diff --git a/include/qemu/vfio-helpers.h b/include/qemu/vfio-helpers.h
new file mode 100644
index 0000000000..ce7e7b057f
--- /dev/null
+++ b/include/qemu/vfio-helpers.h
@@ -0,0 +1,33 @@
+/*
+ * QEMU VFIO helpers
+ *
+ * Copyright 2016 - 2018 Red Hat, Inc.
+ *
+ * Authors:
+ *   Fam Zheng <famz@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef QEMU_VFIO_HELPERS_H
+#define QEMU_VFIO_HELPERS_H
+#include "qemu/typedefs.h"
+
+typedef struct QEMUVFIOState QEMUVFIOState;
+
+QEMUVFIOState *qemu_vfio_open_pci(const char *device, Error **errp);
+void qemu_vfio_close(QEMUVFIOState *s);
+int qemu_vfio_dma_map(QEMUVFIOState *s, void *host, size_t size,
+                      bool temporary, uint64_t *iova_list);
+int qemu_vfio_dma_reset_temporary(QEMUVFIOState *s);
+void qemu_vfio_dma_unmap(QEMUVFIOState *s, void *host);
+void *qemu_vfio_pci_map_bar(QEMUVFIOState *s, int index,
+                            uint64_t offset, uint64_t size,
+                            Error **errp);
+void qemu_vfio_pci_unmap_bar(QEMUVFIOState *s, int index, void *bar,
+                             uint64_t offset, uint64_t size);
+int qemu_vfio_pci_init_irq(QEMUVFIOState *s, EventNotifier *e,
+                           int irq_type, Error **errp);
+
+#endif
diff --git a/util/Makefile.objs b/util/Makefile.objs
index 2973b0a323..3fb611631f 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -46,3 +46,4 @@ util-obj-y += qht.o
 util-obj-y += range.o
 util-obj-y += stats64.o
 util-obj-y += systemd.o
+util-obj-$(CONFIG_LINUX) += vfio-helpers.o
diff --git a/util/trace-events b/util/trace-events
index 515e6257fb..4822434c89 100644
--- a/util/trace-events
+++ b/util/trace-events
@@ -60,3 +60,14 @@ lockcnt_futex_wake(const void *lockcnt) "lockcnt %p waking up one waiter"
 qemu_mutex_lock(void *mutex, const char *file, const int line) "waiting on mutex %p (%s:%d)"
 qemu_mutex_locked(void *mutex, const char *file, const int line) "taken mutex %p (%s:%d)"
 qemu_mutex_unlock(void *mutex, const char *file, const int line) "released mutex %p (%s:%d)"
+
+# util/vfio-helpers.c
+qemu_vfio_dma_reset_temporary(void *s) "s %p"
+qemu_vfio_ram_block_added(void *s, void *p, size_t size) "s %p host %p size 0x%zx"
+qemu_vfio_ram_block_removed(void *s, void *p, size_t size) "s %p host %p size 0x%zx"
+qemu_vfio_find_mapping(void *s, void *p) "s %p host %p"
+qemu_vfio_new_mapping(void *s, void *host, size_t size, int index, uint64_t iova) "s %p host %p size %zu index %d iova 0x%"PRIx64
+qemu_vfio_do_mapping(void *s, void *host, size_t size, uint64_t iova) "s %p host %p size %zu iova 0x%"PRIx64
+qemu_vfio_dma_map(void *s, void *host, size_t size, bool temporary, uint64_t *iova) "s %p host %p size %zu temporary %d iova %p"
+qemu_vfio_dma_map_invalid(void *s, void *mapping_host, size_t mapping_size, void *host, size_t size) "s %p mapping %p %zu requested %p %zu"
+qemu_vfio_dma_unmap(void *s, void *host) "s %p host %p"
diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
new file mode 100644
index 0000000000..0660aaf2f7
--- /dev/null
+++ b/util/vfio-helpers.c
@@ -0,0 +1,726 @@
+/*
+ * VFIO utility
+ *
+ * Copyright 2016 - 2018 Red Hat, Inc.
+ *
+ * Authors:
+ *   Fam Zheng <famz@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include <sys/ioctl.h>
+#include <linux/vfio.h>
+#include "qapi/error.h"
+#include "exec/ramlist.h"
+#include "exec/cpu-common.h"
+#include "trace.h"
+#include "qemu/queue.h"
+#include "qemu/error-report.h"
+#include "standard-headers/linux/pci_regs.h"
+#include "qemu/event_notifier.h"
+#include "qemu/vfio-helpers.h"
+#include "trace.h"
+
+#define QEMU_VFIO_DEBUG 0
+
+#define QEMU_VFIO_IOVA_MIN 0x10000ULL
+/* XXX: Once VFIO exposes the iova bit width in the IOMMU capability interface,
+ * we can use a runtime limit; alternatively it's also possible to do platform
+ * specific detection by reading sysfs entries. Until then, 39 is a safe bet.
+ **/
+#define QEMU_VFIO_IOVA_MAX (1ULL << 39)
+
+typedef struct {
+    /* Page aligned addr. */
+    void *host;
+    size_t size;
+    uint64_t iova;
+} IOVAMapping;
+
+struct QEMUVFIOState {
+    QemuMutex lock;
+
+    /* These fields are protected by BQL */
+    int container;
+    int group;
+    int device;
+    RAMBlockNotifier ram_notifier;
+    struct vfio_region_info config_region_info, bar_region_info[6];
+
+    /* These fields are protected by @lock */
+    /* VFIO's IO virtual address space is managed by splitting into a few
+     * sections:
+     *
+     * ---------------       <= 0
+     * |xxxxxxxxxxxxx|
+     * |-------------|       <= QEMU_VFIO_IOVA_MIN
+     * |             |
+     * |    Fixed    |
+     * |             |
+     * |-------------|       <= low_water_mark
+     * |             |
+     * |    Free     |
+     * |             |
+     * |-------------|       <= high_water_mark
+     * |             |
+     * |    Temp     |
+     * |             |
+     * |-------------|       <= QEMU_VFIO_IOVA_MAX
+     * |xxxxxxxxxxxxx|
+     * |xxxxxxxxxxxxx|
+     * ---------------
+     *
+     * - Addresses lower than QEMU_VFIO_IOVA_MIN are reserved as invalid;
+     *
+     * - Fixed mappings of HVAs are assigned "low" IOVAs in the range of
+     *   [QEMU_VFIO_IOVA_MIN, low_water_mark).  Once allocated they will not be
+     *   reclaimed - low_water_mark never shrinks;
+     *
+     * - IOVAs in range [low_water_mark, high_water_mark) are free;
+     *
+     * - IOVAs in range [high_water_mark, QEMU_VFIO_IOVA_MAX) are volatile
+     *   mappings. At each qemu_vfio_dma_reset_temporary() call, the whole area
+     *   is recycled. The caller should make sure I/O's depending on these
+     *   mappings are completed before calling.
+     **/
+    uint64_t low_water_mark;
+    uint64_t high_water_mark;
+    IOVAMapping *mappings;
+    int nr_mappings;
+};
+
+/**
+ * Find group file by PCI device address as specified @device, and return the
+ * path. The returned string is owned by caller and should be g_free'ed later.
+ */
+static char *sysfs_find_group_file(const char *device, Error **errp)
+{
+    char *sysfs_link;
+    char *sysfs_group;
+    char *p;
+    char *path = NULL;
+
+    sysfs_link = g_strdup_printf("/sys/bus/pci/devices/%s/iommu_group", device);
+    sysfs_group = g_malloc(PATH_MAX);
+    if (readlink(sysfs_link, sysfs_group, PATH_MAX - 1) == -1) {
+        error_setg_errno(errp, errno, "Failed to find iommu group sysfs path");
+        goto out;
+    }
+    p = strrchr(sysfs_group, '/');
+    if (!p) {
+        error_setg(errp, "Failed to find iommu group number");
+        goto out;
+    }
+
+    path = g_strdup_printf("/dev/vfio/%s", p + 1);
+out:
+    g_free(sysfs_link);
+    g_free(sysfs_group);
+    return path;
+}
+
+static inline void assert_bar_index_valid(QEMUVFIOState *s, int index)
+{
+    assert(index >= 0 && index < ARRAY_SIZE(s->bar_region_info));
+}
+
+static int qemu_vfio_pci_init_bar(QEMUVFIOState *s, int index, Error **errp)
+{
+    assert_bar_index_valid(s, index);
+    s->bar_region_info[index] = (struct vfio_region_info) {
+        .index = VFIO_PCI_BAR0_REGION_INDEX + index,
+        .argsz = sizeof(struct vfio_region_info),
+    };
+    if (ioctl(s->device, VFIO_DEVICE_GET_REGION_INFO, &s->bar_region_info[index])) {
+        error_setg_errno(errp, errno, "Failed to get BAR region info");
+        return -errno;
+    }
+
+    return 0;
+}
+
+/**
+ * Map a PCI bar area.
+ */
+void *qemu_vfio_pci_map_bar(QEMUVFIOState *s, int index,
+                            uint64_t offset, uint64_t size,
+                            Error **errp)
+{
+    void *p;
+    assert_bar_index_valid(s, index);
+    p = mmap(NULL, MIN(size, s->bar_region_info[index].size - offset),
+             PROT_READ | PROT_WRITE, MAP_SHARED,
+             s->device, s->bar_region_info[index].offset + offset);
+    if (p == MAP_FAILED) {
+        error_setg_errno(errp, errno, "Failed to map BAR region");
+        p = NULL;
+    }
+    return p;
+}
+
+/**
+ * Unmap a PCI bar area.
+ */
+void qemu_vfio_pci_unmap_bar(QEMUVFIOState *s, int index, void *bar,
+                             uint64_t offset, uint64_t size)
+{
+    if (bar) {
+        munmap(bar, MIN(size, s->bar_region_info[index].size - offset));
+    }
+}
+
+/**
+ * Initialize device IRQ with @irq_type and and register an event notifier.
+ */
+int qemu_vfio_pci_init_irq(QEMUVFIOState *s, EventNotifier *e,
+                           int irq_type, Error **errp)
+{
+    int r;
+    struct vfio_irq_set *irq_set;
+    size_t irq_set_size;
+    struct vfio_irq_info irq_info = { .argsz = sizeof(irq_info) };
+
+    irq_info.index = irq_type;
+    if (ioctl(s->device, VFIO_DEVICE_GET_IRQ_INFO, &irq_info)) {
+        error_setg_errno(errp, errno, "Failed to get device interrupt info");
+        return -errno;
+    }
+    if (!(irq_info.flags & VFIO_IRQ_INFO_EVENTFD)) {
+        error_setg(errp, "Device interrupt doesn't support eventfd");
+        return -EINVAL;
+    }
+
+    irq_set_size = sizeof(*irq_set) + sizeof(int);
+    irq_set = g_malloc0(irq_set_size);
+
+    /* Get to a known IRQ state */
+    *irq_set = (struct vfio_irq_set) {
+        .argsz = irq_set_size,
+        .flags = VFIO_IRQ_SET_DATA_EVENTFD | VFIO_IRQ_SET_ACTION_TRIGGER,
+        .index = irq_info.index,
+        .start = 0,
+        .count = 1,
+    };
+
+    *(int *)&irq_set->data = event_notifier_get_fd(e);
+    r = ioctl(s->device, VFIO_DEVICE_SET_IRQS, irq_set);
+    g_free(irq_set);
+    if (r) {
+        error_setg_errno(errp, errno, "Failed to setup device interrupt");
+        return -errno;
+    }
+    return 0;
+}
+
+static int qemu_vfio_pci_read_config(QEMUVFIOState *s, void *buf,
+                                     int size, int ofs)
+{
+    int ret;
+
+    do {
+        ret = pread(s->device, buf, size, s->config_region_info.offset + ofs);
+    } while (ret == -1 && errno == EINTR);
+    return ret == size ? 0 : -errno;
+}
+
+static int qemu_vfio_pci_write_config(QEMUVFIOState *s, void *buf, int size, int ofs)
+{
+    int ret;
+
+    do {
+        ret = pwrite(s->device, buf, size, s->config_region_info.offset + ofs);
+    } while (ret == -1 && errno == EINTR);
+    return ret == size ? 0 : -errno;
+}
+
+static int qemu_vfio_init_pci(QEMUVFIOState *s, const char *device,
+                              Error **errp)
+{
+    int ret;
+    int i;
+    uint16_t pci_cmd;
+    struct vfio_group_status group_status = { .argsz = sizeof(group_status) };
+    struct vfio_iommu_type1_info iommu_info = { .argsz = sizeof(iommu_info) };
+    struct vfio_device_info device_info = { .argsz = sizeof(device_info) };
+    char *group_file = NULL;
+
+    /* Create a new container */
+    s->container = open("/dev/vfio/vfio", O_RDWR);
+
+    if (s->container == -1) {
+        error_setg_errno(errp, errno, "Failed to open /dev/vfio/vfio");
+        return -errno;
+    }
+    if (ioctl(s->container, VFIO_GET_API_VERSION) != VFIO_API_VERSION) {
+        error_setg(errp, "Invalid VFIO version");
+        ret = -EINVAL;
+        goto fail_container;
+    }
+
+    if (!ioctl(s->container, VFIO_CHECK_EXTENSION, VFIO_TYPE1_IOMMU)) {
+        error_setg_errno(errp, errno, "VFIO IOMMU check failed");
+        ret = -EINVAL;
+        goto fail_container;
+    }
+
+    /* Open the group */
+    group_file = sysfs_find_group_file(device, errp);
+    if (!group_file) {
+        ret = -EINVAL;
+        goto fail_container;
+    }
+
+    s->group = open(group_file, O_RDWR);
+    if (s->group == -1) {
+        error_setg_errno(errp, errno, "Failed to open VFIO group file: %s",
+                         group_file);
+        g_free(group_file);
+        ret = -errno;
+        goto fail_container;
+    }
+    g_free(group_file);
+
+    /* Test the group is viable and available */
+    if (ioctl(s->group, VFIO_GROUP_GET_STATUS, &group_status)) {
+        error_setg_errno(errp, errno, "Failed to get VFIO group status");
+        ret = -errno;
+        goto fail;
+    }
+
+    if (!(group_status.flags & VFIO_GROUP_FLAGS_VIABLE)) {
+        error_setg(errp, "VFIO group is not viable");
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* Add the group to the container */
+    if (ioctl(s->group, VFIO_GROUP_SET_CONTAINER, &s->container)) {
+        error_setg_errno(errp, errno, "Failed to add group to VFIO container");
+        ret = -errno;
+        goto fail;
+    }
+
+    /* Enable the IOMMU model we want */
+    if (ioctl(s->container, VFIO_SET_IOMMU, VFIO_TYPE1_IOMMU)) {
+        error_setg_errno(errp, errno, "Failed to set VFIO IOMMU type");
+        ret = -errno;
+        goto fail;
+    }
+
+    /* Get additional IOMMU info */
+    if (ioctl(s->container, VFIO_IOMMU_GET_INFO, &iommu_info)) {
+        error_setg_errno(errp, errno, "Failed to get IOMMU info");
+        ret = -errno;
+        goto fail;
+    }
+
+    s->device = ioctl(s->group, VFIO_GROUP_GET_DEVICE_FD, device);
+
+    if (s->device < 0) {
+        error_setg_errno(errp, errno, "Failed to get device fd");
+        ret = -errno;
+        goto fail;
+    }
+
+    /* Test and setup the device */
+    if (ioctl(s->device, VFIO_DEVICE_GET_INFO, &device_info)) {
+        error_setg_errno(errp, errno, "Failed to get device info");
+        ret = -errno;
+        goto fail;
+    }
+
+    if (device_info.num_regions < VFIO_PCI_CONFIG_REGION_INDEX) {
+        error_setg(errp, "Invalid device regions");
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    s->config_region_info = (struct vfio_region_info) {
+        .index = VFIO_PCI_CONFIG_REGION_INDEX,
+        .argsz = sizeof(struct vfio_region_info),
+    };
+    if (ioctl(s->device, VFIO_DEVICE_GET_REGION_INFO, &s->config_region_info)) {
+        error_setg_errno(errp, errno, "Failed to get config region info");
+        ret = -errno;
+        goto fail;
+    }
+
+    for (i = 0; i < 6; i++) {
+        ret = qemu_vfio_pci_init_bar(s, i, errp);
+        if (ret) {
+            goto fail;
+        }
+    }
+
+    /* Enable bus master */
+    ret = qemu_vfio_pci_read_config(s, &pci_cmd, sizeof(pci_cmd), PCI_COMMAND);
+    if (ret) {
+        goto fail;
+    }
+    pci_cmd |= PCI_COMMAND_MASTER;
+    ret = qemu_vfio_pci_write_config(s, &pci_cmd, sizeof(pci_cmd), PCI_COMMAND);
+    if (ret) {
+        goto fail;
+    }
+    return 0;
+fail:
+    close(s->group);
+fail_container:
+    close(s->container);
+    return ret;
+}
+
+static void qemu_vfio_ram_block_added(RAMBlockNotifier *n,
+                                      void *host, size_t size)
+{
+    QEMUVFIOState *s = container_of(n, QEMUVFIOState, ram_notifier);
+    trace_qemu_vfio_ram_block_added(s, host, size);
+    qemu_vfio_dma_map(s, host, size, false, NULL);
+}
+
+static void qemu_vfio_ram_block_removed(RAMBlockNotifier *n,
+                                        void *host, size_t size)
+{
+    QEMUVFIOState *s = container_of(n, QEMUVFIOState, ram_notifier);
+    if (host) {
+        trace_qemu_vfio_ram_block_removed(s, host, size);
+        qemu_vfio_dma_unmap(s, host);
+    }
+}
+
+static int qemu_vfio_init_ramblock(const char *block_name, void *host_addr,
+                                   ram_addr_t offset, ram_addr_t length,
+                                   void *opaque)
+{
+    int ret;
+    QEMUVFIOState *s = opaque;
+
+    if (!host_addr) {
+        return 0;
+    }
+    ret = qemu_vfio_dma_map(s, host_addr, length, false, NULL);
+    if (ret) {
+        fprintf(stderr, "qemu_vfio_init_ramblock: failed %p %ld\n",
+                host_addr, length);
+    }
+    return 0;
+}
+
+static void qemu_vfio_open_common(QEMUVFIOState *s)
+{
+    s->ram_notifier.ram_block_added = qemu_vfio_ram_block_added;
+    s->ram_notifier.ram_block_removed = qemu_vfio_ram_block_removed;
+    ram_block_notifier_add(&s->ram_notifier);
+    s->low_water_mark = QEMU_VFIO_IOVA_MIN;
+    s->high_water_mark = QEMU_VFIO_IOVA_MAX;
+    qemu_ram_foreach_block(qemu_vfio_init_ramblock, s);
+    qemu_mutex_init(&s->lock);
+}
+
+/**
+ * Open a PCI device, e.g. "0000:00:01.0".
+ */
+QEMUVFIOState *qemu_vfio_open_pci(const char *device, Error **errp)
+{
+    int r;
+    QEMUVFIOState *s = g_new0(QEMUVFIOState, 1);
+
+    r = qemu_vfio_init_pci(s, device, errp);
+    if (r) {
+        g_free(s);
+        return NULL;
+    }
+    qemu_vfio_open_common(s);
+    return s;
+}
+
+static void qemu_vfio_dump_mapping(IOVAMapping *m)
+{
+    if (QEMU_VFIO_DEBUG) {
+        printf("  vfio mapping %p %lx to %lx\n", m->host, m->size, m->iova);
+    }
+}
+
+static void qemu_vfio_dump_mappings(QEMUVFIOState *s)
+{
+    int i;
+
+    if (QEMU_VFIO_DEBUG) {
+        printf("vfio mappings\n");
+        for (i = 0; i < s->nr_mappings; ++i) {
+            qemu_vfio_dump_mapping(&s->mappings[i]);
+        }
+    }
+}
+
+/**
+ * Find the mapping entry that contains [host, host + size) and set @index to
+ * the position. If no entry contains it, @index is the position _after_ which
+ * to insert the new mapping. IOW, it is the index of the largest element that
+ * is smaller than @host, or -1 if no entry is.
+ */
+static IOVAMapping *qemu_vfio_find_mapping(QEMUVFIOState *s, void *host,
+                                           int *index)
+{
+    IOVAMapping *p = s->mappings;
+    IOVAMapping *q = p ? p + s->nr_mappings - 1 : NULL;
+    IOVAMapping *mid;
+    trace_qemu_vfio_find_mapping(s, host);
+    if (!p) {
+        *index = -1;
+        return NULL;
+    }
+    while (true) {
+        mid = p + (q - p) / 2;
+        if (mid == p) {
+            break;
+        }
+        if (mid->host > host) {
+            q = mid;
+        } else if (mid->host < host) {
+            p = mid;
+        } else {
+            break;
+        }
+    }
+    if (mid->host > host) {
+        mid--;
+    } else if (mid < &s->mappings[s->nr_mappings - 1]
+               && (mid + 1)->host <= host) {
+        mid++;
+    }
+    *index = mid - &s->mappings[0];
+    if (mid >= &s->mappings[0] &&
+        mid->host <= host && mid->host + mid->size > host) {
+        assert(mid < &s->mappings[s->nr_mappings]);
+        return mid;
+    }
+    /* At this point *index + 1 is the right position to insert the new
+     * mapping.*/
+    return NULL;
+}
+
+/**
+ * Allocate IOVA and and create a new mapping record and insert it in @s.
+ */
+static IOVAMapping *qemu_vfio_add_mapping(QEMUVFIOState *s,
+                                          void *host, size_t size,
+                                          int index, uint64_t iova)
+{
+    int shift;
+    IOVAMapping m = {.host = host, .size = size, iova = iova};
+    IOVAMapping *insert;
+
+    assert(QEMU_IS_ALIGNED(size, getpagesize()));
+    assert(QEMU_IS_ALIGNED(s->low_water_mark, getpagesize()));
+    assert(QEMU_IS_ALIGNED(s->high_water_mark, getpagesize()));
+    trace_qemu_vfio_new_mapping(s, host, size, index, iova);
+
+    assert(index >= 0);
+    s->nr_mappings++;
+    s->mappings = g_realloc_n(s->mappings, sizeof(s->mappings[0]),
+                              s->nr_mappings);
+    insert = &s->mappings[index];
+    shift = s->nr_mappings - index - 1;
+    if (shift) {
+        memmove(insert + 1, insert, shift * sizeof(s->mappings[0]));
+    }
+    *insert = m;
+    return insert;
+}
+
+/* Do the DMA mapping with VFIO. */
+static int qemu_vfio_do_mapping(QEMUVFIOState *s, void *host, size_t size,
+                                uint64_t iova)
+{
+    struct vfio_iommu_type1_dma_map dma_map = {
+        .argsz = sizeof(dma_map),
+        .flags = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE,
+        .iova = iova,
+        .vaddr = (uintptr_t)host,
+        .size = size,
+    };
+    trace_qemu_vfio_do_mapping(s, host, size, iova);
+
+    if (ioctl(s->container, VFIO_IOMMU_MAP_DMA, &dma_map)) {
+        error_report("VFIO_MAP_DMA: %d", -errno);
+        return -errno;
+    }
+    return 0;
+}
+
+/**
+ * Undo the DMA mapping from @s with VFIO, and remove from mapping list.
+ */
+static void qemu_vfio_undo_mapping(QEMUVFIOState *s, IOVAMapping *mapping,
+                                   Error **errp)
+{
+    int index;
+    struct vfio_iommu_type1_dma_unmap unmap = {
+        .argsz = sizeof(unmap),
+        .flags = 0,
+        .iova = mapping->iova,
+        .size = mapping->size,
+    };
+
+    index = mapping - s->mappings;
+    assert(mapping->size > 0);
+    assert(QEMU_IS_ALIGNED(mapping->size, getpagesize()));
+    assert(index >= 0 && index < s->nr_mappings);
+    if (ioctl(s->container, VFIO_IOMMU_UNMAP_DMA, &unmap)) {
+        error_setg(errp, "VFIO_UNMAP_DMA failed: %d", -errno);
+    }
+    memmove(mapping, &s->mappings[index + 1],
+            sizeof(s->mappings[0]) * (s->nr_mappings - index - 1));
+    s->nr_mappings--;
+    s->mappings = g_realloc_n(s->mappings, sizeof(s->mappings[0]),
+                              s->nr_mappings);
+}
+
+/* Check if the mapping list is (ascending) ordered. */
+static bool qemu_vfio_verify_mappings(QEMUVFIOState *s)
+{
+    int i;
+    if (QEMU_VFIO_DEBUG) {
+        for (i = 0; i < s->nr_mappings - 1; ++i) {
+            if (!(s->mappings[i].host < s->mappings[i + 1].host)) {
+                fprintf(stderr, "item %d not sorted!\n", i);
+                qemu_vfio_dump_mappings(s);
+                return false;
+            }
+            if (!(s->mappings[i].host + s->mappings[i].size <=
+                  s->mappings[i + 1].host)) {
+                fprintf(stderr, "item %d overlap with next!\n", i);
+                qemu_vfio_dump_mappings(s);
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
+/* Map [host, host + size) area into a contiguous IOVA address space, and store
+ * the result in @iova if not NULL. The caller need to make sure the area is
+ * aligned to page size, and mustn't overlap with existing mapping areas (split
+ * mapping status within this area is not allowed).
+ */
+int qemu_vfio_dma_map(QEMUVFIOState *s, void *host, size_t size,
+                      bool temporary, uint64_t *iova)
+{
+    int ret = 0;
+    int index;
+    IOVAMapping *mapping;
+    uint64_t iova0;
+
+    assert(QEMU_PTR_IS_ALIGNED(host, getpagesize()));
+    assert(QEMU_IS_ALIGNED(size, getpagesize()));
+    trace_qemu_vfio_dma_map(s, host, size, temporary, iova);
+    qemu_mutex_lock(&s->lock);
+    mapping = qemu_vfio_find_mapping(s, host, &index);
+    if (mapping) {
+        iova0 = mapping->iova + ((uint8_t *)host - (uint8_t *)mapping->host);
+    } else {
+        if (s->high_water_mark - s->low_water_mark + 1 < size) {
+            ret = -ENOMEM;
+            goto out;
+        }
+        if (!temporary) {
+            iova0 = s->low_water_mark;
+            mapping = qemu_vfio_add_mapping(s, host, size, index + 1, iova0);
+            if (!mapping) {
+                ret = -ENOMEM;
+                goto out;
+            }
+            assert(qemu_vfio_verify_mappings(s));
+            ret = qemu_vfio_do_mapping(s, host, size, iova0);
+            if (ret) {
+                qemu_vfio_undo_mapping(s, mapping, NULL);
+                goto out;
+            }
+            s->low_water_mark += size;
+            qemu_vfio_dump_mappings(s);
+        } else {
+            iova0 = s->high_water_mark - size;
+            ret = qemu_vfio_do_mapping(s, host, size, iova0);
+            if (ret) {
+                goto out;
+            }
+            s->high_water_mark -= size;
+        }
+    }
+    if (iova) {
+        *iova = iova0;
+    }
+out:
+    qemu_mutex_unlock(&s->lock);
+    return ret;
+}
+
+/* Reset the high watermark and free all "temporary" mappings. */
+int qemu_vfio_dma_reset_temporary(QEMUVFIOState *s)
+{
+    struct vfio_iommu_type1_dma_unmap unmap = {
+        .argsz = sizeof(unmap),
+        .flags = 0,
+        .iova = s->high_water_mark,
+        .size = QEMU_VFIO_IOVA_MAX - s->high_water_mark,
+    };
+    trace_qemu_vfio_dma_reset_temporary(s);
+    qemu_mutex_lock(&s->lock);
+    if (ioctl(s->container, VFIO_IOMMU_UNMAP_DMA, &unmap)) {
+        error_report("VFIO_UNMAP_DMA: %d", -errno);
+        qemu_mutex_unlock(&s->lock);
+        return -errno;
+    }
+    s->high_water_mark = QEMU_VFIO_IOVA_MAX;
+    qemu_mutex_unlock(&s->lock);
+    return 0;
+}
+
+/* Unmapping the whole area that was previously mapped with
+ * qemu_vfio_dma_map(). */
+void qemu_vfio_dma_unmap(QEMUVFIOState *s, void *host)
+{
+    int index = 0;
+    IOVAMapping *m;
+
+    if (!host) {
+        return;
+    }
+
+    trace_qemu_vfio_dma_unmap(s, host);
+    qemu_mutex_lock(&s->lock);
+    m = qemu_vfio_find_mapping(s, host, &index);
+    if (!m) {
+        goto out;
+    }
+    qemu_vfio_undo_mapping(s, m, NULL);
+out:
+    qemu_mutex_unlock(&s->lock);
+}
+
+static void qemu_vfio_reset(QEMUVFIOState *s)
+{
+    ioctl(s->device, VFIO_DEVICE_RESET);
+}
+
+/* Close and free the VFIO resources. */
+void qemu_vfio_close(QEMUVFIOState *s)
+{
+    int i;
+
+    if (!s) {
+        return;
+    }
+    for (i = 0; i < s->nr_mappings; ++i) {
+        qemu_vfio_undo_mapping(s, &s->mappings[i], NULL);
+    }
+    ram_block_notifier_remove(&s->ram_notifier);
+    qemu_vfio_reset(s);
+    close(s->device);
+    close(s->group);
+    close(s->container);
+}
