

        if (!produce_q || !num_produce_pages || !consume_q ||
            !num_consume_pages || !ppn_set)
                return VMCI_ERROR_INVALID_ARGS;

        if (ppn_set->initialized)
                return VMCI_ERROR_ALREADY_EXISTS;

        produce_ppns =
            kmalloc_array(num_produce_pages, sizeof(*produce_ppns),
                          GFP_KERNEL);
        if (!produce_ppns)
                return VMCI_ERROR_NO_MEM;

        consume_ppns =
            kmalloc_array(num_consume_pages, sizeof(*consume_ppns),
                          GFP_KERNEL);
        if (!consume_ppns) {
                kfree(produce_ppns);
                return VMCI_ERROR_NO_MEM;
        }

        for (i = 0; i < num_produce_pages; i++)
                produce_ppns[i] =
                        produce_q->kernel_if->u.g.pas[i] >> PAGE_SHIFT;

        for (i = 0; i < num_consume_pages; i++)
                consume_ppns[i] =
                        consume_q->kernel_if->u.g.pas[i] >> PAGE_SHIFT;

        ppn_set->num_produce_pages = num_produce_pages;
        ppn_set->num_consume_pages = num_consume_pages;
        ppn_set->produce_ppns = produce_ppns;
        ppn_set->consume_ppns = consume_ppns;
        ppn_set->initialized = true;
        return VMCI_SUCCESS;
}

/*
 * Frees the two list of PPNs for a queue pair.
 */
static void qp_free_ppn_set(struct ppn_set *ppn_set)
{
        if (ppn_set->initialized) {
                /* Do not call these functions on NULL inputs. */
                kfree(ppn_set->produce_ppns);
                kfree(ppn_set->consume_ppns);
        }
        memset(ppn_set, 0, sizeof(*ppn_set));
}

/*
 * Populates the list of PPNs in the hypercall structure with the PPNS
 * of the produce queue and the consume queue.
 */
static int qp_populate_ppn_set(u8 *call_buf, const struct ppn_set *ppn_set)
{
        if (vmci_use_ppn64()) {
                memcpy(call_buf, ppn_set->produce_ppns,
                       ppn_set->num_produce_pages *
                       sizeof(*ppn_set->produce_ppns));
                memcpy(call_buf +
                       ppn_set->num_produce_pages *
                       sizeof(*ppn_set->produce_ppns),
                       ppn_set->consume_ppns,
                       ppn_set->num_consume_pages *
                       sizeof(*ppn_set->consume_ppns));
        } else {
                int i;
                u32 *ppns = (u32 *) call_buf;

                for (i = 0; i < ppn_set->num_produce_pages; i++)
                        ppns[i] = (u32) ppn_set->produce_ppns[i];

                ppns = &ppns[ppn_set->num_produce_pages];

                for (i = 0; i < ppn_set->num_consume_pages; i++)
                        ppns[i] = (u32) ppn_set->consume_ppns[i];
        }

        return VMCI_SUCCESS;
}

/*
 * Allocates kernel VA space of specified size plus space for the queue
 * and kernel interface.  This is different from the guest queue allocator,
 * because we do not allocate our own queue header/data pages here but
 * share those of the guest.
 */
static struct vmci_queue *qp_host_alloc_queue(u64 size)
{
        struct vmci_queue *queue;
        size_t queue_page_size;
        u64 num_pages;
        const size_t queue_size = sizeof(*queue) + sizeof(*(queue->kernel_if));

        if (size > min_t(size_t, VMCI_MAX_GUEST_QP_MEMORY, SIZE_MAX - PAGE_SIZE))
                return NULL;
        num_pages = DIV_ROUND_UP(size, PAGE_SIZE) + 1;
        if (num_pages > (SIZE_MAX - queue_size) /
                 sizeof(*queue->kernel_if->u.h.page))
                return NULL;

        queue_page_size = num_pages * sizeof(*queue->kernel_if->u.h.page);

        if (queue_size + queue_page_size > KMALLOC_MAX_SIZE)
                return NULL;

        queue = kzalloc(queue_size + queue_page_size, GFP_KERNEL);
        if (queue) {
                queue->q_header = NULL;
                queue->saved_header = NULL;
                queue->kernel_if = (struct vmci_queue_kern_if *)(queue + 1);
                queue->kernel_if->host = true;
                queue->kernel_if->mutex = NULL;
                queue->kernel_if->num_pages = num_pages;
                queue->kernel_if->u.h.header_page =
                    (struct page **)((u8 *)queue + queue_size);
                queue->kernel_if->u.h.page =
                        &queue->kernel_if->u.h.header_page[1];
        }

        return queue;
}

/*
 * Frees kernel memory for a given queue (header plus translation
 * structure).
 */
static void qp_host_free_queue(struct vmci_queue *queue, u64 queue_size)
{
        kfree(queue);
}

/*
 * Initialize the mutex for the pair of queues.  This mutex is used to
 * protect the q_header and the buffer from changing out from under any
 * users of either queue.  Of course, it's only any good if the mutexes
 * are actually acquired.  Queue structure must lie on non-paged memory
 * or we cannot guarantee access to the mutex.
 */
static void qp_init_queue_mutex(struct vmci_queue *produce_q,
                                struct vmci_queue *consume_q)
{
        /*
         * Only the host queue has shared state - the guest queues do not
         * need to synchronize access using a queue mutex.
         */

        if (produce_q->kernel_if->host) {
                produce_q->kernel_if->mutex = &produce_q->kernel_if->__mutex;
                consume_q->kernel_if->mutex = &produce_q->kernel_if->__mutex;
                mutex_init(produce_q->kernel_if->mutex);
        }
}

/*
 * Cleans up the mutex for the pair of queues.
 */
static void qp_cleanup_queue_mutex(struct vmci_queue *produce_q,
                                   struct vmci_queue *consume_q)
{
        if (produce_q->kernel_if->host) {
                produce_q->kernel_if->mutex = NULL;
                consume_q->kernel_if->mutex = NULL;
        }
}

/*
 * Acquire the mutex for the queue.  Note that the produce_q and
 * the consume_q share a mutex.  So, only one of the two need to
 * be passed in to this routine.  Either will work just fine.
 */
static void qp_acquire_queue_mutex(struct vmci_queue *queue)
{
        if (queue->kernel_if->host)
                mutex_lock(queue->kernel_if->mutex);
}

/*
 * Release the mutex for the queue.  Note that the produce_q and
 * the consume_q share a mutex.  So, only one of the two need to
 * be passed in to this routine.  Either will work just fine.
 */
static void qp_release_queue_mutex(struct vmci_queue *queue)
{
        if (queue->kernel_if->host)
                mutex_unlock(queue->kernel_if->mutex);
}

/*
 * Helper function to release pages in the PageStoreAttachInfo
 * previously obtained using get_user_pages.
 */
static void qp_release_pages(struct page **pages,
                             u64 num_pages, bool dirty)
{
        int i;

        for (i = 0; i < num_pages; i++) {
                if (dirty)
                        set_page_dirty_lock(pages[i]);

                put_page(pages[i]);
                pages[i] = NULL;
        }
}

/*
 * Lock the user pages referenced by the {produce,consume}Buffer
 * struct into memory and populate the {produce,consume}Pages
 * arrays in the attach structure with them.
 */
static int qp_host_get_user_memory(u64 produce_uva,
                                   u64 consume_uva,
                                   struct vmci_queue *produce_q,
                                   struct vmci_queue *consume_q)
{
        int retval;
        int err = VMCI_SUCCESS;

        retval = get_user_pages_fast((uintptr_t) produce_uva,
                                     produce_q->kernel_if->num_pages,
                                     FOLL_WRITE,
                                     produce_q->kernel_if->u.h.header_page);
        if (retval < (int)produce_q->kernel_if->num_pages) {
                pr_debug("get_user_pages_fast(produce) failed (retval=%d)",
                        retval);
                if (retval > 0)
                        qp_release_pages(produce_q->kernel_if->u.h.header_page,
                                        retval, false);
                err = VMCI_ERROR_NO_MEM;
                goto out;
        }

        retval = get_user_pages_fast((uintptr_t) consume_uva,
                                     consume_q->kernel_if->num_pages,
                                     FOLL_WRITE,
                                     consume_q->kernel_if->u.h.header_page);
        if (retval < (int)consume_q->kernel_if->num_pages) {
                pr_debug("get_user_pages_fast(consume) failed (retval=%d)",
                        retval);
                if (retval > 0)
                        qp_release_pages(consume_q->kernel_if->u.h.header_page,
                                        retval, false);
                qp_release_pages(produce_q->kernel_if->u.h.header_page,
                                 produce_q->kernel_if->num_pages, false);
                err = VMCI_ERROR_NO_MEM;
        }

 out:
        return err;
}

/*
 * Registers the specification of the user pages used for backing a queue
 * pair. Enough information to map in pages is stored in the OS specific
 * part of the struct vmci_queue structure.
 */
static int qp_host_register_user_memory(struct vmci_qp_page_store *page_store,
                                        struct vmci_queue *produce_q,
                                        struct vmci_queue *consume_q)
{
        u64 produce_uva;
        u64 consume_uva;

        /*
         * The new style and the old style mapping only differs in
         * that we either get a single or two UVAs, so we split the
         * single UVA range at the appropriate spot.
         */
        produce_uva = page_store->pages;
        consume_uva = page_store->pages +
            produce_q->kernel_if->num_pages * PAGE_SIZE;
        return qp_host_get_user_memory(produce_uva, consume_uva, produce_q,
                                       consume_q);
}

/*
 * Releases and removes the references to user pages stored in the attach
 * struct.  Pages are released from the page cache and may become
 * swappable again.
 */
static void qp_host_unregister_user_memory(struct vmci_queue *produce_q,
                                           struct vmci_queue *consume_q)
{
        qp_release_pages(produce_q->kernel_if->u.h.header_page,
                         produce_q->kernel_if->num_pages, true);
        memset(produce_q->kernel_if->u.h.header_page, 0,
               sizeof(*produce_q->kernel_if->u.h.header_page) *
               produce_q->kernel_if->num_pages);
        qp_release_pages(consume_q->kernel_if->u.h.header_page,
                         consume_q->kernel_if->num_pages, true);
        memset(consume_q->kernel_if->u.h.header_page, 0,
               sizeof(*consume_q->kernel_if->u.h.header_page) *
               consume_q->kernel_if->num_pages);
}

/*
 * Once qp_host_register_user_memory has been performed on a
 * queue, the queue pair headers can be mapped into the
 * kernel. Once mapped, they must be unmapped with
 * qp_host_unmap_queues prior to calling
 * qp_host_unregister_user_memory.
 * Pages are pinned.
 */
static int qp_host_map_queues(struct vmci_queue *produce_q,
                              struct vmci_queue *consume_q)
{
        int result;

        if (!produce_q->q_header || !consume_q->q_header) {
                struct page *headers[2];

                if (produce_q->q_header != consume_q->q_header)
                        return VMCI_ERROR_QUEUEPAIR_MISMATCH;

                if (produce_q->kernel_if->u.h.header_page == NULL ||
                    *produce_q->kernel_if->u.h.header_page == NULL)
                        return VMCI_ERROR_UNAVAILABLE;

                headers[0] = *produce_q->kernel_if->u.h.header_page;
                headers[1] = *consume_q->kernel_if->u.h.header_page;

                produce_q->q_header = vmap(headers, 2, VM_MAP, PAGE_KERNEL);
                if (produce_q->q_header != NULL) {
                        consume_q->q_header =
                            (struct vmci_queue_header *)((u8 *)
                                                         produce_q->q_header +
                                                         PAGE_SIZE);
                        result = VMCI_SUCCESS;
                } else {
                        pr_warn("vmap failed\n");
                        result = VMCI_ERROR_NO_MEM;
                }
        } else {
                result = VMCI_SUCCESS;
        }

        return result;
}

/*
 * Unmaps previously mapped queue pair headers from the kernel.
 * Pages are unpinned.
 */
static int qp_host_unmap_queues(u32 gid,
                                struct vmci_queue *produce_q,
                                struct vmci_queue *consume_q)
{
        if (produce_q->q_header) {
                if (produce_q->q_header < consume_q->q_header)
                        vunmap(produce_q->q_header);
                else
                        vunmap(consume_q->q_header);

                produce_q->q_header = NULL;
                consume_q->q_header = NULL;
        }

        return VMCI_SUCCESS;
}

/*
 * Finds the entry in the list corresponding to a given handle. Assumes
 * that the list is locked.
 */
static struct qp_entry *qp_list_find(struct qp_list *qp_list,
                                     struct vmci_handle handle)
{
        struct qp_entry *entry;

        if (vmci_handle_is_invalid(handle))
                return NULL;

        list_for_each_entry(entry, &qp_list->head, list_item) {
                if (vmci_handle_is_equal(entry->handle, handle))
                        return entry;
        }

        return NULL;
}

/*
 * Finds the entry in the list corresponding to a given handle.
 */
static struct qp_guest_endpoint *
qp_guest_handle_to_entry(struct vmci_handle handle)
{
        struct qp_guest_endpoint *entry;
        struct qp_entry *qp = qp_list_find(&qp_guest_endpoints, handle);

        entry = qp ? container_of(
                qp, struct qp_guest_endpoint, qp) : NULL;
        return entry;
}

/*
 * Finds the entry in the list corresponding to a given handle.
 */
static struct qp_broker_entry *
qp_broker_handle_to_entry(struct vmci_handle handle)
{
        struct qp_broker_entry *entry;
        struct qp_entry *qp = qp_list_find(&qp_broker_list, handle);

        entry = qp ? container_of(
                qp, struct qp_broker_entry, qp) : NULL;
        return entry;
}

/*
 * Dispatches a queue pair event message directly into the local event
 * queue.
 */
static int qp_notify_peer_local(bool attach, struct vmci_handle handle)
{
        u32 context_id = vmci_get_context_id();
        struct vmci_event_qp ev;

        memset(&ev, 0, sizeof(ev));
        ev.msg.hdr.dst = vmci_make_handle(context_id, VMCI_EVENT_HANDLER);
        ev.msg.hdr.src = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                          VMCI_CONTEXT_RESOURCE_ID);
        ev.msg.hdr.payload_size = sizeof(ev) - sizeof(ev.msg.hdr);
        ev.msg.event_data.event =
            attach ? VMCI_EVENT_QP_PEER_ATTACH : VMCI_EVENT_QP_PEER_DETACH;
        ev.payload.peer_id = context_id;
        ev.payload.handle = handle;

        return vmci_event_dispatch(&ev.msg.hdr);
}

/*
 * Allocates and initializes a qp_guest_endpoint structure.
 * Allocates a queue_pair rid (and handle) iff the given entry has
 * an invalid handle.  0 through VMCI_RESERVED_RESOURCE_ID_MAX
 * are reserved handles.  Assumes that the QP list mutex is held
 * by the caller.
 */
static struct qp_guest_endpoint *
qp_guest_endpoint_create(struct vmci_handle handle,
                         u32 peer,
                         u32 flags,
                         u64 produce_size,
                         u64 consume_size,
                         void *produce_q,
                         void *consume_q)
{
        int result;
        struct qp_guest_endpoint *entry;
        /* One page each for the queue headers. */
        const u64 num_ppns = DIV_ROUND_UP(produce_size, PAGE_SIZE) +
            DIV_ROUND_UP(consume_size, PAGE_SIZE) + 2;

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

                handle = vmci_make_handle(context_id, VMCI_INVALID_ID);
        }

        entry = kzalloc(sizeof(*entry), GFP_KERNEL);
        if (entry) {
                entry->qp.peer = peer;
                entry->qp.flags = flags;
                entry->qp.produce_size = produce_size;
                entry->qp.consume_size = consume_size;
                entry->qp.ref_count = 0;
                entry->num_ppns = num_ppns;
                entry->produce_q = produce_q;
                entry->consume_q = consume_q;
                INIT_LIST_HEAD(&entry->qp.list_item);

                /* Add resource obj */
                result = vmci_resource_add(&entry->resource,
                                           VMCI_RESOURCE_TYPE_QPAIR_GUEST,
                                           handle);
                entry->qp.handle = vmci_resource_handle(&entry->resource);
                if ((result != VMCI_SUCCESS) ||
                    qp_list_find(&qp_guest_endpoints, entry->qp.handle)) {
                        pr_warn("Failed to add new resource (handle=0x%x:0x%x), error: %d",
                                handle.context, handle.resource, result);
                        kfree(entry);
                        entry = NULL;
                }
        }
        return entry;
}

/*
 * Frees a qp_guest_endpoint structure.
 */
static void qp_guest_endpoint_destroy(struct qp_guest_endpoint *entry)
{
        qp_free_ppn_set(&entry->ppn_set);
        qp_cleanup_queue_mutex(entry->produce_q, entry->consume_q);
        qp_free_queue(entry->produce_q, entry->qp.produce_size);
        qp_free_queue(entry->consume_q, entry->qp.consume_size);
        /* Unlink from resource hash table and free callback */
        vmci_resource_remove(&entry->resource);

        kfree(entry);
}

/*
 * Helper to make a queue_pairAlloc hypercall when the driver is
 * supporting a guest device.
 */
static int qp_alloc_hypercall(const struct qp_guest_endpoint *entry)
{
        struct vmci_qp_alloc_msg *alloc_msg;
        size_t msg_size;
        size_t ppn_size;
        int result;

        if (!entry || entry->num_ppns <= 2)
                return VMCI_ERROR_INVALID_ARGS;

        ppn_size = vmci_use_ppn64() ? sizeof(u64) : sizeof(u32);
        msg_size = sizeof(*alloc_msg) +
            (size_t) entry->num_ppns * ppn_size;
        alloc_msg = kmalloc(msg_size, GFP_KERNEL);
        if (!alloc_msg)
                return VMCI_ERROR_NO_MEM;

        alloc_msg->hdr.dst = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                              VMCI_QUEUEPAIR_ALLOC);
        alloc_msg->hdr.src = VMCI_ANON_SRC_HANDLE;
        alloc_msg->hdr.payload_size = msg_size - VMCI_DG_HEADERSIZE;
        alloc_msg->handle = entry->qp.handle;
        alloc_msg->peer = entry->qp.peer;
        alloc_msg->flags = entry->qp.flags;
        alloc_msg->produce_size = entry->qp.produce_size;
        alloc_msg->consume_size = entry->qp.consume_size;
        alloc_msg->num_ppns = entry->num_ppns;

        result = qp_populate_ppn_set((u8 *)alloc_msg + sizeof(*alloc_msg),
                                     &entry->ppn_set);
        if (result == VMCI_SUCCESS)
                result = vmci_send_datagram(&alloc_msg->hdr);

        kfree(alloc_msg);

        return result;
}

/*
 * Helper to make a queue_pairDetach hypercall when the driver is
 * supporting a guest device.
 */
static int qp_detatch_hypercall(struct vmci_handle handle)
{
        struct vmci_qp_detach_msg detach_msg;

        detach_msg.hdr.dst = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                              VMCI_QUEUEPAIR_DETACH);
        detach_msg.hdr.src = VMCI_ANON_SRC_HANDLE;
        detach_msg.hdr.payload_size = sizeof(handle);
        detach_msg.handle = handle;

        return vmci_send_datagram(&detach_msg.hdr);
}

/*
 * Adds the given entry to the list. Assumes that the list is locked.
 */
static void qp_list_add_entry(struct qp_list *qp_list, struct qp_entry *entry)
{
        if (entry)
                list_add(&entry->list_item, &qp_list->head);
}

/*
 * Removes the given entry from the list. Assumes that the list is locked.
 */
static void qp_list_remove_entry(struct qp_list *qp_list,
                                 struct qp_entry *entry)
{
        if (entry)
                list_del(&entry->list_item);
}

/*
 * Helper for VMCI queue_pair detach interface. Frees the physical
 * pages for the queue pair.
 */
static int qp_detatch_guest_work(struct vmci_handle handle)
{
        int result;
        struct qp_guest_endpoint *entry;
        u32 ref_count = ~0;     /* To avoid compiler warning below */

        mutex_lock(&qp_guest_endpoints.mutex);

        entry = qp_guest_handle_to_entry(handle);
        if (!entry) {
                mutex_unlock(&qp_guest_endpoints.mutex);
                return VMCI_ERROR_NOT_FOUND;
        }

        if (entry->qp.flags & VMCI_QPFLAG_LOCAL) {
                result = VMCI_SUCCESS;

                if (entry->qp.ref_count > 1) {
                        result = qp_notify_peer_local(false, handle);
                        /*
                         * We can fail to notify a local queuepair
                         * because we can't allocate.  We still want
                         * to release the entry if that happens, so
                         * don't bail out yet.
                         */
                }
        } else {
                result = qp_detatch_hypercall(handle);
                if (result < VMCI_SUCCESS) {
                        /*
                         * We failed to notify a non-local queuepair.
                         * That other queuepair might still be
                         * accessing the shared memory, so don't
                         * release the entry yet.  It will get cleaned
                         * up by VMCIqueue_pair_Exit() if necessary
                         * (assuming we are going away, otherwise why
                         * did this fail?).
                         */

                        mutex_unlock(&qp_guest_endpoints.mutex);
                        return result;
                }
        }

        /*
         * If we get here then we either failed to notify a local queuepair, or
         * we succeeded in all cases.  Release the entry if required.
         */

        entry->qp.ref_count--;
        if (entry->qp.ref_count == 0)
                qp_list_remove_entry(&qp_guest_endpoints, &entry->qp);

        /* If we didn't remove the entry, this could change once we unlock. */
        if (entry)
                ref_count = entry->qp.ref_count;

        mutex_unlock(&qp_guest_endpoints.mutex);

        if (ref_count == 0)
                qp_guest_endpoint_destroy(entry);

        return result;
}

/*
 * This functions handles the actual allocation of a VMCI queue
 * pair guest endpoint. Allocates physical pages for the queue
 * pair. It makes OS dependent calls through generic wrappers.
 */
static int qp_alloc_guest_work(struct vmci_handle *handle,
                               struct vmci_queue **produce_q,
                               u64 produce_size,
                               struct vmci_queue **consume_q,
                               u64 consume_size,
                               u32 peer,
                               u32 flags,
                               u32 priv_flags)
{
        const u64 num_produce_pages =
            DIV_ROUND_UP(produce_size, PAGE_SIZE) + 1;
        const u64 num_consume_pages =
            DIV_ROUND_UP(consume_size, PAGE_SIZE) + 1;
        void *my_produce_q = NULL;
        void *my_consume_q = NULL;
        int result;
        struct qp_guest_endpoint *queue_pair_entry = NULL;

        if (priv_flags != VMCI_NO_PRIVILEGE_FLAGS)
                return VMCI_ERROR_NO_ACCESS;

        mutex_lock(&qp_guest_endpoints.mutex);

        queue_pair_entry = qp_guest_handle_to_entry(*handle);
        if (queue_pair_entry) {
                if (queue_pair_entry->qp.flags & VMCI_QPFLAG_LOCAL) {
                        /* Local attach case. */
                        if (queue_pair_entry->qp.ref_count > 1) {
                                pr_devel("Error attempting to attach more than once\n");
                                result = VMCI_ERROR_UNAVAILABLE;
                                goto error_keep_entry;
                        }

                        if (queue_pair_entry->qp.produce_size != consume_size ||
                            queue_pair_entry->qp.consume_size !=
                            produce_size ||
                            queue_pair_entry->qp.flags !=
                            (flags & ~VMCI_QPFLAG_ATTACH_ONLY)) {
                                pr_devel("Error mismatched queue pair in local attach\n");
                                result = VMCI_ERROR_QUEUEPAIR_MISMATCH;
                                goto error_keep_entry;
                        }

                        /*
                         * Do a local attach.  We swap the consume and
                         * produce queues for the attacher and deliver
                         * an attach event.
                         */
                        result = qp_notify_peer_local(true, *handle);
                        if (result < VMCI_SUCCESS)
                                goto error_keep_entry;

                        my_produce_q = queue_pair_entry->consume_q;
                        my_consume_q = queue_pair_entry->produce_q;
                        goto out;
                }

                result = VMCI_ERROR_ALREADY_EXISTS;
                goto error_keep_entry;
        }

        my_produce_q = qp_alloc_queue(produce_size, flags);
        if (!my_produce_q) {
                pr_warn("Error allocating pages for produce queue\n");
                result = VMCI_ERROR_NO_MEM;
                goto error;
        }

        my_consume_q = qp_alloc_queue(consume_size, flags);
        if (!my_consume_q) {
                pr_warn("Error allocating pages for consume queue\n");
                result = VMCI_ERROR_NO_MEM;
                goto error;
        }

        queue_pair_entry = qp_guest_endpoint_create(*handle, peer, flags,
                                                    produce_size, consume_size,
                                                    my_produce_q, my_consume_q);
        if (!queue_pair_entry) {
                pr_warn("Error allocating memory in %s\n", __func__);
                result = VMCI_ERROR_NO_MEM;
                goto error;
        }

        result = qp_alloc_ppn_set(my_produce_q, num_produce_pages, my_consume_q,
                                  num_consume_pages,
                                  &queue_pair_entry->ppn_set);
        if (result < VMCI_SUCCESS) {
                pr_warn("qp_alloc_ppn_set failed\n");
                goto error;
        }

        /*
         * It's only necessary to notify the host if this queue pair will be
         * attached to from another context.
         */
        if (queue_pair_entry->qp.flags & VMCI_QPFLAG_LOCAL) {
                /* Local create case. */
                u32 context_id = vmci_get_context_id();

                /*
                 * Enforce similar checks on local queue pairs as we
                 * do for regular ones.  The handle's context must
                 * match the creator or attacher context id (here they
                 * are both the current context id) and the
                 * attach-only flag cannot exist during create.  We
                 * also ensure specified peer is this context or an
                 * invalid one.
                 */
                if (queue_pair_entry->qp.handle.context != context_id ||
                    (queue_pair_entry->qp.peer != VMCI_INVALID_ID &&
                     queue_pair_entry->qp.peer != context_id)) {
                        result = VMCI_ERROR_NO_ACCESS;
                        goto error;
                }

                if (queue_pair_entry->qp.flags & VMCI_QPFLAG_ATTACH_ONLY) {
                        result = VMCI_ERROR_NOT_FOUND;
                        goto error;
                }
        } else {
                result = qp_alloc_hypercall(queue_pair_entry);
                if (result < VMCI_SUCCESS) {
                        pr_devel("qp_alloc_hypercall result = %d\n", result);
                        goto error;
                }
        }

        qp_init_queue_mutex((struct vmci_queue *)my_produce_q,
                            (struct vmci_queue *)my_consume_q);

        qp_list_add_entry(&qp_guest_endpoints, &queue_pair_entry->qp);

 out:
        queue_pair_entry->qp.ref_count++;
        *handle = queue_pair_entry->qp.handle;
        *produce_q = (struct vmci_queue *)my_produce_q;
        *consume_q = (struct vmci_queue *)my_consume_q;

        /*
         * We should initialize the queue pair header pages on a local
         * queue pair create.  For non-local queue pairs, the
         * hypervisor initializes the header pages in the create step.
         */
        if ((queue_pair_entry->qp.flags & VMCI_QPFLAG_LOCAL) &&
            queue_pair_entry->qp.ref_count == 1) {
                vmci_q_header_init((*produce_q)->q_header, *handle);
                vmci_q_header_init((*consume_q)->q_header, *handle);
        }

        mutex_unlock(&qp_guest_endpoints.mutex);

        return VMCI_SUCCESS;

 error:
        mutex_unlock(&qp_guest_endpoints.mutex);
        if (queue_pair_entry) {
                /* The queues will be freed inside the destroy routine. */
                qp_guest_endpoint_destroy(queue_pair_entry);
        } else {
                qp_free_queue(my_produce_q, produce_size);
                qp_free_queue(my_consume_q, consume_size);
        }
        return result;

 error_keep_entry:
        /* This path should only be used when an existing entry was found. */
        mutex_unlock(&qp_guest_endpoints.mutex);
        return result;
}

/*
 * The first endpoint issuing a queue pair allocation will create the state
 * of the queue pair in the queue pair broker.
 *
 * If the creator is a guest, it will associate a VMX virtual address range
 * with the queue pair as specified by the page_store. For compatibility with
 * older VMX'en, that would use a separate step to set the VMX virtual
 * address range, the virtual address range can be registered later using
 * vmci_qp_broker_set_page_store. In that case, a page_store of NULL should be
 * used.
 *
 * If the creator is the host, a page_store of NULL should be used as well,
 * since the host is not able to supply a page store for the queue pair.
 *
 * For older VMX and host callers, the queue pair will be created in the
 * VMCIQPB_CREATED_NO_MEM state, and for current VMX callers, it will be
 * created in VMCOQPB_CREATED_MEM state.
 */
static int qp_broker_create(struct vmci_handle handle,
                            u32 peer,
                            u32 flags,
                            u32 priv_flags,
                            u64 produce_size,
                            u64 consume_size,
                            struct vmci_qp_page_store *page_store,
                            struct vmci_ctx *context,
                            vmci_event_release_cb wakeup_cb,
                            void *client_data, struct qp_broker_entry **ent)
{
        struct qp_broker_entry *entry = NULL;
        const u32 context_id = vmci_ctx_get_id(context);
        bool is_local = flags & VMCI_QPFLAG_LOCAL;
        int result;
        u64 guest_produce_size;
        u64 guest_consume_size;

        /* Do not create if the caller asked not to. */
        if (flags & VMCI_QPFLAG_ATTACH_ONLY)
                return VMCI_ERROR_NOT_FOUND;

        /*
         * Creator's context ID should match handle's context ID or the creator
         * must allow the context in handle's context ID as the "peer".
         */
        if (handle.context != context_id && handle.context != peer)
                return VMCI_ERROR_NO_ACCESS;

        if (VMCI_CONTEXT_IS_VM(context_id) && VMCI_CONTEXT_IS_VM(peer))
                return VMCI_ERROR_DST_UNREACHABLE;

        /*
         * Creator's context ID for local queue pairs should match the
         * peer, if a peer is specified.
         */
        if (is_local && peer != VMCI_INVALID_ID && context_id != peer)
                return VMCI_ERROR_NO_ACCESS;

        entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
        if (!entry)
                return VMCI_ERROR_NO_MEM;

        if (vmci_ctx_get_id(context) == VMCI_HOST_CONTEXT_ID && !is_local) {
                /*
                 * The queue pair broker entry stores values from the guest
                 * point of view, so a creating host side endpoint should swap
                 * produce and consume values -- unless it is a local queue
                 * pair, in which case no swapping is necessary, since the local
                 * attacher will swap queues.
                 */

                guest_produce_size = consume_size;
                guest_consume_size = produce_size;
        } else {
                guest_produce_size = produce_size;
                guest_consume_size = consume_size;
        }

        entry->qp.handle = handle;
        entry->qp.peer = peer;
        entry->qp.flags = flags;
        entry->qp.produce_size = guest_produce_size;
        entry->qp.consume_size = guest_consume_size;
        entry->qp.ref_count = 1;
        entry->create_id = context_id;
        entry->attach_id = VMCI_INVALID_ID;
        entry->state = VMCIQPB_NEW;
        entry->require_trusted_attach =
            !!(context->priv_flags & VMCI_PRIVILEGE_FLAG_RESTRICTED);
        entry->created_by_trusted =
            !!(priv_flags & VMCI_PRIVILEGE_FLAG_TRUSTED);
        entry->vmci_page_files = false;
        entry->wakeup_cb = wakeup_cb;
        entry->client_data = client_data;
        entry->produce_q = qp_host_alloc_queue(guest_produce_size);
        if (entry->produce_q == NULL) {
                result = VMCI_ERROR_NO_MEM;
                goto error;
        }
        entry->consume_q = qp_host_alloc_queue(guest_consume_size);
        if (entry->consume_q == NULL) {
                result = VMCI_ERROR_NO_MEM;
                goto error;
        }

        qp_init_queue_mutex(entry->produce_q, entry->consume_q);

        INIT_LIST_HEAD(&entry->qp.list_item);

        if (is_local) {
                u8 *tmp;

                entry->local_mem = kcalloc(QPE_NUM_PAGES(entry->qp),
                                           PAGE_SIZE, GFP_KERNEL);
                if (entry->local_mem == NULL) {
                        result = VMCI_ERROR_NO_MEM;
                        goto error;
                }
                entry->state = VMCIQPB_CREATED_MEM;
                entry->produce_q->q_header = entry->local_mem;
                tmp = (u8 *)entry->local_mem + PAGE_SIZE *
                    (DIV_ROUND_UP(entry->qp.produce_size, PAGE_SIZE) + 1);
                entry->consume_q->q_header = (struct vmci_queue_header *)tmp;
        } else if (page_store) {
                /*
                 * The VMX already initialized the queue pair headers, so no
                 * need for the kernel side to do that.
                 */
                result = qp_host_register_user_memory(page_store,
                                                      entry->produce_q,
                                                      entry->consume_q);
                if (result < VMCI_SUCCESS)
                        goto error;

                entry->state = VMCIQPB_CREATED_MEM;
        } else {
                /*
                 * A create without a page_store may be either a host
                 * side create (in which case we are waiting for the
                 * guest side to supply the memory) or an old style
                 * queue pair create (in which case we will expect a
                 * set page store call as the next step).
                 */
                entry->state = VMCIQPB_CREATED_NO_MEM;
        }

        qp_list_add_entry(&qp_broker_list, &entry->qp);
        if (ent != NULL)
                *ent = entry;

        /* Add to resource obj */
        result = vmci_resource_add(&entry->resource,
                                   VMCI_RESOURCE_TYPE_QPAIR_HOST,
                                   handle);
        if (result != VMCI_SUCCESS) {
                pr_warn("Failed to add new resource (handle=0x%x:0x%x), error: %d",
                        handle.context, handle.resource, result);
                goto error;
        }

        entry->qp.handle = vmci_resource_handle(&entry->resource);
        if (is_local) {
                vmci_q_header_init(entry->produce_q->q_header,
                                   entry->qp.handle);
                vmci_q_header_init(entry->consume_q->q_header,
                                   entry->qp.handle);
        }

        vmci_ctx_qp_create(context, entry->qp.handle);

        return VMCI_SUCCESS;

 error:
        if (entry != NULL) {
                qp_host_free_queue(entry->produce_q, guest_produce_size);
                qp_host_free_queue(entry->consume_q, guest_consume_size);
                kfree(entry);
        }

        return result;
}

/*
 * Enqueues an event datagram to notify the peer VM attached to
 * the given queue pair handle about attach/detach event by the
 * given VM.  Returns Payload size of datagram enqueued on
 * success, error code otherwise.
 */
static int qp_notify_peer(bool attach,
                          struct vmci_handle handle,
                          u32 my_id,
                          u32 peer_id)
{
        int rv;
        struct vmci_event_qp ev;

        if (vmci_handle_is_invalid(handle) || my_id == VMCI_INVALID_ID ||
            peer_id == VMCI_INVALID_ID)
                return VMCI_ERROR_INVALID_ARGS;

        /*
         * In vmci_ctx_enqueue_datagram() we enforce the upper limit on
         * number of pending events from the hypervisor to a given VM
         * otherwise a rogue VM could do an arbitrary number of attach
         * and detach operations causing memory pressure in the host
         * kernel.
         */

        memset(&ev, 0, sizeof(ev));
        ev.msg.hdr.dst = vmci_make_handle(peer_id, VMCI_EVENT_HANDLER);
        ev.msg.hdr.src = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
                                          VMCI_CONTEXT_RESOURCE_ID);
        ev.msg.hdr.payload_size = sizeof(ev) - sizeof(ev.msg.hdr);
        ev.msg.event_data.event = attach ?
            VMCI_EVENT_QP_PEER_ATTACH : VMCI_EVENT_QP_PEER_DETACH;
        ev.payload.handle = handle;
        ev.payload.peer_id = my_id;

        rv = vmci_datagram_dispatch(VMCI_HYPERVISOR_CONTEXT_ID,
                                    &ev.msg.hdr, false);
        if (rv < VMCI_SUCCESS)
                pr_warn("Failed to enqueue queue_pair %s event datagram for context (ID=0x%x)\n",
                        attach ? "ATTACH" : "DETACH", peer_id);

        return rv;
}

/*
 * The second endpoint issuing a queue pair allocation will attach to
 * the queue pair registered with the queue pair broker.
 *
 * If the attacher is a guest, it will associate a VMX virtual address
 * range with the queue pair as specified by the page_store. At this
 * point, the already attach host endpoint may start using the queue
 * pair, and an attach event is sent to it. For compatibility with
 * older VMX'en, that used a separate step to set the VMX virtual
 * address range, the virtual address range can be registered later
 * using vmci_qp_broker_set_page_store. In that case, a page_store of
 * NULL should be used, and the attach event will be generated once
 * the actual page store has been set.
 *
 * If the attacher is the host, a page_store of NULL should be used as
 * well, since the page store information is already set by the guest.
 *
 * For new VMX and host callers, the queue pair will be moved to the
 * VMCIQPB_ATTACHED_MEM state, and for older VMX callers, it will be
 * moved to the VMCOQPB_ATTACHED_NO_MEM state.
 */
static int qp_broker_attach(struct qp_broker_entry *entry,
                            u32 peer,
                            u32 flags,
                            u32 priv_flags,
                            u64 produce_size,
                            u64 consume_size,
                            struct vmci_qp_page_store *page_store,
                            struct vmci_ctx *context,
                            vmci_event_release_cb wakeup_cb,
                            void *client_data,
                            struct qp_broker_entry **ent)
{
        const u32 context_id = vmci_ctx_get_id(context);
        bool is_local = flags & VMCI_QPFLAG_LOCAL;
        int result;

        if (entry->state != VMCIQPB_CREATED_NO_MEM &&
            entry->state != VMCIQPB_CREATED_MEM)
                return VMCI_ERROR_UNAVAILABLE;

        if (is_local) {
                if (!(entry->qp.flags & VMCI_QPFLAG_LOCAL) ||
                    context_id != entry->create_id) {
                        return VMCI_ERROR_INVALID_ARGS;
                }
        } else if (context_id == entry->create_id ||
                   context_id == entry->attach_id) {
                return VMCI_ERROR_ALREADY_EXISTS;
        }

        if (VMCI_CONTEXT_IS_VM(context_id) &&
            VMCI_CONTEXT_IS_VM(entry->create_id))
                return VMCI_ERROR_DST_UNREACHABLE;

        /*
         * If we are attaching from a restricted context then the queuepair
         * must have been created by a trusted endpoint.
         */
        if ((context->priv_flags & VMCI_PRIVILEGE_FLAG_RESTRICTED) &&
            !entry->created_by_trusted)
                return VMCI_ERROR_NO_ACCESS;

        /*
         * If we are attaching to a queuepair that was created by a restricted
         * context then we must be trusted.
         */
        if (entry->require_trusted_attach &&
            (!(priv_flags & VMCI_PRIVILEGE_FLAG_TRUSTED)))
                return VMCI_ERROR_NO_ACCESS;

        /*
         * If the creator specifies VMCI_INVALID_ID in "peer" field, access
         * control check is not performed.
         */
        if (entry->qp.peer != VMCI_INVALID_ID && entry->qp.peer != context_id)
                return VMCI_ERROR_NO_ACCESS;

        if (entry->create_id == VMCI_HOST_CONTEXT_ID) {
                /*
                 * Do not attach if the caller doesn't support Host Queue Pairs
                 * and a host created this queue pair.
                 */

                if (!vmci_ctx_supports_host_qp(context))
                        return VMCI_ERROR_INVALID_RESOURCE;

        } else if (context_id == VMCI_HOST_CONTEXT_ID) {
                struct vmci_ctx *create_context;
                bool supports_host_qp;

                /*
                 * Do not attach a host to a user created queue pair if that
                 * user doesn't support host queue pair end points.
                 */

                create_context = vmci_ctx_get(entry->create_id);
                supports_host_qp = vmci_ctx_supports_host_qp(create_context);
                vmci_ctx_put(create_context);

                if (!supports_host_qp)
                        return VMCI_ERROR_INVALID_RESOURCE;
        }

        if ((entry->qp.flags & ~VMCI_QP_ASYMM) != (flags & ~VMCI_QP_ASYMM_PEER))
                return VMCI_ERROR_QUEUEPAIR_MISMATCH;

        if (context_id != VMCI_HOST_CONTEXT_ID) {
                /*
                 * The queue pair broker entry stores values from the guest
                 * point of view, so an attaching guest should match the values
                 * stored in the entry.
                 */

                if (entry->qp.produce_size != produce_size ||
                    entry->qp.consume_size != consume_size) {
                        return VMCI_ERROR_QUEUEPAIR_MISMATCH;
                }
        } else if (entry->qp.produce_size != consume_size ||
                   entry->qp.consume_size != produce_size) {
                return VMCI_ERROR_QUEUEPAIR_MISMATCH;
        }

        if (context_id != VMCI_HOST_CONTEXT_ID) {
                /*
                 * If a guest attached to a queue pair, it will supply
                 * the backing memory.  If this is a pre NOVMVM vmx,
                 * the backing memory will be supplied by calling
                 * vmci_qp_broker_set_page_store() following the
                 * return of the vmci_qp_broker_alloc() call. If it is
                 * a vmx of version NOVMVM or later, the page store
                 * must be supplied as part of the
                 * vmci_qp_broker_alloc call.  Under all circumstances
                 * must the initially created queue pair not have any
                 * memory associated with it already.
                 */

                if (entry->state != VMCIQPB_CREATED_NO_MEM)
                        return VMCI_ERROR_INVALID_ARGS;

                if (page_store != NULL) {
                        /*
                         * Patch up host state to point to guest
                         * supplied memory. The VMX already
                         * initialized the queue pair headers, so no
                         * need for the kernel side to do that.
                         */

                        result = qp_host_register_user_memory(page_store,
                                                              entry->produce_q,
                                                              entry->consume_q);
                        if (result < VMCI_SUCCESS)
                                return result;

                        entry->state = VMCIQPB_ATTACHED_MEM;
                } else {
                        entry->state = VMCIQPB_ATTACHED_NO_MEM;
                }
        } else if (entry->state == VMCIQPB_CREATED_NO_MEM) {
                /*
                 * The host side is attempting to attach to a queue
                 * pair that doesn't have any memory associated with
                 * it. This must be a pre NOVMVM vmx that hasn't set
                 * the page store information yet, or a quiesced VM.
                 */

                return VMCI_ERROR_UNAVAILABLE;
        } else {
                /* The host side has successfully attached to a queue pair. */
                entry->state = VMCIQPB_ATTACHED_MEM;
        }

        if (entry->state == VMCIQPB_ATTACHED_MEM) {
                result =
                    qp_notify_peer(true, entry->qp.handle, context_id,
                                   entry->create_id);
                if (result < VMCI_SUCCESS)
                        pr_warn("Failed to notify peer (ID=0x%x) of attach to queue pair (handle=0x%x:0x%x)\n",
                                entry->create_id, entry->qp.handle.context,
                                entry->qp.handle.resource);
        }

        entry->attach_id = context_id;
        entry->qp.ref_count++;
        if (wakeup_cb) {
                entry->wakeup_cb = wakeup_cb;
                entry->client_data = client_data;
        }

        /*
         * When attaching to local queue pairs, the context already has
         * an entry tracking the queue pair, so don't add another one.
         */
        if (!is_local)
                vmci_ctx_qp_create(context, entry->qp.handle);

        if (ent != NULL)
                *ent = entry;

        return VMCI_SUCCESS;
}

/*
 * queue_pair_Alloc for use when setting up queue pair endpoints
 * on the host.
 */
static int qp_broker_alloc(struct vmci_handle handle,
                           u32 peer,
                           u32 flags,
                           u32 priv_flags,
                           u64 produce_size,
                           u64 consume_size,
                           struct vmci_qp_page_store *page_store,
                           struct vmci_ctx *context,
                           vmci_event_release_cb wakeup_cb,
                           void *client_data,
                           struct qp_broker_entry **ent,
                           bool *swap)
{
        const u32 context_id = vmci_ctx_get_id(context);
        bool create;
        struct qp_broker_entry *entry = NULL;
        bool is_local = flags & VMCI_QPFLAG_LOCAL;
        int result;

        if (vmci_handle_is_invalid(handle) ||
            (flags & ~VMCI_QP_ALL_FLAGS) || is_local ||
            !(produce_size || consume_size) ||
            !context || context_id == VMCI_INVALID_ID ||
            handle.context == VMCI_INVALID_ID) {
                return VMCI_ERROR_INVALID_ARGS;
        }

        if (page_store && !VMCI_QP_PAGESTORE_IS_WELLFORMED(page_store))
                return VMCI_ERROR_INVALID_ARGS;

        /*
         * In the initial argument check, we ensure that non-vmkernel hosts
         * are not allowed to create local queue pairs.
         */

        mutex_lock(&qp_broker_list.mutex);

        if (!is_local && vmci_ctx_qp_exists(context, handle)) {
                pr_devel("Context (ID=0x%x) already attached to queue pair (handle=0x%x:0x%x)\n",
                         context_id, handle.context, handle.resource);
                mutex_unlock(&qp_broker_list.mutex);
                return VMCI_ERROR_ALREADY_EXISTS;
        }

        if (handle.resource != VMCI_INVALID_ID)
                entry = qp_broker_handle_to_entry(handle);

        if (!entry) {
                create = true;
                result =
                    qp_broker_create(handle, peer, flags, priv_flags,
                                     produce_size, consume_size, page_store,
                                     context, wakeup_cb, client_data, ent);
        } else {
                create = false;
                result =
                    qp_broker_attach(entry, peer, flags, priv_flags,
                                     produce_size, consume_size, page_store,
                                     context, wakeup_cb, client_data, ent);
        }

        mutex_unlock(&qp_broker_list.mutex);

        if (swap)
                *swap = (context_id == VMCI_HOST_CONTEXT_ID) &&
                    !(create && is_local);

        return result;
}

/*
 * This function implements the kernel API for allocating a queue
 * pair.
 */
static int qp_alloc_host_work(struct vmci_handle *handle,
                              struct vmci_queue **produce_q,
                              u64 produce_size,
                              struct vmci_queue **consume_q,
                              u64 consume_size,
                              u32 peer,
                              u32 flags,
                              u32 priv_flags,
                              vmci_event_release_cb wakeup_cb,
                              void *client_data)
{
        struct vmci_handle new_handle;
        struct vmci_ctx *context;
        struct qp_broker_entry *entry;
        int result;
        bool swap;

        if (vmci_handle_is_invalid(*handle)) {
                new_handle = vmci_make_handle(
                        VMCI_HOST_CONTEXT_ID, VMCI_INVALID_ID);
        } else
                new_handle = *handle;

        context = vmci_ctx_get(VMCI_HOST_CONTEXT_ID);
        entry = NULL;
        result =
            qp_broker_alloc(new_handle, peer, flags, priv_flags,
                            produce_size, consume_size, NULL, context,
                            wakeup_cb, client_data, &entry, &swap);
        if (result == VMCI_SUCCESS) {
                if (swap) {
                        /*
                         * If this is a local queue pair, the attacher
                         * will swap around produce and consume
                         * queues.
                         */

                        *produce_q = entry->consume_q;
                        *consume_q = entry->produce_q;
                } else {
                        *produce_q = entry->produce_q;
                        *consume_q = entry->consume_q;
                }

                *handle = vmci_resource_handle(&entry->resource);
        } else {
                *handle = VMCI_INVALID_HANDLE;
                pr_devel("queue pair broker failed to alloc (result=%d)\n",
                         result);
        }
        vmci_ctx_put(context);
        return result;
}

/*
 * Allocates a VMCI queue_pair. Only checks validity of input
 * arguments. The real work is done in the host or guest
 * specific function.
 */
int vmci_qp_alloc(struct vmci_handle *handle,
                  struct vmci_queue **produce_q,
                  u64 produce_size,
                  struct vmci_queue **consume_q,
                  u64 consume_size,
                  u32 peer,
                  u32 flags,
                  u32 priv_flags,
                  bool guest_endpoint,
                  vmci_event_release_cb wakeup_cb,
                  void *client_data)
{
        if (!handle || !produce_q || !consume_q ||
            (!produce_size && !consume_size) || (flags & ~VMCI_QP_ALL_FLAGS))
                return VMCI_ERROR_INVALID_ARGS;

        if (guest_endpoint) {
                return qp_alloc_guest_work(handle, produce_q,
                                           produce_size, consume_q,
                                           consume_size, peer,
                                           flags, priv_flags);
        } else {
                return qp_alloc_host_work(handle, produce_q,
                                          produce_size, consume_q,
                                          consume_size, peer, flags,
                                          priv_flags, wakeup_cb, client_data);
        }
}

/*
 * This function implements the host kernel API for detaching from
 * a queue pair.
 */
static int qp_detatch_host_work(struct vmci_handle handle)
{
        int result;
        struct vmci_ctx *context;

        context = vmci_ctx_get(VMCI_HOST_CONTEXT_ID);

        result = vmci_qp_broker_detach(handle, context);

        vmci_ctx_put(context);
        return result;
}

/*
 * Detaches from a VMCI queue_pair. Only checks validity of input argument.
 * Real work is done in the host or guest specific function.
 */
static int qp_detatch(struct vmci_handle handle, bool guest_endpoint)
{
        if (vmci_handle_is_invalid(handle))
                return VMCI_ERROR_INVALID_ARGS;

        if (guest_endpoint)
                return qp_detatch_guest_work(handle);
        else
                return qp_detatch_host_work(handle);
}

/*
 * Returns the entry from the head of the list. Assumes that the list is
 * locked.
 */
static struct qp_entry *qp_list_get_head(struct qp_list *qp_list)
{
        if (!list_empty(&qp_list->head)) {
                struct qp_entry *entry =
                    list_first_entry(&qp_list->head, struct qp_entry,
                                     list_item);
                return entry;
        }

        return NULL;
}

void vmci_qp_broker_exit(void)
{
        struct qp_entry *entry;
        struct qp_broker_entry *be;

        mutex_lock(&qp_broker_list.mutex);

        while ((entry = qp_list_get_head(&qp_broker_list))) {
                be = (struct qp_broker_entry *)entry;

                qp_list_remove_entry(&qp_broker_list, entry);
                kfree(be);
        }

        mutex_unlock(&qp_broker_list.mutex);
}

/*
 * Requests that a queue pair be allocated with the VMCI queue
 * pair broker. Allocates a queue pair entry if one does not
 * exist. Attaches to one if it exists, and retrieves the page
 * files backing that queue_pair.  Assumes that the queue pair
 * broker lock is held.
 */
int vmci_qp_broker_alloc(struct vmci_handle handle,
                         u32 peer,
                         u32 flags,
                         u32 priv_flags,
                         u64 produce_size,
                         u64 consume_size,
                         struct vmci_qp_page_store *page_store,
                         struct vmci_ctx *context)
{
        if (!QP_SIZES_ARE_VALID(produce_size, consume_size))
                return VMCI_ERROR_NO_RESOURCES;

        return qp_broker_alloc(handle, peer, flags, priv_flags,
                               produce_size, consume_size,
                               page_store, context, NULL, NULL, NULL, NULL);
}

/*
 * VMX'en with versions lower than VMCI_VERSION_NOVMVM use a separate
 * step to add the UVAs of the VMX mapping of the queue pair. This function
 * provides backwards compatibility with such VMX'en, and takes care of
 * registering the page store for a queue pair previously allocated by the
 * VMX during create or attach. This function will move the queue pair state
 * to either from VMCIQBP_CREATED_NO_MEM to VMCIQBP_CREATED_MEM or
 * VMCIQBP_ATTACHED_NO_MEM to VMCIQBP_ATTACHED_MEM. If moving to the
 * attached state with memory, the queue pair is ready to be used by the
 * host peer, and an attached event will be generated.
 *
 * Assumes that the queue pair broker lock is held.
 *
 * This function is only used by the hosted platform, since there is no
 * issue with backwards compatibility for vmkernel.
 */
int vmci_qp_broker_set_page_store(struct vmci_handle handle,
                                  u64 produce_uva,
                                  u64 consume_uva,
                                  struct vmci_ctx *context)
{
        struct qp_broker_entry *entry;
        int result;
        const u32 context_id = vmci_ctx_get_id(context);

        if (vmci_handle_is_invalid(handle) || !context ||
            context_id == VMCI_INVALID_ID)
                return VMCI_ERROR_INVALID_ARGS;

        /*
         * We only support guest to host queue pairs, so the VMX must
         * supply UVAs for the mapped page files.
         */

        if (produce_uva == 0 || consume_uva == 0)
                return VMCI_ERROR_INVALID_ARGS;

        mutex_lock(&qp_broker_list.mutex);

        if (!vmci_ctx_qp_exists(context, handle)) {
                pr_warn("Context (ID=0x%x) not attached to queue pair (handle=0x%x:0x%x)\n",
                        context_id, handle.context, handle.resource);
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        entry = qp_broker_handle_to_entry(handle);
        if (!entry) {
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        /*
         * If I'm the owner then I can set the page store.
         *
         * Or, if a host created the queue_pair and I'm the attached peer
         * then I can set the page store.
         */
        if (entry->create_id != context_id &&
            (entry->create_id != VMCI_HOST_CONTEXT_ID ||
             entry->attach_id != context_id)) {
                result = VMCI_ERROR_QUEUEPAIR_NOTOWNER;
                goto out;
        }

        if (entry->state != VMCIQPB_CREATED_NO_MEM &&
            entry->state != VMCIQPB_ATTACHED_NO_MEM) {
                result = VMCI_ERROR_UNAVAILABLE;
                goto out;
        }

        result = qp_host_get_user_memory(produce_uva, consume_uva,
                                         entry->produce_q, entry->consume_q);
        if (result < VMCI_SUCCESS)
                goto out;

        result = qp_host_map_queues(entry->produce_q, entry->consume_q);
        if (result < VMCI_SUCCESS) {
                qp_host_unregister_user_memory(entry->produce_q,
                                               entry->consume_q);
                goto out;
        }

        if (entry->state == VMCIQPB_CREATED_NO_MEM)
                entry->state = VMCIQPB_CREATED_MEM;
        else
                entry->state = VMCIQPB_ATTACHED_MEM;

        entry->vmci_page_files = true;

        if (entry->state == VMCIQPB_ATTACHED_MEM) {
                result =
                    qp_notify_peer(true, handle, context_id, entry->create_id);
                if (result < VMCI_SUCCESS) {
                        pr_warn("Failed to notify peer (ID=0x%x) of attach to queue pair (handle=0x%x:0x%x)\n",
                                entry->create_id, entry->qp.handle.context,
                                entry->qp.handle.resource);
                }
        }

        result = VMCI_SUCCESS;
 out:
        mutex_unlock(&qp_broker_list.mutex);
        return result;
}

/*
 * Resets saved queue headers for the given QP broker
 * entry. Should be used when guest memory becomes available
 * again, or the guest detaches.
 */
static void qp_reset_saved_headers(struct qp_broker_entry *entry)
{
        entry->produce_q->saved_header = NULL;
        entry->consume_q->saved_header = NULL;
}

/*
 * The main entry point for detaching from a queue pair registered with the
 * queue pair broker. If more than one endpoint is attached to the queue
 * pair, the first endpoint will mainly decrement a reference count and
 * generate a notification to its peer. The last endpoint will clean up
 * the queue pair state registered with the broker.
 *
 * When a guest endpoint detaches, it will unmap and unregister the guest
 * memory backing the queue pair. If the host is still attached, it will
 * no longer be able to access the queue pair content.
 *
 * If the queue pair is already in a state where there is no memory
 * registered for the queue pair (any *_NO_MEM state), it will transition to
 * the VMCIQPB_SHUTDOWN_NO_MEM state. This will also happen, if a guest
 * endpoint is the first of two endpoints to detach. If the host endpoint is
 * the first out of two to detach, the queue pair will move to the
 * VMCIQPB_SHUTDOWN_MEM state.
 */
int vmci_qp_broker_detach(struct vmci_handle handle, struct vmci_ctx *context)
{
        struct qp_broker_entry *entry;
        const u32 context_id = vmci_ctx_get_id(context);
        u32 peer_id;
        bool is_local = false;
        int result;

        if (vmci_handle_is_invalid(handle) || !context ||
            context_id == VMCI_INVALID_ID) {
                return VMCI_ERROR_INVALID_ARGS;
        }

        mutex_lock(&qp_broker_list.mutex);

        if (!vmci_ctx_qp_exists(context, handle)) {
                pr_devel("Context (ID=0x%x) not attached to queue pair (handle=0x%x:0x%x)\n",
                         context_id, handle.context, handle.resource);
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        entry = qp_broker_handle_to_entry(handle);
        if (!entry) {
                pr_devel("Context (ID=0x%x) reports being attached to queue pair(handle=0x%x:0x%x) that isn't present in broker\n",
                         context_id, handle.context, handle.resource);
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        if (context_id != entry->create_id && context_id != entry->attach_id) {
                result = VMCI_ERROR_QUEUEPAIR_NOTATTACHED;
                goto out;
        }

        if (context_id == entry->create_id) {
                peer_id = entry->attach_id;
                entry->create_id = VMCI_INVALID_ID;
        } else {
                peer_id = entry->create_id;
                entry->attach_id = VMCI_INVALID_ID;
        }
        entry->qp.ref_count--;

        is_local = entry->qp.flags & VMCI_QPFLAG_LOCAL;

        if (context_id != VMCI_HOST_CONTEXT_ID) {
                bool headers_mapped;

                /*
                 * Pre NOVMVM vmx'en may detach from a queue pair
                 * before setting the page store, and in that case
                 * there is no user memory to detach from. Also, more
                 * recent VMX'en may detach from a queue pair in the
                 * quiesced state.
                 */

                qp_acquire_queue_mutex(entry->produce_q);
                headers_mapped = entry->produce_q->q_header ||
                    entry->consume_q->q_header;
                if (QPBROKERSTATE_HAS_MEM(entry)) {
                        result =
                            qp_host_unmap_queues(INVALID_VMCI_GUEST_MEM_ID,
                                                 entry->produce_q,
                                                 entry->consume_q);
                        if (result < VMCI_SUCCESS)
                                pr_warn("Failed to unmap queue headers for queue pair (handle=0x%x:0x%x,result=%d)\n",
                                        handle.context, handle.resource,
                                        result);

                        qp_host_unregister_user_memory(entry->produce_q,
                                                       entry->consume_q);

                }

                if (!headers_mapped)
                        qp_reset_saved_headers(entry);

                qp_release_queue_mutex(entry->produce_q);

                if (!headers_mapped && entry->wakeup_cb)
                        entry->wakeup_cb(entry->client_data);

        } else {
                if (entry->wakeup_cb) {
                        entry->wakeup_cb = NULL;
                        entry->client_data = NULL;
                }
        }

        if (entry->qp.ref_count == 0) {
                qp_list_remove_entry(&qp_broker_list, &entry->qp);

                if (is_local)
                        kfree(entry->local_mem);

                qp_cleanup_queue_mutex(entry->produce_q, entry->consume_q);
                qp_host_free_queue(entry->produce_q, entry->qp.produce_size);
                qp_host_free_queue(entry->consume_q, entry->qp.consume_size);
                /* Unlink from resource hash table and free callback */
                vmci_resource_remove(&entry->resource);

                kfree(entry);

                vmci_ctx_qp_destroy(context, handle);
        } else {
                qp_notify_peer(false, handle, context_id, peer_id);
                if (context_id == VMCI_HOST_CONTEXT_ID &&
                    QPBROKERSTATE_HAS_MEM(entry)) {
                        entry->state = VMCIQPB_SHUTDOWN_MEM;
                } else {
                        entry->state = VMCIQPB_SHUTDOWN_NO_MEM;
                }

                if (!is_local)
                        vmci_ctx_qp_destroy(context, handle);

        }
        result = VMCI_SUCCESS;
 out:
        mutex_unlock(&qp_broker_list.mutex);
        return result;
}

/*
 * Establishes the necessary mappings for a queue pair given a
 * reference to the queue pair guest memory. This is usually
 * called when a guest is unquiesced and the VMX is allowed to
 * map guest memory once again.
 */
int vmci_qp_broker_map(struct vmci_handle handle,
                       struct vmci_ctx *context,
                       u64 guest_mem)
{
        struct qp_broker_entry *entry;
        const u32 context_id = vmci_ctx_get_id(context);
        int result;

        if (vmci_handle_is_invalid(handle) || !context ||
            context_id == VMCI_INVALID_ID)
                return VMCI_ERROR_INVALID_ARGS;

        mutex_lock(&qp_broker_list.mutex);

        if (!vmci_ctx_qp_exists(context, handle)) {
                pr_devel("Context (ID=0x%x) not attached to queue pair (handle=0x%x:0x%x)\n",
                         context_id, handle.context, handle.resource);
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        entry = qp_broker_handle_to_entry(handle);
        if (!entry) {
                pr_devel("Context (ID=0x%x) reports being attached to queue pair (handle=0x%x:0x%x) that isn't present in broker\n",
                         context_id, handle.context, handle.resource);
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        if (context_id != entry->create_id && context_id != entry->attach_id) {
                result = VMCI_ERROR_QUEUEPAIR_NOTATTACHED;
                goto out;
        }

        result = VMCI_SUCCESS;

        if (context_id != VMCI_HOST_CONTEXT_ID &&
            !QPBROKERSTATE_HAS_MEM(entry)) {
                struct vmci_qp_page_store page_store;

                page_store.pages = guest_mem;
                page_store.len = QPE_NUM_PAGES(entry->qp);

                qp_acquire_queue_mutex(entry->produce_q);
                qp_reset_saved_headers(entry);
                result =
                    qp_host_register_user_memory(&page_store,
                                                 entry->produce_q,
                                                 entry->consume_q);
                qp_release_queue_mutex(entry->produce_q);
                if (result == VMCI_SUCCESS) {
                        /* Move state from *_NO_MEM to *_MEM */

                        entry->state++;

                        if (entry->wakeup_cb)
                                entry->wakeup_cb(entry->client_data);
                }
        }

 out:
        mutex_unlock(&qp_broker_list.mutex);
        return result;
}

/*
 * Saves a snapshot of the queue headers for the given QP broker
 * entry. Should be used when guest memory is unmapped.
 * Results:
 * VMCI_SUCCESS on success, appropriate error code if guest memory
 * can't be accessed..
 */
static int qp_save_headers(struct qp_broker_entry *entry)
{
        int result;

        if (entry->produce_q->saved_header != NULL &&
            entry->consume_q->saved_header != NULL) {
                /*
                 *  If the headers have already been saved, we don't need to do
                 *  it again, and we don't want to map in the headers
                 *  unnecessarily.
                 */

                return VMCI_SUCCESS;
        }

        if (NULL == entry->produce_q->q_header ||
            NULL == entry->consume_q->q_header) {
                result = qp_host_map_queues(entry->produce_q, entry->consume_q);
                if (result < VMCI_SUCCESS)
                        return result;
        }

        memcpy(&entry->saved_produce_q, entry->produce_q->q_header,
               sizeof(entry->saved_produce_q));
        entry->produce_q->saved_header = &entry->saved_produce_q;
        memcpy(&entry->saved_consume_q, entry->consume_q->q_header,
               sizeof(entry->saved_consume_q));
        entry->consume_q->saved_header = &entry->saved_consume_q;

        return VMCI_SUCCESS;
}

/*
 * Removes all references to the guest memory of a given queue pair, and
 * will move the queue pair from state *_MEM to *_NO_MEM. It is usually
 * called when a VM is being quiesced where access to guest memory should
 * avoided.
 */
int vmci_qp_broker_unmap(struct vmci_handle handle,
                         struct vmci_ctx *context,
                         u32 gid)
{
        struct qp_broker_entry *entry;
        const u32 context_id = vmci_ctx_get_id(context);
        int result;

        if (vmci_handle_is_invalid(handle) || !context ||
            context_id == VMCI_INVALID_ID)
                return VMCI_ERROR_INVALID_ARGS;

        mutex_lock(&qp_broker_list.mutex);

        if (!vmci_ctx_qp_exists(context, handle)) {
                pr_devel("Context (ID=0x%x) not attached to queue pair (handle=0x%x:0x%x)\n",
                         context_id, handle.context, handle.resource);
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        entry = qp_broker_handle_to_entry(handle);
        if (!entry) {
                pr_devel("Context (ID=0x%x) reports being attached to queue pair (handle=0x%x:0x%x) that isn't present in broker\n",
                         context_id, handle.context, handle.resource);
                result = VMCI_ERROR_NOT_FOUND;
                goto out;
        }

        if (context_id != entry->create_id && context_id != entry->attach_id) {
                result = VMCI_ERROR_QUEUEPAIR_NOTATTACHED;
                goto out;
        }

        if (context_id != VMCI_HOST_CONTEXT_ID &&
            QPBROKERSTATE_HAS_MEM(entry)) {
                qp_acquire_queue_mutex(entry->produce_q);
                result = qp_save_headers(entry);
                if (result < VMCI_SUCCESS)
                        pr_warn("Failed to save queue headers for queue pair (handle=0x%x:0x%x,result=%d)\n",
                                handle.context, handle.resource, result);

                qp_host_unmap_queues(gid, entry->produce_q, entry->consume_q);

                /*
                 * On hosted, when we unmap queue pairs, the VMX will also
                 * unmap the guest memory, so we invalidate the previously
                 * registered memory. If the queue pair is mapped again at a
                 * later point in time, we will need to reregister the user
                 * memory with a possibly new user VA.
                 */
                qp_host_unregister_user_memory(entry->produce_q,
                                               entry->consume_q);

                /*
                 * Move state from *_MEM to *_NO_MEM.
                 */
                entry->state--;

                qp_release_queue_mutex(entry->produce_q);
        }

        result = VMCI_SUCCESS;

 out:
        mutex_unlock(&qp_broker_list.mutex);
        return result;
}

/*
 * Destroys all guest queue pair endpoints. If active guest queue
 * pairs still exist, hypercalls to attempt detach from these
 * queue pairs will be made. Any failure to detach is silently
 * ignored.
 */
void vmci_qp_guest_endpoints_exit(void)
{
        struct qp_entry *entry;
        struct qp_guest_endpoint *ep;

        mutex_lock(&qp_guest_endpoints.mutex);

        while ((entry = qp_list_get_head(&qp_guest_endpoints))) {
                ep = (struct qp_guest_endpoint *)entry;

                /* Don't make a hypercall for local queue_pairs. */
                if (!(entry->flags & VMCI_QPFLAG_LOCAL))
                        qp_detatch_hypercall(entry->handle);

                /* We cannot fail the exit, so let's reset ref_count. */
                entry->ref_count = 0;
                qp_list_remove_entry(&qp_guest_endpoints, entry);

                qp_guest_endpoint_destroy(ep);
        }

        mutex_unlock(&qp_guest_endpoints.mutex);
}

/*
 * Helper routine that will lock the queue pair before subsequent
 * operations.
 * Note: Non-blocking on the host side is currently only implemented in ESX.
 * Since non-blocking isn't yet implemented on the host personality we
 * have no reason to acquire a spin lock.  So to avoid the use of an
 * unnecessary lock only acquire the mutex if we can block.
 */
static void qp_lock(const struct vmci_qp *qpair)
{
        qp_acquire_queue_mutex(qpair->produce_q);
}

/*
 * Helper routine that unlocks the queue pair after calling
 * qp_lock.
 */
static void qp_unlock(const struct vmci_qp *qpair)
{
        qp_release_queue_mutex(qpair->produce_q);
}

/*
 * The queue headers may not be mapped at all times. If a queue is
 * currently not mapped, it will be attempted to do so.
 */
static int qp_map_queue_headers(struct vmci_queue *produce_q,
                                struct vmci_queue *consume_q)
{
        int result;

        if (NULL == produce_q->q_header || NULL == consume_q->q_header) {
                result = qp_host_map_queues(produce_q, consume_q);
                if (result < VMCI_SUCCESS)
                        return (produce_q->saved_header &&
                                consume_q->saved_header) ?
                            VMCI_ERROR_QUEUEPAIR_NOT_READY :
                            VMCI_ERROR_QUEUEPAIR_NOTATTACHED;
        }

        return VMCI_SUCCESS;
}

/*
 * Helper routine that will retrieve the produce and consume
 * headers of a given queue pair. If the guest memory of the
 * queue pair is currently not available, the saved queue headers
 * will be returned, if these are available.
 */
static int qp_get_queue_headers(const struct vmci_qp *qpair,
                                struct vmci_queue_header **produce_q_header,
                                struct vmci_queue_header **consume_q_header)
{
        int result;

        result = qp_map_queue_headers(qpair->produce_q, qpair->consume_q);
        if (result == VMCI_SUCCESS) {
                *produce_q_header = qpair->produce_q->q_header;
                *consume_q_header = qpair->consume_q->q_header;
        } else if (qpair->produce_q->saved_header &&
                   qpair->consume_q->saved_header) {
                *produce_q_header = qpair->produce_q->saved_header;
                *consume_q_header = qpair->consume_q->saved_header;
                result = VMCI_SUCCESS;
        }

        return result;
}

/*
 * Callback from VMCI queue pair broker indicating that a queue
 * pair that was previously not ready, now either is ready or
 * gone forever.
 */
static int qp_wakeup_cb(void *client_data)
{
        struct vmci_qp *qpair = (struct vmci_qp *)client_data;

        qp_lock(qpair);
        while (qpair->blocked > 0) {
                qpair->blocked--;
                qpair->generation++;
                wake_up(&qpair->event);
        }
        qp_unlock(qpair);

        return VMCI_SUCCESS;
}

/*
 * Makes the calling thread wait for the queue pair to become
 * ready for host side access.  Returns true when thread is
 * woken up after queue pair state change, false otherwise.
 */
static bool qp_wait_for_ready_queue(struct vmci_qp *qpair)
{
        unsigned int generation;

        qpair->blocked++;
        generation = qpair->generation;
        qp_unlock(qpair);
        wait_event(qpair->event, generation != qpair->generation);
        qp_lock(qpair);

        return true;
}

/*
 * Enqueues a given buffer to the produce queue using the provided
 * function. As many bytes as possible (space available in the queue)
 * are enqueued.  Assumes the queue->mutex has been acquired.  Returns
 * VMCI_ERROR_QUEUEPAIR_NOSPACE if no space was available to enqueue
 * data, VMCI_ERROR_INVALID_SIZE, if any queue pointer is outside the
 * queue (as defined by the queue size), VMCI_ERROR_INVALID_ARGS, if
 * an error occured when accessing the buffer,
 * VMCI_ERROR_QUEUEPAIR_NOTATTACHED, if the queue pair pages aren't
 * available.  Otherwise, the number of bytes written to the queue is
 * returned.  Updates the tail pointer of the produce queue.
 */
static ssize_t qp_enqueue_locked(struct vmci_queue *produce_q,
                                 struct vmci_queue *consume_q,
                                 const u64 produce_q_size,
                                 struct iov_iter *from)
{
        s64 free_space;
        u64 tail;
        size_t buf_size = iov_iter_count(from);
        size_t written;
        ssize_t result;

        result = qp_map_queue_headers(produce_q, consume_q);
        if (unlikely(result != VMCI_SUCCESS))
                return result;

        free_space = vmci_q_header_free_space(produce_q->q_header,
                                              consume_q->q_header,
                                              produce_q_size);
        if (free_space == 0)
                return VMCI_ERROR_QUEUEPAIR_NOSPACE;

        if (free_space < VMCI_SUCCESS)
                return (ssize_t) free_space;

        written = (size_t) (free_space > buf_size ? buf_size : free_space);
        tail = vmci_q_header_producer_tail(produce_q->q_header);
        if (likely(tail + written < produce_q_size)) {
                result = qp_memcpy_to_queue_iter(produce_q, tail, from, written);
        } else {
                /* Tail pointer wraps around. */

                const size_t tmp = (size_t) (produce_q_size - tail);

                result = qp_memcpy_to_queue_iter(produce_q, tail, from, tmp);
                if (result >= VMCI_SUCCESS)
                        result = qp_memcpy_to_queue_iter(produce_q, 0, from,
                                                 written - tmp);
        }

        if (result < VMCI_SUCCESS)
                return result;

        /*
         * This virt_wmb() ensures that data written to the queue
         * is observable before the new producer_tail is.
         */
        virt_wmb();

        vmci_q_header_add_producer_tail(produce_q->q_header, written,
                                        produce_q_size);
        return written;
}

/*
 * Dequeues data (if available) from the given consume queue. Writes data
 * to the user provided buffer using the provided function.
 * Assumes the queue->mutex has been acquired.
 * Results:
 * VMCI_ERROR_QUEUEPAIR_NODATA if no data was available to dequeue.
 * VMCI_ERROR_INVALID_SIZE, if any queue pointer is outside the queue
 * (as defined by the queue size).
 * VMCI_ERROR_INVALID_ARGS, if an error occured when accessing the buffer.
 * Otherwise the number of bytes dequeued is returned.
 * Side effects:
 * Updates the head pointer of the consume queue.
 */
static ssize_t qp_dequeue_locked(struct vmci_queue *produce_q,
                                 struct vmci_queue *consume_q,
                                 const u64 consume_q_size,
                                 struct iov_iter *to,
                                 bool update_consumer)
{
        size_t buf_size = iov_iter_count(to);
        s64 buf_ready;
        u64 head;
        size_t read;
        ssize_t result;

        result = qp_map_queue_headers(produce_q, consume_q);
        if (unlikely(result != VMCI_SUCCESS))
                return result;

        buf_ready = vmci_q_header_buf_ready(consume_q->q_header,
                                            produce_q->q_header,
                                            consume_q_size);
        if (buf_ready == 0)
                return VMCI_ERROR_QUEUEPAIR_NODATA;

        if (buf_ready < VMCI_SUCCESS)
                return (ssize_t) buf_ready;

        /*
         * This virt_rmb() ensures that data from the queue will be read
         * after we have determined how much is ready to be consumed.
         */
        virt_rmb();

        read = (size_t) (buf_ready > buf_size ? buf_size : buf_ready);
        head = vmci_q_header_consumer_head(produce_q->q_header);
        if (likely(head + read < consume_q_size)) {
                result = qp_memcpy_from_queue_iter(to, consume_q, head, read);
        } else {
                /* Head pointer wraps around. */

                const size_t tmp = (size_t) (consume_q_size - head);

                result = qp_memcpy_from_queue_iter(to, consume_q, head, tmp);
                if (result >= VMCI_SUCCESS)
                        result = qp_memcpy_from_queue_iter(to, consume_q, 0,
                                                   read - tmp);

        }

        if (result < VMCI_SUCCESS)
                return result;

        if (update_consumer)
                vmci_q_header_add_consumer_head(produce_q->q_header,
                                                read, consume_q_size);

        return read;
}

/*
 * vmci_qpair_alloc() - Allocates a queue pair.
 * @qpair:      Pointer for the new vmci_qp struct.
 * @handle:     Handle to track the resource.
 * @produce_qsize:      Desired size of the producer queue.
 * @consume_qsize:      Desired size of the consumer queue.
 * @peer:       ContextID of the peer.
 * @flags:      VMCI flags.
 * @priv_flags: VMCI priviledge flags.
 *
 * This is the client interface for allocating the memory for a
 * vmci_qp structure and then attaching to the underlying
 * queue.  If an error occurs allocating the memory for the
 * vmci_qp structure no attempt is made to attach.  If an
 * error occurs attaching, then the structure is freed.
 */
int vmci_qpair_alloc(struct vmci_qp **qpair,
                     struct vmci_handle *handle,
                     u64 produce_qsize,
                     u64 consume_qsize,
                     u32 peer,
                     u32 flags,
                     u32 priv_flags)
{
        struct vmci_qp *my_qpair;
        int retval;
        struct vmci_handle src = VMCI_INVALID_HANDLE;
        struct vmci_handle dst = vmci_make_handle(peer, VMCI_INVALID_ID);
        enum vmci_route route;
        vmci_event_release_cb wakeup_cb;
        void *client_data;

        /*
         * Restrict the size of a queuepair.  The device already
         * enforces a limit on the total amount of memory that can be
         * allocated to queuepairs for a guest.  However, we try to
         * allocate this memory before we make the queuepair
         * allocation hypercall.  On Linux, we allocate each page
         * separately, which means rather than fail, the guest will
         * thrash while it tries to allocate, and will become
         * increasingly unresponsive to the point where it appears to
         * be hung.  So we place a limit on the size of an individual
         * queuepair here, and leave the device to enforce the
         * restriction on total queuepair memory.  (Note that this
         * doesn't prevent all cases; a user with only this much
         * physical memory could still get into trouble.)  The error
         * used by the device is NO_RESOURCES, so use that here too.
         */

        if (!QP_SIZES_ARE_VALID(produce_qsize, consume_qsize))
                return VMCI_ERROR_NO_RESOURCES;

        retval = vmci_route(&src, &dst, false, &route);
        if (retval < VMCI_SUCCESS)
                route = vmci_guest_code_active() ?
                    VMCI_ROUTE_AS_GUEST : VMCI_ROUTE_AS_HOST;

        if (flags & (VMCI_QPFLAG_NONBLOCK | VMCI_QPFLAG_PINNED)) {
                pr_devel("NONBLOCK OR PINNED set");
                return VMCI_ERROR_INVALID_ARGS;
        }

        my_qpair = kzalloc(sizeof(*my_qpair), GFP_KERNEL);
        if (!my_qpair)
                return VMCI_ERROR_NO_MEM;

        my_qpair->produce_q_size = produce_qsize;
        my_qpair->consume_q_size = consume_qsize;
        my_qpair->peer = peer;
        my_qpair->flags = flags;
        my_qpair->priv_flags = priv_flags;

        wakeup_cb = NULL;
        client_data = NULL;

        if (VMCI_ROUTE_AS_HOST == route) {
                my_qpair->guest_endpoint = false;
                if (!(flags & VMCI_QPFLAG_LOCAL)) {
                        my_qpair->blocked = 0;
                        my_qpair->generation = 0;
                        init_waitqueue_head(&my_qpair->event);
                        wakeup_cb = qp_wakeup_cb;
                        client_data = (void *)my_qpair;
                }
        } else {
                my_qpair->guest_endpoint = true;
        }

        retval = vmci_qp_alloc(handle,
                               &my_qpair->produce_q,
                               my_qpair->produce_q_size,
                               &my_qpair->consume_q,
                               my_qpair->consume_q_size,
                               my_qpair->peer,
                               my_qpair->flags,
                               my_qpair->priv_flags,
                               my_qpair->guest_endpoint,
                               wakeup_cb, client_data);

        if (retval < VMCI_SUCCESS) {
                kfree(my_qpair);
                return retval;
        }

        *qpair = my_qpair;
        my_qpair->handle = *handle;

        return retval;
}
EXPORT_SYMBOL_GPL(vmci_qpair_alloc);

/*
 * vmci_qpair_detach() - Detatches the client from a queue pair.
 * @qpair:      Reference of a pointer to the qpair struct.
 *
 * This is the client interface for detaching from a VMCIQPair.
 * Note that this routine will free the memory allocated for the
 * vmci_qp structure too.
 */
int vmci_qpair_detach(struct vmci_qp **qpair)
{
        int result;
        struct vmci_qp *old_qpair;

        if (!qpair || !(*qpair))
                return VMCI_ERROR_INVALID_ARGS;

        old_qpair = *qpair;
        result = qp_detatch(old_qpair->handle, old_qpair->guest_endpoint);

        /*
         * The guest can fail to detach for a number of reasons, and
         * if it does so, it will cleanup the entry (if there is one).
         * The host can fail too, but it won't cleanup the entry
         * immediately, it will do that later when the context is
         * freed.  Either way, we need to release the qpair struct
         * here; there isn't much the caller can do, and we don't want
         * to leak.
         */

        memset(old_qpair, 0, sizeof(*old_qpair));
        old_qpair->handle = VMCI_INVALID_HANDLE;
        old_qpair->peer = VMCI_INVALID_ID;
        kfree(old_qpair);
        *qpair = NULL;

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_detach);

/*
 * vmci_qpair_get_produce_indexes() - Retrieves the indexes of the producer.
 * @qpair:      Pointer to the queue pair struct.
 * @producer_tail:      Reference used for storing producer tail index.
 * @consumer_head:      Reference used for storing the consumer head index.
 *
 * This is the client interface for getting the current indexes of the
 * QPair from the point of the view of the caller as the producer.
 */
int vmci_qpair_get_produce_indexes(const struct vmci_qp *qpair,
                                   u64 *producer_tail,
                                   u64 *consumer_head)
{
        struct vmci_queue_header *produce_q_header;
        struct vmci_queue_header *consume_q_header;
        int result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);
        result =
            qp_get_queue_headers(qpair, &produce_q_header, &consume_q_header);
        if (result == VMCI_SUCCESS)
                vmci_q_header_get_pointers(produce_q_header, consume_q_header,
                                           producer_tail, consumer_head);
        qp_unlock(qpair);

        if (result == VMCI_SUCCESS &&
            ((producer_tail && *producer_tail >= qpair->produce_q_size) ||
             (consumer_head && *consumer_head >= qpair->produce_q_size)))
                return VMCI_ERROR_INVALID_SIZE;

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_get_produce_indexes);

/*
 * vmci_qpair_get_consume_indexes() - Retrieves the indexes of the consumer.
 * @qpair:      Pointer to the queue pair struct.
 * @consumer_tail:      Reference used for storing consumer tail index.
 * @producer_head:      Reference used for storing the producer head index.
 *
 * This is the client interface for getting the current indexes of the
 * QPair from the point of the view of the caller as the consumer.
 */
int vmci_qpair_get_consume_indexes(const struct vmci_qp *qpair,
                                   u64 *consumer_tail,
                                   u64 *producer_head)
{
        struct vmci_queue_header *produce_q_header;
        struct vmci_queue_header *consume_q_header;
        int result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);
        result =
            qp_get_queue_headers(qpair, &produce_q_header, &consume_q_header);
        if (result == VMCI_SUCCESS)
                vmci_q_header_get_pointers(consume_q_header, produce_q_header,
                                           consumer_tail, producer_head);
        qp_unlock(qpair);

        if (result == VMCI_SUCCESS &&
            ((consumer_tail && *consumer_tail >= qpair->consume_q_size) ||
             (producer_head && *producer_head >= qpair->consume_q_size)))
                return VMCI_ERROR_INVALID_SIZE;

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_get_consume_indexes);

/*
 * vmci_qpair_produce_free_space() - Retrieves free space in producer queue.
 * @qpair:      Pointer to the queue pair struct.
 *
 * This is the client interface for getting the amount of free
 * space in the QPair from the point of the view of the caller as
 * the producer which is the common case.  Returns < 0 if err, else
 * available bytes into which data can be enqueued if > 0.
 */
s64 vmci_qpair_produce_free_space(const struct vmci_qp *qpair)
{
        struct vmci_queue_header *produce_q_header;
        struct vmci_queue_header *consume_q_header;
        s64 result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);
        result =
            qp_get_queue_headers(qpair, &produce_q_header, &consume_q_header);
        if (result == VMCI_SUCCESS)
                result = vmci_q_header_free_space(produce_q_header,
                                                  consume_q_header,
                                                  qpair->produce_q_size);
        else
                result = 0;

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_produce_free_space);

/*
 * vmci_qpair_consume_free_space() - Retrieves free space in consumer queue.
 * @qpair:      Pointer to the queue pair struct.
 *
 * This is the client interface for getting the amount of free
 * space in the QPair from the point of the view of the caller as
 * the consumer which is not the common case.  Returns < 0 if err, else
 * available bytes into which data can be enqueued if > 0.
 */
s64 vmci_qpair_consume_free_space(const struct vmci_qp *qpair)
{
        struct vmci_queue_header *produce_q_header;
        struct vmci_queue_header *consume_q_header;
        s64 result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);
        result =
            qp_get_queue_headers(qpair, &produce_q_header, &consume_q_header);
        if (result == VMCI_SUCCESS)
                result = vmci_q_header_free_space(consume_q_header,
                                                  produce_q_header,
                                                  qpair->consume_q_size);
        else
                result = 0;

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_consume_free_space);

/*
 * vmci_qpair_produce_buf_ready() - Gets bytes ready to read from
 * producer queue.
 * @qpair:      Pointer to the queue pair struct.
 *
 * This is the client interface for getting the amount of
 * enqueued data in the QPair from the point of the view of the
 * caller as the producer which is not the common case.  Returns < 0 if err,
 * else available bytes that may be read.
 */
s64 vmci_qpair_produce_buf_ready(const struct vmci_qp *qpair)
{
        struct vmci_queue_header *produce_q_header;
        struct vmci_queue_header *consume_q_header;
        s64 result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);
        result =
            qp_get_queue_headers(qpair, &produce_q_header, &consume_q_header);
        if (result == VMCI_SUCCESS)
                result = vmci_q_header_buf_ready(produce_q_header,
                                                 consume_q_header,
                                                 qpair->produce_q_size);
        else
                result = 0;

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_produce_buf_ready);

/*
 * vmci_qpair_consume_buf_ready() - Gets bytes ready to read from
 * consumer queue.
 * @qpair:      Pointer to the queue pair struct.
 *
 * This is the client interface for getting the amount of
 * enqueued data in the QPair from the point of the view of the
 * caller as the consumer which is the normal case.  Returns < 0 if err,
 * else available bytes that may be read.
 */
s64 vmci_qpair_consume_buf_ready(const struct vmci_qp *qpair)
{
        struct vmci_queue_header *produce_q_header;
        struct vmci_queue_header *consume_q_header;
        s64 result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);
        result =
            qp_get_queue_headers(qpair, &produce_q_header, &consume_q_header);
        if (result == VMCI_SUCCESS)
                result = vmci_q_header_buf_ready(consume_q_header,
                                                 produce_q_header,
                                                 qpair->consume_q_size);
        else
                result = 0;

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_consume_buf_ready);

/*
 * vmci_qpair_enqueue() - Throw data on the queue.
 * @qpair:      Pointer to the queue pair struct.
 * @buf:        Pointer to buffer containing data
 * @buf_size:   Length of buffer.
 * @buf_type:   Buffer type (Unused).
 *
 * This is the client interface for enqueueing data into the queue.
 * Returns number of bytes enqueued or < 0 on error.
 */
ssize_t vmci_qpair_enqueue(struct vmci_qp *qpair,
                           const void *buf,
                           size_t buf_size,
                           int buf_type)
{
        ssize_t result;
        struct iov_iter from;
        struct kvec v = {.iov_base = (void *)buf, .iov_len = buf_size};

        if (!qpair || !buf)
                return VMCI_ERROR_INVALID_ARGS;

        iov_iter_kvec(&from, ITER_SOURCE, &v, 1, buf_size);

        qp_lock(qpair);

        do {
                result = qp_enqueue_locked(qpair->produce_q,
                                           qpair->consume_q,
                                           qpair->produce_q_size,
                                           &from);

                if (result == VMCI_ERROR_QUEUEPAIR_NOT_READY &&
                    !qp_wait_for_ready_queue(qpair))
                        result = VMCI_ERROR_WOULD_BLOCK;

        } while (result == VMCI_ERROR_QUEUEPAIR_NOT_READY);

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_enqueue);

/*
 * vmci_qpair_dequeue() - Get data from the queue.
 * @qpair:      Pointer to the queue pair struct.
 * @buf:        Pointer to buffer for the data
 * @buf_size:   Length of buffer.
 * @buf_type:   Buffer type (Unused).
 *
 * This is the client interface for dequeueing data from the queue.
 * Returns number of bytes dequeued or < 0 on error.
 */
ssize_t vmci_qpair_dequeue(struct vmci_qp *qpair,
                           void *buf,
                           size_t buf_size,
                           int buf_type)
{
        ssize_t result;
        struct iov_iter to;
        struct kvec v = {.iov_base = buf, .iov_len = buf_size};

        if (!qpair || !buf)
                return VMCI_ERROR_INVALID_ARGS;

        iov_iter_kvec(&to, ITER_DEST, &v, 1, buf_size);

        qp_lock(qpair);

        do {
                result = qp_dequeue_locked(qpair->produce_q,
                                           qpair->consume_q,
                                           qpair->consume_q_size,
                                           &to, true);

                if (result == VMCI_ERROR_QUEUEPAIR_NOT_READY &&
                    !qp_wait_for_ready_queue(qpair))
                        result = VMCI_ERROR_WOULD_BLOCK;

        } while (result == VMCI_ERROR_QUEUEPAIR_NOT_READY);

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_dequeue);

/*
 * vmci_qpair_peek() - Peek at the data in the queue.
 * @qpair:      Pointer to the queue pair struct.
 * @buf:        Pointer to buffer for the data
 * @buf_size:   Length of buffer.
 * @buf_type:   Buffer type (Unused on Linux).
 *
 * This is the client interface for peeking into a queue.  (I.e.,
 * copy data from the queue without updating the head pointer.)
 * Returns number of bytes dequeued or < 0 on error.
 */
ssize_t vmci_qpair_peek(struct vmci_qp *qpair,
                        void *buf,
                        size_t buf_size,
                        int buf_type)
{
        struct iov_iter to;
        struct kvec v = {.iov_base = buf, .iov_len = buf_size};
        ssize_t result;

        if (!qpair || !buf)
                return VMCI_ERROR_INVALID_ARGS;

        iov_iter_kvec(&to, ITER_DEST, &v, 1, buf_size);

        qp_lock(qpair);

        do {
                result = qp_dequeue_locked(qpair->produce_q,
                                           qpair->consume_q,
                                           qpair->consume_q_size,
                                           &to, false);

                if (result == VMCI_ERROR_QUEUEPAIR_NOT_READY &&
                    !qp_wait_for_ready_queue(qpair))
                        result = VMCI_ERROR_WOULD_BLOCK;

        } while (result == VMCI_ERROR_QUEUEPAIR_NOT_READY);

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_peek);

/*
 * vmci_qpair_enquev() - Throw data on the queue using iov.
 * @qpair:      Pointer to the queue pair struct.
 * @iov:        Pointer to buffer containing data
 * @iov_size:   Length of buffer.
 * @buf_type:   Buffer type (Unused).
 *
 * This is the client interface for enqueueing data into the queue.
 * This function uses IO vectors to handle the work. Returns number
 * of bytes enqueued or < 0 on error.
 */
ssize_t vmci_qpair_enquev(struct vmci_qp *qpair,
                          struct msghdr *msg,
                          size_t iov_size,
                          int buf_type)
{
        ssize_t result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);

        do {
                result = qp_enqueue_locked(qpair->produce_q,
                                           qpair->consume_q,
                                           qpair->produce_q_size,
                                           &msg->msg_iter);

                if (result == VMCI_ERROR_QUEUEPAIR_NOT_READY &&
                    !qp_wait_for_ready_queue(qpair))
                        result = VMCI_ERROR_WOULD_BLOCK;

        } while (result == VMCI_ERROR_QUEUEPAIR_NOT_READY);

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_enquev);

/*
 * vmci_qpair_dequev() - Get data from the queue using iov.
 * @qpair:      Pointer to the queue pair struct.
 * @iov:        Pointer to buffer for the data
 * @iov_size:   Length of buffer.
 * @buf_type:   Buffer type (Unused).
 *
 * This is the client interface for dequeueing data from the queue.
 * This function uses IO vectors to handle the work. Returns number
 * of bytes dequeued or < 0 on error.
 */
ssize_t vmci_qpair_dequev(struct vmci_qp *qpair,
                          struct msghdr *msg,
                          size_t iov_size,
                          int buf_type)
{
        ssize_t result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);

        do {
                result = qp_dequeue_locked(qpair->produce_q,
                                           qpair->consume_q,
                                           qpair->consume_q_size,
                                           &msg->msg_iter, true);

                if (result == VMCI_ERROR_QUEUEPAIR_NOT_READY &&
                    !qp_wait_for_ready_queue(qpair))
                        result = VMCI_ERROR_WOULD_BLOCK;

        } while (result == VMCI_ERROR_QUEUEPAIR_NOT_READY);

        qp_unlock(qpair);

        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_dequev);

/*
 * vmci_qpair_peekv() - Peek at the data in the queue using iov.
 * @qpair:      Pointer to the queue pair struct.
 * @iov:        Pointer to buffer for the data
 * @iov_size:   Length of buffer.
 * @buf_type:   Buffer type (Unused on Linux).
 *
 * This is the client interface for peeking into a queue.  (I.e.,
 * copy data from the queue without updating the head pointer.)
 * This function uses IO vectors to handle the work. Returns number
 * of bytes peeked or < 0 on error.
 */
ssize_t vmci_qpair_peekv(struct vmci_qp *qpair,
                         struct msghdr *msg,
                         size_t iov_size,
                         int buf_type)
{
        ssize_t result;

        if (!qpair)
                return VMCI_ERROR_INVALID_ARGS;

        qp_lock(qpair);

        do {
                result = qp_dequeue_locked(qpair->produce_q,
                                           qpair->consume_q,
                                           qpair->consume_q_size,
                                           &msg->msg_iter, false);

                if (result == VMCI_ERROR_QUEUEPAIR_NOT_READY &&
                    !qp_wait_for_ready_queue(qpair))
                        result = VMCI_ERROR_WOULD_BLOCK;

        } while (result == VMCI_ERROR_QUEUEPAIR_NOT_READY);

        qp_unlock(qpair);
        return result;
}
EXPORT_SYMBOL_GPL(vmci_qpair_peekv);