[v7,4/7] Add memfd based hostmem

diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
new file mode 100644
index 0000000000..1e20fe0ba8
--- /dev/null
+++ b/backends/hostmem-memfd.c
@@ -0,0 +1,170 @@ 
+/*
+ * QEMU host memfd memory backend
+ *
+ * Copyright (C) 2018 Red Hat Inc
+ *
+ * Authors:
+ *   Marc-André Lureau <marcandre.lureau@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 "qemu-common.h"
+#include "sysemu/hostmem.h"
+#include "sysemu/sysemu.h"
+#include "qom/object_interfaces.h"
+#include "qemu/memfd.h"
+#include "qapi/error.h"
+
+#define TYPE_MEMORY_BACKEND_MEMFD "memory-backend-memfd"
+
+#define MEMORY_BACKEND_MEMFD(obj)                                        \
+    OBJECT_CHECK(HostMemoryBackendMemfd, (obj), TYPE_MEMORY_BACKEND_MEMFD)
+
+typedef struct HostMemoryBackendMemfd HostMemoryBackendMemfd;
+
+struct HostMemoryBackendMemfd {
+    HostMemoryBackend parent_obj;
+
+    bool hugetlb;
+    uint64_t hugetlbsize;
+    bool seal;
+};
+
+static void
+memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
+{
+    HostMemoryBackendMemfd *m = MEMORY_BACKEND_MEMFD(backend);
+    char *name;
+    int fd;
+
+    if (!backend->size) {
+        error_setg(errp, "can't create backend with size 0");
+        return;
+    }
+
+    if (host_memory_backend_mr_inited(backend)) {
+        return;
+    }
+
+    backend->force_prealloc = mem_prealloc;
+    fd = qemu_memfd_create(TYPE_MEMORY_BACKEND_MEMFD, backend->size,
+                           m->hugetlb, m->hugetlbsize, m->seal ?
+                           F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL : 0,
+                           errp);
+    if (fd == -1) {
+        return;
+    }
+
+    name = object_get_canonical_path(OBJECT(backend));
+    memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
+                                   name, backend->size, true, fd, errp);
+    g_free(name);
+}
+
+static bool
+memfd_backend_get_hugetlb(Object *o, Error **errp)
+{
+    return MEMORY_BACKEND_MEMFD(o)->hugetlb;
+}
+
+static void
+memfd_backend_set_hugetlb(Object *o, bool value, Error **errp)
+{
+    MEMORY_BACKEND_MEMFD(o)->hugetlb = value;
+}
+
+static void
+memfd_backend_set_hugetlbsize(Object *obj, Visitor *v, const char *name,
+                              void *opaque, Error **errp)
+{
+    HostMemoryBackendMemfd *m = MEMORY_BACKEND_MEMFD(obj);
+    Error *local_err = NULL;
+    uint64_t value;
+
+    if (host_memory_backend_mr_inited(MEMORY_BACKEND(obj))) {
+        error_setg(&local_err, "cannot change property value");
+        goto out;
+    }
+
+    visit_type_size(v, name, &value, &local_err);
+    if (local_err) {
+        goto out;
+    }
+    if (!value) {
+        error_setg(&local_err, "Property '%s.%s' doesn't take value '%"
+                   PRIu64 "'", object_get_typename(obj), name, value);
+        goto out;
+    }
+    m->hugetlbsize = value;
+out:
+    error_propagate(errp, local_err);
+}
+
+static void
+memfd_backend_get_hugetlbsize(Object *obj, Visitor *v, const char *name,
+                              void *opaque, Error **errp)
+{
+    HostMemoryBackendMemfd *m = MEMORY_BACKEND_MEMFD(obj);
+    uint64_t value = m->hugetlbsize;
+
+    visit_type_size(v, name, &value, errp);
+}
+
+static bool
+memfd_backend_get_seal(Object *o, Error **errp)
+{
+    return MEMORY_BACKEND_MEMFD(o)->seal;
+}
+
+static void
+memfd_backend_set_seal(Object *o, bool value, Error **errp)
+{
+    MEMORY_BACKEND_MEMFD(o)->seal = value;
+}
+
+static void
+memfd_backend_instance_init(Object *obj)
+{
+    HostMemoryBackendMemfd *m = MEMORY_BACKEND_MEMFD(obj);
+
+    /* default to sealed file */
+    m->seal = true;
+}
+
+static void
+memfd_backend_class_init(ObjectClass *oc, void *data)
+{
+    HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
+
+    bc->alloc = memfd_backend_memory_alloc;
+
+    object_class_property_add_bool(oc, "hugetlb",
+                                   memfd_backend_get_hugetlb,
+                                   memfd_backend_set_hugetlb,
+                                   &error_abort);
+    object_class_property_add(oc, "hugetlbsize", "int",
+                              memfd_backend_get_hugetlbsize,
+                              memfd_backend_set_hugetlbsize,
+                              NULL, NULL, &error_abort);
+    object_class_property_add_bool(oc, "seal",
+                                   memfd_backend_get_seal,
+                                   memfd_backend_set_seal,
+                                   &error_abort);
+}
+
+static const TypeInfo memfd_backend_info = {
+    .name = TYPE_MEMORY_BACKEND_MEMFD,
+    .parent = TYPE_MEMORY_BACKEND,
+    .instance_init = memfd_backend_instance_init,
+    .class_init = memfd_backend_class_init,
+    .instance_size = sizeof(HostMemoryBackendMemfd),
+};
+
+static void register_types(void)
+{
+    type_register_static(&memfd_backend_info);
+}
+
+type_init(register_types);
diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index 0400799efd..67eeeba5fc 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -8,3 +8,5 @@  common-obj-$(CONFIG_LINUX) += hostmem-file.o
 
 common-obj-y += cryptodev.o
 common-obj-y += cryptodev-builtin.o
+
+common-obj-$(CONFIG_LINUX) += hostmem-memfd.o
diff --git a/qemu-options.hx b/qemu-options.hx
index 8ce427da78..265cf9fa38 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4024,6 +4024,28 @@  Memory backend objects offer more control than the @option{-m} option that is
 traditionally used to define guest RAM. Please refer to
 @option{memory-backend-file} for a description of the options.
 
+@item -object memory-backend-memfd,id=@var{id},merge=@var{on|off},dump=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave},seal=@var{on|off},hugetlb=@var{on|off},hugetlbsize=@var{size}
+
+Creates an anonymous memory file backend object, which allows QEMU to
+share the memory with an external process (e.g. when using
+vhost-user). The memory is allocated with memfd and optional
+sealing. (Linux only)
+
+The @option{seal} option creates a sealed-file, that will block
+further resizing the memory ('on' by default).
+
+The @option{hugetlb} option specify the file to be created resides in
+the hugetlbfs filesystem (since Linux 4.14).  Used in conjunction with
+the @option{hugetlb} option, the @option{hugetlbsize} option specify
+the hugetlb page size on systems that support multiple hugetlb page
+sizes (it must be a power of 2 value supported by the system).
+
+In some versions of Linux, the @option{hugetlb} option is incompatible
+with the @option{seal} option (requires at least Linux 4.16).
+
+Please refer to @option{memory-backend-file} for a description of the
+other options.
+
 @item -object rng-random,id=@var{id},filename=@var{/dev/random}
 
 Creates a random number generator backend which obtains entropy from