From: Eric Auger <eric.auger@redhat.com>
Introduce an iommufd object which allows the interaction
with the host /dev/iommu device.
The /dev/iommu can have been already pre-opened outside of qemu,
in which case the fd can be passed directly along with the
iommufd object:
This allows the iommufd object to be shared accross several
subsystems (VFIO, VDPA, ...). For example, libvirt would open
the /dev/iommu once.
If no fd is passed along with the iommufd object, the /dev/iommu
is opened by the qemu code.
Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
MAINTAINERS | 8 ++
qapi/qom.json | 19 +++
include/sysemu/iommufd.h | 38 ++++++
backends/iommufd.c | 245 +++++++++++++++++++++++++++++++++++++++
backends/Kconfig | 4 +
backends/meson.build | 1 +
backends/trace-events | 10 ++
qemu-options.hx | 12 ++
8 files changed, 337 insertions(+)
create mode 100644 include/sysemu/iommufd.h
create mode 100644 backends/iommufd.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 695e0bd34fbba253d77570e5b3ef8dabe7a174b3..a5a446914a1cf505131bfe113540fd501511abb8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2167,6 +2167,14 @@ F: hw/vfio/ap.c
F: docs/system/s390x/vfio-ap.rst
L: qemu-s390x@nongnu.org
+iommufd
+M: Yi Liu <yi.l.liu@intel.com>
+M: Eric Auger <eric.auger@redhat.com>
+M: Zhenzhong Duan <zhenzhong.duan@intel.com>
+S: Supported
+F: backends/iommufd.c
+F: include/sysemu/iommufd.h
+
vhost
M: Michael S. Tsirkin <mst@redhat.com>
S: Supported
diff --git a/qapi/qom.json b/qapi/qom.json
index c53ef978ff7e6a81f8c926159fe52c0d349696ac..95516ba325e541e5eeb3e1f588474cdf63ad68a5 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -794,6 +794,23 @@
{ 'struct': 'VfioUserServerProperties',
'data': { 'socket': 'SocketAddress', 'device': 'str' } }
+##
+# @IOMMUFDProperties:
+#
+# Properties for iommufd objects.
+#
+# @fd: file descriptor name previously passed via 'getfd' command,
+# which represents a pre-opened /dev/iommu. This allows the
+# iommufd object to be shared accross several subsystems
+# (VFIO, VDPA, ...), and the file descriptor to be shared
+# with other process, e.g. DPDK. (default: QEMU opens
+# /dev/iommu by itself)
+#
+# Since: 9.0
+##
+{ 'struct': 'IOMMUFDProperties',
+ 'data': { '*fd': 'str' } }
+
##
# @RngProperties:
#
@@ -934,6 +951,7 @@
'input-barrier',
{ 'name': 'input-linux',
'if': 'CONFIG_LINUX' },
+ 'iommufd',
'iothread',
'main-loop',
{ 'name': 'memory-backend-epc',
@@ -1003,6 +1021,7 @@
'input-barrier': 'InputBarrierProperties',
'input-linux': { 'type': 'InputLinuxProperties',
'if': 'CONFIG_LINUX' },
+ 'iommufd': 'IOMMUFDProperties',
'iothread': 'IothreadProperties',
'main-loop': 'MainLoopProperties',
'memory-backend-epc': { 'type': 'MemoryBackendEpcProperties',
diff --git a/include/sysemu/iommufd.h b/include/sysemu/iommufd.h
new file mode 100644
index 0000000000000000000000000000000000000000..9c5524b0ed15ef5f81be159415bc216572a283d8
--- /dev/null
+++ b/include/sysemu/iommufd.h
@@ -0,0 +1,38 @@
+#ifndef SYSEMU_IOMMUFD_H
+#define SYSEMU_IOMMUFD_H
+
+#include "qom/object.h"
+#include "qemu/thread.h"
+#include "exec/hwaddr.h"
+#include "exec/cpu-common.h"
+
+#define TYPE_IOMMUFD_BACKEND "iommufd"
+OBJECT_DECLARE_TYPE(IOMMUFDBackend, IOMMUFDBackendClass, IOMMUFD_BACKEND)
+
+struct IOMMUFDBackendClass {
+ ObjectClass parent_class;
+};
+
+struct IOMMUFDBackend {
+ Object parent;
+
+ /*< protected >*/
+ int fd; /* /dev/iommu file descriptor */
+ bool owned; /* is the /dev/iommu opened internally */
+ QemuMutex lock;
+ uint32_t users;
+
+ /*< public >*/
+};
+
+int iommufd_backend_connect(IOMMUFDBackend *be, Error **errp);
+void iommufd_backend_disconnect(IOMMUFDBackend *be);
+
+int iommufd_backend_alloc_ioas(IOMMUFDBackend *be, uint32_t *ioas_id,
+ Error **errp);
+void iommufd_backend_free_id(IOMMUFDBackend *be, uint32_t id);
+int iommufd_backend_map_dma(IOMMUFDBackend *be, uint32_t ioas_id, hwaddr iova,
+ ram_addr_t size, void *vaddr, bool readonly);
+int iommufd_backend_unmap_dma(IOMMUFDBackend *be, uint32_t ioas_id,
+ hwaddr iova, ram_addr_t size);
+#endif
diff --git a/backends/iommufd.c b/backends/iommufd.c
new file mode 100644
index 0000000000000000000000000000000000000000..ba58a0eb0d0ba9aae625c987eb728547543dba66
--- /dev/null
+++ b/backends/iommufd.c
@@ -0,0 +1,245 @@
+/*
+ * iommufd container backend
+ *
+ * Copyright (C) 2023 Intel Corporation.
+ * Copyright Red Hat, Inc. 2023
+ *
+ * Authors: Yi Liu <yi.l.liu@intel.com>
+ * Eric Auger <eric.auger@redhat.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "sysemu/iommufd.h"
+#include "qapi/error.h"
+#include "qapi/qmp/qerror.h"
+#include "qemu/module.h"
+#include "qom/object_interfaces.h"
+#include "qemu/error-report.h"
+#include "monitor/monitor.h"
+#include "trace.h"
+#include <sys/ioctl.h>
+#include <linux/iommufd.h>
+
+static void iommufd_backend_init(Object *obj)
+{
+ IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
+
+ be->fd = -1;
+ be->users = 0;
+ be->owned = true;
+ qemu_mutex_init(&be->lock);
+}
+
+static void iommufd_backend_finalize(Object *obj)
+{
+ IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
+
+ if (be->owned) {
+ close(be->fd);
+ be->fd = -1;
+ }
+}
+
+static void iommufd_backend_set_fd(Object *obj, const char *str, Error **errp)
+{
+ IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
+ int fd = -1;
+
+ fd = monitor_fd_param(monitor_cur(), str, errp);
+ if (fd == -1) {
+ error_prepend(errp, "Could not parse remote object fd %s:", str);
+ return;
+ }
+ qemu_mutex_lock(&be->lock);
+ be->fd = fd;
+ be->owned = false;
+ qemu_mutex_unlock(&be->lock);
+ trace_iommu_backend_set_fd(be->fd);
+}
+
+static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
+{
+ IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
+
+ return !be->users;
+}
+
+static void iommufd_backend_class_init(ObjectClass *oc, void *data)
+{
+ UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+
+ ucc->can_be_deleted = iommufd_backend_can_be_deleted;
+
+ object_class_property_add_str(oc, "fd", NULL, iommufd_backend_set_fd);
+}
+
+int iommufd_backend_connect(IOMMUFDBackend *be, Error **errp)
+{
+ int fd, ret = 0;
+
+ qemu_mutex_lock(&be->lock);
+ if (be->users == UINT32_MAX) {
+ error_setg(errp, "too many connections");
+ ret = -E2BIG;
+ goto out;
+ }
+ if (be->owned && !be->users) {
+ fd = qemu_open_old("/dev/iommu", O_RDWR);
+ if (fd < 0) {
+ error_setg_errno(errp, errno, "/dev/iommu opening failed");
+ ret = fd;
+ goto out;
+ }
+ be->fd = fd;
+ }
+ be->users++;
+out:
+ trace_iommufd_backend_connect(be->fd, be->owned,
+ be->users, ret);
+ qemu_mutex_unlock(&be->lock);
+ return ret;
+}
+
+void iommufd_backend_disconnect(IOMMUFDBackend *be)
+{
+ qemu_mutex_lock(&be->lock);
+ if (!be->users) {
+ goto out;
+ }
+ be->users--;
+ if (!be->users && be->owned) {
+ close(be->fd);
+ be->fd = -1;
+ }
+out:
+ trace_iommufd_backend_disconnect(be->fd, be->users);
+ qemu_mutex_unlock(&be->lock);
+}
+
+int iommufd_backend_alloc_ioas(IOMMUFDBackend *be, uint32_t *ioas_id,
+ Error **errp)
+{
+ int ret, fd = be->fd;
+ struct iommu_ioas_alloc alloc_data = {
+ .size = sizeof(alloc_data),
+ .flags = 0,
+ };
+
+ ret = ioctl(fd, IOMMU_IOAS_ALLOC, &alloc_data);
+ if (ret) {
+ error_setg_errno(errp, errno, "Failed to allocate ioas");
+ return ret;
+ }
+
+ *ioas_id = alloc_data.out_ioas_id;
+ trace_iommufd_backend_alloc_ioas(fd, *ioas_id, ret);
+
+ return ret;
+}
+
+void iommufd_backend_free_id(IOMMUFDBackend *be, uint32_t id)
+{
+ int ret, fd = be->fd;
+ struct iommu_destroy des = {
+ .size = sizeof(des),
+ .id = id,
+ };
+
+ ret = ioctl(fd, IOMMU_DESTROY, &des);
+ trace_iommufd_backend_free_id(fd, id, ret);
+ if (ret) {
+ error_report("Failed to free id: %u %m", id);
+ }
+}
+
+int iommufd_backend_map_dma(IOMMUFDBackend *be, uint32_t ioas_id, hwaddr iova,
+ ram_addr_t size, void *vaddr, bool readonly)
+{
+ int ret, fd = be->fd;
+ struct iommu_ioas_map map = {
+ .size = sizeof(map),
+ .flags = IOMMU_IOAS_MAP_READABLE |
+ IOMMU_IOAS_MAP_FIXED_IOVA,
+ .ioas_id = ioas_id,
+ .__reserved = 0,
+ .user_va = (uintptr_t)vaddr,
+ .iova = iova,
+ .length = size,
+ };
+
+ if (!readonly) {
+ map.flags |= IOMMU_IOAS_MAP_WRITEABLE;
+ }
+
+ ret = ioctl(fd, IOMMU_IOAS_MAP, &map);
+ trace_iommufd_backend_map_dma(fd, ioas_id, iova, size,
+ vaddr, readonly, ret);
+ if (ret) {
+ ret = -errno;
+
+ /* TODO: Not support mapping hardware PCI BAR region for now. */
+ if (errno == EFAULT) {
+ warn_report("IOMMU_IOAS_MAP failed: %m, PCI BAR?");
+ } else {
+ error_report("IOMMU_IOAS_MAP failed: %m");
+ }
+ }
+ return ret;
+}
+
+int iommufd_backend_unmap_dma(IOMMUFDBackend *be, uint32_t ioas_id,
+ hwaddr iova, ram_addr_t size)
+{
+ int ret, fd = be->fd;
+ struct iommu_ioas_unmap unmap = {
+ .size = sizeof(unmap),
+ .ioas_id = ioas_id,
+ .iova = iova,
+ .length = size,
+ };
+
+ ret = ioctl(fd, IOMMU_IOAS_UNMAP, &unmap);
+ /*
+ * IOMMUFD takes mapping as some kind of object, unmapping
+ * nonexistent mapping is treated as deleting a nonexistent
+ * object and return ENOENT. This is different from legacy
+ * backend which allows it. vIOMMU may trigger a lot of
+ * redundant unmapping, to avoid flush the log, treat them
+ * as succeess for IOMMUFD just like legacy backend.
+ */
+ if (ret && errno == ENOENT) {
+ trace_iommufd_backend_unmap_dma_non_exist(fd, ioas_id, iova, size, ret);
+ ret = 0;
+ } else {
+ trace_iommufd_backend_unmap_dma(fd, ioas_id, iova, size, ret);
+ }
+
+ if (ret) {
+ ret = -errno;
+ error_report("IOMMU_IOAS_UNMAP failed: %m");
+ }
+ return ret;
+}
+
+static const TypeInfo iommufd_backend_info = {
+ .name = TYPE_IOMMUFD_BACKEND,
+ .parent = TYPE_OBJECT,
+ .instance_size = sizeof(IOMMUFDBackend),
+ .instance_init = iommufd_backend_init,
+ .instance_finalize = iommufd_backend_finalize,
+ .class_size = sizeof(IOMMUFDBackendClass),
+ .class_init = iommufd_backend_class_init,
+ .interfaces = (InterfaceInfo[]) {
+ { TYPE_USER_CREATABLE },
+ { }
+ }
+};
+
+static void register_types(void)
+{
+ type_register_static(&iommufd_backend_info);
+}
+
+type_init(register_types);
diff --git a/backends/Kconfig b/backends/Kconfig
index f35abc16092808b1fe5b033a346908e2d66bff0b..2cb23f62fa1526cedafedcc99a032e098075b846 100644
--- a/backends/Kconfig
+++ b/backends/Kconfig
@@ -1 +1,5 @@
source tpm/Kconfig
+
+config IOMMUFD
+ bool
+ depends on VFIO
diff --git a/backends/meson.build b/backends/meson.build
index 914c7c4afb905cfe710ad23dd1ee42907f6d1679..9a5cea480d172d50a641e4d9179093e8155f2db1 100644
--- a/backends/meson.build
+++ b/backends/meson.build
@@ -20,6 +20,7 @@ if have_vhost_user
system_ss.add(when: 'CONFIG_VIRTIO', if_true: files('vhost-user.c'))
endif
system_ss.add(when: 'CONFIG_VIRTIO_CRYPTO', if_true: files('cryptodev-vhost.c'))
+system_ss.add(when: 'CONFIG_IOMMUFD', if_true: files('iommufd.c'))
if have_vhost_user_crypto
system_ss.add(when: 'CONFIG_VIRTIO_CRYPTO', if_true: files('cryptodev-vhost-user.c'))
endif
diff --git a/backends/trace-events b/backends/trace-events
index 652eb76a5723e2053fe97338c481309c58284d6a..d45c6e31a67ed66d94787f60eb08a525cf6ff68b 100644
--- a/backends/trace-events
+++ b/backends/trace-events
@@ -5,3 +5,13 @@ dbus_vmstate_pre_save(void)
dbus_vmstate_post_load(int version_id) "version_id: %d"
dbus_vmstate_loading(const char *id) "id: %s"
dbus_vmstate_saving(const char *id) "id: %s"
+
+# iommufd.c
+iommufd_backend_connect(int fd, bool owned, uint32_t users, int ret) "fd=%d owned=%d users=%d (%d)"
+iommufd_backend_disconnect(int fd, uint32_t users) "fd=%d users=%d"
+iommu_backend_set_fd(int fd) "pre-opened /dev/iommu fd=%d"
+iommufd_backend_map_dma(int iommufd, uint32_t ioas, uint64_t iova, uint64_t size, void *vaddr, bool readonly, int ret) " iommufd=%d ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" addr=%p readonly=%d (%d)"
+iommufd_backend_unmap_dma_non_exist(int iommufd, uint32_t ioas, uint64_t iova, uint64_t size, int ret) " Unmap nonexistent mapping: iommufd=%d ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" (%d)"
+iommufd_backend_unmap_dma(int iommufd, uint32_t ioas, uint64_t iova, uint64_t size, int ret) " iommufd=%d ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" (%d)"
+iommufd_backend_alloc_ioas(int iommufd, uint32_t ioas, int ret) " iommufd=%d ioas=%d (%d)"
+iommufd_backend_free_id(int iommufd, uint32_t id, int ret) " iommufd=%d id=%d (%d)"
diff --git a/qemu-options.hx b/qemu-options.hx
index 42fd09e4de96e962cd5873c49501f6e1dbb5e346..5fe8ea57d2d2f9390a976ef2fefe86463e888bb1 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -5224,6 +5224,18 @@ SRST
The ``share`` boolean option is on by default with memfd.
+ ``-object iommufd,id=id[,fd=fd]``
+ Creates an iommufd backend which allows control of DMA mapping
+ through the ``/dev/iommu`` device.
+
+ The ``id`` parameter is a unique ID which frontends (such as
+ vfio-pci of vdpa) will use to connect with the iommufd backend.
+
+ The ``fd`` parameter is an optional pre-opened file descriptor
+ resulting from ``/dev/iommu`` opening. Usually the iommufd is shared
+ across all subsystems, bringing the benefit of centralized
+ reference counting.
+
``-object rng-builtin,id=id``
Creates a random number generator backend which obtains entropy
from QEMU builtin functions. The ``id`` parameter is a unique ID
--
2.43.0
[ ... ]
> +static void iommufd_backend_init(Object *obj)
> +{
> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
> +
> + be->fd = -1;
> + be->users = 0;
> + be->owned = true;
> + qemu_mutex_init(&be->lock);> +}
> +
> +static void iommufd_backend_finalize(Object *obj)
> +{
> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
> +
> + if (be->owned) {
> + close(be->fd);
> + be->fd = -1;
> + }
> +}
> +
> +static void iommufd_backend_set_fd(Object *obj, const char *str, Error **errp)
> +{
> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
> + int fd = -1;
> +
> + fd = monitor_fd_param(monitor_cur(), str, errp);
> + if (fd == -1) {
> + error_prepend(errp, "Could not parse remote object fd %s:", str);
> + return;
> + }
> + qemu_mutex_lock(&be->lock);
> + be->fd = fd;
> + be->owned = false;
> + qemu_mutex_unlock(&be->lock);
> + trace_iommu_backend_set_fd(be->fd);
> +}
> +
> +static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
> +{
> + IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
> +
> + return !be->users;
Coverity CID 1531549 reports a concurrent data access violation because
be->users is being accessed without holding the mutex.
I wonder how useful is this mutex anyhow, since the code paths should
be protected by the BQL lock. If you agree, I will send an update to
simply drop be->lock and solve this report.
Thanks,
C.
> +}
> +
> +static void iommufd_backend_class_init(ObjectClass *oc, void *data)
> +{
> + UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
> +
> + ucc->can_be_deleted = iommufd_backend_can_be_deleted;
> +
> + object_class_property_add_str(oc, "fd", NULL, iommufd_backend_set_fd);
> +}
> +
> +int iommufd_backend_connect(IOMMUFDBackend *be, Error **errp)
> +{
> + int fd, ret = 0;
> +
> + qemu_mutex_lock(&be->lock);
> + if (be->users == UINT32_MAX) {
> + error_setg(errp, "too many connections");
> + ret = -E2BIG;
> + goto out;
> + }
> + if (be->owned && !be->users) {
> + fd = qemu_open_old("/dev/iommu", O_RDWR);
> + if (fd < 0) {
> + error_setg_errno(errp, errno, "/dev/iommu opening failed");
> + ret = fd;
> + goto out;
> + }
> + be->fd = fd;
> + }
> + be->users++;
> +out:
> + trace_iommufd_backend_connect(be->fd, be->owned,
> + be->users, ret);
> + qemu_mutex_unlock(&be->lock);
> + return ret;
> +}
> +
> +void iommufd_backend_disconnect(IOMMUFDBackend *be)
> +{
> + qemu_mutex_lock(&be->lock);
> + if (!be->users) {
> + goto out;
> + }
> + be->users--;
> + if (!be->users && be->owned) {
> + close(be->fd);
> + be->fd = -1;
> + }
> +out:
> + trace_iommufd_backend_disconnect(be->fd, be->users);
> + qemu_mutex_unlock(&be->lock);
> +}
> +
> +int iommufd_backend_alloc_ioas(IOMMUFDBackend *be, uint32_t *ioas_id,
> + Error **errp)
> +{
> + int ret, fd = be->fd;
> + struct iommu_ioas_alloc alloc_data = {
> + .size = sizeof(alloc_data),
> + .flags = 0,
> + };
> +
> + ret = ioctl(fd, IOMMU_IOAS_ALLOC, &alloc_data);
> + if (ret) {
> + error_setg_errno(errp, errno, "Failed to allocate ioas");
> + return ret;
> + }
> +
> + *ioas_id = alloc_data.out_ioas_id;
> + trace_iommufd_backend_alloc_ioas(fd, *ioas_id, ret);
> +
> + return ret;
> +}
> +
> +void iommufd_backend_free_id(IOMMUFDBackend *be, uint32_t id)
> +{
> + int ret, fd = be->fd;
> + struct iommu_destroy des = {
> + .size = sizeof(des),
> + .id = id,
> + };
> +
> + ret = ioctl(fd, IOMMU_DESTROY, &des);
> + trace_iommufd_backend_free_id(fd, id, ret);
> + if (ret) {
> + error_report("Failed to free id: %u %m", id);
> + }
> +}
> +
> +int iommufd_backend_map_dma(IOMMUFDBackend *be, uint32_t ioas_id, hwaddr iova,
> + ram_addr_t size, void *vaddr, bool readonly)
> +{
> + int ret, fd = be->fd;
> + struct iommu_ioas_map map = {
> + .size = sizeof(map),
> + .flags = IOMMU_IOAS_MAP_READABLE |
> + IOMMU_IOAS_MAP_FIXED_IOVA,
> + .ioas_id = ioas_id,
> + .__reserved = 0,
> + .user_va = (uintptr_t)vaddr,
> + .iova = iova,
> + .length = size,
> + };
> +
> + if (!readonly) {
> + map.flags |= IOMMU_IOAS_MAP_WRITEABLE;
> + }
> +
> + ret = ioctl(fd, IOMMU_IOAS_MAP, &map);
> + trace_iommufd_backend_map_dma(fd, ioas_id, iova, size,
> + vaddr, readonly, ret);
> + if (ret) {
> + ret = -errno;
> +
> + /* TODO: Not support mapping hardware PCI BAR region for now. */
> + if (errno == EFAULT) {
> + warn_report("IOMMU_IOAS_MAP failed: %m, PCI BAR?");
> + } else {
> + error_report("IOMMU_IOAS_MAP failed: %m");
> + }
> + }
> + return ret;
> +}
> +
> +int iommufd_backend_unmap_dma(IOMMUFDBackend *be, uint32_t ioas_id,
> + hwaddr iova, ram_addr_t size)
> +{
> + int ret, fd = be->fd;
> + struct iommu_ioas_unmap unmap = {
> + .size = sizeof(unmap),
> + .ioas_id = ioas_id,
> + .iova = iova,
> + .length = size,
> + };
> +
> + ret = ioctl(fd, IOMMU_IOAS_UNMAP, &unmap);
> + /*
> + * IOMMUFD takes mapping as some kind of object, unmapping
> + * nonexistent mapping is treated as deleting a nonexistent
> + * object and return ENOENT. This is different from legacy
> + * backend which allows it. vIOMMU may trigger a lot of
> + * redundant unmapping, to avoid flush the log, treat them
> + * as succeess for IOMMUFD just like legacy backend.
> + */
> + if (ret && errno == ENOENT) {
> + trace_iommufd_backend_unmap_dma_non_exist(fd, ioas_id, iova, size, ret);
> + ret = 0;
> + } else {
> + trace_iommufd_backend_unmap_dma(fd, ioas_id, iova, size, ret);
> + }
> +
> + if (ret) {
> + ret = -errno;
> + error_report("IOMMU_IOAS_UNMAP failed: %m");
> + }
> + return ret;
> +}
> +
> +static const TypeInfo iommufd_backend_info = {
> + .name = TYPE_IOMMUFD_BACKEND,
> + .parent = TYPE_OBJECT,
> + .instance_size = sizeof(IOMMUFDBackend),
> + .instance_init = iommufd_backend_init,
> + .instance_finalize = iommufd_backend_finalize,
> + .class_size = sizeof(IOMMUFDBackendClass),
> + .class_init = iommufd_backend_class_init,
> + .interfaces = (InterfaceInfo[]) {
> + { TYPE_USER_CREATABLE },
> + { }
> + }
> +};
> +
> +static void register_types(void)
> +{
> + type_register_static(&iommufd_backend_info);
> +}
> +
> +type_init(register_types);
> diff --git a/backends/Kconfig b/backends/Kconfig
> index f35abc16092808b1fe5b033a346908e2d66bff0b..2cb23f62fa1526cedafedcc99a032e098075b846 100644
> --- a/backends/Kconfig
> +++ b/backends/Kconfig
> @@ -1 +1,5 @@
> source tpm/Kconfig
> +
> +config IOMMUFD
> + bool
> + depends on VFIO
> diff --git a/backends/meson.build b/backends/meson.build
> index 914c7c4afb905cfe710ad23dd1ee42907f6d1679..9a5cea480d172d50a641e4d9179093e8155f2db1 100644
> --- a/backends/meson.build
> +++ b/backends/meson.build
> @@ -20,6 +20,7 @@ if have_vhost_user
> system_ss.add(when: 'CONFIG_VIRTIO', if_true: files('vhost-user.c'))
> endif
> system_ss.add(when: 'CONFIG_VIRTIO_CRYPTO', if_true: files('cryptodev-vhost.c'))
> +system_ss.add(when: 'CONFIG_IOMMUFD', if_true: files('iommufd.c'))
> if have_vhost_user_crypto
> system_ss.add(when: 'CONFIG_VIRTIO_CRYPTO', if_true: files('cryptodev-vhost-user.c'))
> endif
> diff --git a/backends/trace-events b/backends/trace-events
> index 652eb76a5723e2053fe97338c481309c58284d6a..d45c6e31a67ed66d94787f60eb08a525cf6ff68b 100644
> --- a/backends/trace-events
> +++ b/backends/trace-events
> @@ -5,3 +5,13 @@ dbus_vmstate_pre_save(void)
> dbus_vmstate_post_load(int version_id) "version_id: %d"
> dbus_vmstate_loading(const char *id) "id: %s"
> dbus_vmstate_saving(const char *id) "id: %s"
> +
> +# iommufd.c
> +iommufd_backend_connect(int fd, bool owned, uint32_t users, int ret) "fd=%d owned=%d users=%d (%d)"
> +iommufd_backend_disconnect(int fd, uint32_t users) "fd=%d users=%d"
> +iommu_backend_set_fd(int fd) "pre-opened /dev/iommu fd=%d"
> +iommufd_backend_map_dma(int iommufd, uint32_t ioas, uint64_t iova, uint64_t size, void *vaddr, bool readonly, int ret) " iommufd=%d ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" addr=%p readonly=%d (%d)"
> +iommufd_backend_unmap_dma_non_exist(int iommufd, uint32_t ioas, uint64_t iova, uint64_t size, int ret) " Unmap nonexistent mapping: iommufd=%d ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" (%d)"
> +iommufd_backend_unmap_dma(int iommufd, uint32_t ioas, uint64_t iova, uint64_t size, int ret) " iommufd=%d ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" (%d)"
> +iommufd_backend_alloc_ioas(int iommufd, uint32_t ioas, int ret) " iommufd=%d ioas=%d (%d)"
> +iommufd_backend_free_id(int iommufd, uint32_t id, int ret) " iommufd=%d id=%d (%d)"
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 42fd09e4de96e962cd5873c49501f6e1dbb5e346..5fe8ea57d2d2f9390a976ef2fefe86463e888bb1 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -5224,6 +5224,18 @@ SRST
>
> The ``share`` boolean option is on by default with memfd.
>
> + ``-object iommufd,id=id[,fd=fd]``
> + Creates an iommufd backend which allows control of DMA mapping
> + through the ``/dev/iommu`` device.
> +
> + The ``id`` parameter is a unique ID which frontends (such as
> + vfio-pci of vdpa) will use to connect with the iommufd backend.
> +
> + The ``fd`` parameter is an optional pre-opened file descriptor
> + resulting from ``/dev/iommu`` opening. Usually the iommufd is shared
> + across all subsystems, bringing the benefit of centralized
> + reference counting.
> +
> ``-object rng-builtin,id=id``
> Creates a random number generator backend which obtains entropy
> from QEMU builtin functions. The ``id`` parameter is a unique ID
Hi Cédric,
>-----Original Message-----
>From: Cédric Le Goater <clg@redhat.com>
>Sent: Friday, December 22, 2023 12:01 AM
>Subject: Re: [PULL 20/47] backends/iommufd: Introduce the iommufd object
>
>[ ... ]
>
>
>> +static void iommufd_backend_init(Object *obj)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>> +
>> + be->fd = -1;
>> + be->users = 0;
>> + be->owned = true;
>> + qemu_mutex_init(&be->lock);> +}
>> +
>> +static void iommufd_backend_finalize(Object *obj)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>> +
>> + if (be->owned) {
>> + close(be->fd);
>> + be->fd = -1;
>> + }
>> +}
>> +
>> +static void iommufd_backend_set_fd(Object *obj, const char *str, Error
>**errp)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>> + int fd = -1;
>> +
>> + fd = monitor_fd_param(monitor_cur(), str, errp);
>> + if (fd == -1) {
>> + error_prepend(errp, "Could not parse remote object fd %s:", str);
>> + return;
>> + }
>> + qemu_mutex_lock(&be->lock);
>> + be->fd = fd;
>> + be->owned = false;
>> + qemu_mutex_unlock(&be->lock);
>> + trace_iommu_backend_set_fd(be->fd);
>> +}
>> +
>> +static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
>> +
>> + return !be->users;
>
>Coverity CID 1531549 reports a concurrent data access violation because
>be->users is being accessed without holding the mutex.
>
>I wonder how useful is this mutex anyhow, since the code paths should
>be protected by the BQL lock. If you agree, I will send an update to
>simply drop be->lock and solve this report.
Make sense on my side, thanks for help fixing.
BRs.
Zhenzhong
Hi Cédric,
On 12/21/23 17:00, Cédric Le Goater wrote:
> [ ... ]
>
>
>> +static void iommufd_backend_init(Object *obj)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>> +
>> + be->fd = -1;
>> + be->users = 0;
>> + be->owned = true;
>> + qemu_mutex_init(&be->lock);> +}
>> +
>> +static void iommufd_backend_finalize(Object *obj)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>> +
>> + if (be->owned) {
>> + close(be->fd);
>> + be->fd = -1;
>> + }
>> +}
>> +
>> +static void iommufd_backend_set_fd(Object *obj, const char *str,
>> Error **errp)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>> + int fd = -1;
>> +
>> + fd = monitor_fd_param(monitor_cur(), str, errp);
>> + if (fd == -1) {
>> + error_prepend(errp, "Could not parse remote object fd %s:",
>> str);
>> + return;
>> + }
>> + qemu_mutex_lock(&be->lock);
>> + be->fd = fd;
>> + be->owned = false;
>> + qemu_mutex_unlock(&be->lock);
>> + trace_iommu_backend_set_fd(be->fd);
>> +}
>> +
>> +static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
>> +{
>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
>> +
>> + return !be->users;
>
> Coverity CID 1531549 reports a concurrent data access violation because
> be->users is being accessed without holding the mutex.
>
> I wonder how useful is this mutex anyhow, since the code paths should
> be protected by the BQL lock. If you agree, I will send an update to
> simply drop be->lock and solve this report.
I am not totally comfortable with the fact BQL covers the same
protection? Please can you elaborate.
Thanks
Eric
>
> Thanks,
>
> C.
>
>
>
>> +}
>> +
>> +static void iommufd_backend_class_init(ObjectClass *oc, void *data)
>> +{
>> + UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
>> +
>> + ucc->can_be_deleted = iommufd_backend_can_be_deleted;
>> +
>> + object_class_property_add_str(oc, "fd", NULL,
>> iommufd_backend_set_fd);
>> +}
>> +
>> +int iommufd_backend_connect(IOMMUFDBackend *be, Error **errp)
>> +{
>> + int fd, ret = 0;
>> +
>> + qemu_mutex_lock(&be->lock);
>> + if (be->users == UINT32_MAX) {
>> + error_setg(errp, "too many connections");
>> + ret = -E2BIG;
>> + goto out;
>> + }
>> + if (be->owned && !be->users) {
>> + fd = qemu_open_old("/dev/iommu", O_RDWR);
>> + if (fd < 0) {
>> + error_setg_errno(errp, errno, "/dev/iommu opening failed");
>> + ret = fd;
>> + goto out;
>> + }
>> + be->fd = fd;
>> + }
>> + be->users++;
>> +out:
>> + trace_iommufd_backend_connect(be->fd, be->owned,
>> + be->users, ret);
>> + qemu_mutex_unlock(&be->lock);
>> + return ret;
>> +}
>> +
>> +void iommufd_backend_disconnect(IOMMUFDBackend *be)
>> +{
>> + qemu_mutex_lock(&be->lock);
>> + if (!be->users) {
>> + goto out;
>> + }
>> + be->users--;
>> + if (!be->users && be->owned) {
>> + close(be->fd);
>> + be->fd = -1;
>> + }
>> +out:
>> + trace_iommufd_backend_disconnect(be->fd, be->users);
>> + qemu_mutex_unlock(&be->lock);
>> +}
>> +
>> +int iommufd_backend_alloc_ioas(IOMMUFDBackend *be, uint32_t *ioas_id,
>> + Error **errp)
>> +{
>> + int ret, fd = be->fd;
>> + struct iommu_ioas_alloc alloc_data = {
>> + .size = sizeof(alloc_data),
>> + .flags = 0,
>> + };
>> +
>> + ret = ioctl(fd, IOMMU_IOAS_ALLOC, &alloc_data);
>> + if (ret) {
>> + error_setg_errno(errp, errno, "Failed to allocate ioas");
>> + return ret;
>> + }
>> +
>> + *ioas_id = alloc_data.out_ioas_id;
>> + trace_iommufd_backend_alloc_ioas(fd, *ioas_id, ret);
>> +
>> + return ret;
>> +}
>> +
>> +void iommufd_backend_free_id(IOMMUFDBackend *be, uint32_t id)
>> +{
>> + int ret, fd = be->fd;
>> + struct iommu_destroy des = {
>> + .size = sizeof(des),
>> + .id = id,
>> + };
>> +
>> + ret = ioctl(fd, IOMMU_DESTROY, &des);
>> + trace_iommufd_backend_free_id(fd, id, ret);
>> + if (ret) {
>> + error_report("Failed to free id: %u %m", id);
>> + }
>> +}
>> +
>> +int iommufd_backend_map_dma(IOMMUFDBackend *be, uint32_t ioas_id,
>> hwaddr iova,
>> + ram_addr_t size, void *vaddr, bool
>> readonly)
>> +{
>> + int ret, fd = be->fd;
>> + struct iommu_ioas_map map = {
>> + .size = sizeof(map),
>> + .flags = IOMMU_IOAS_MAP_READABLE |
>> + IOMMU_IOAS_MAP_FIXED_IOVA,
>> + .ioas_id = ioas_id,
>> + .__reserved = 0,
>> + .user_va = (uintptr_t)vaddr,
>> + .iova = iova,
>> + .length = size,
>> + };
>> +
>> + if (!readonly) {
>> + map.flags |= IOMMU_IOAS_MAP_WRITEABLE;
>> + }
>> +
>> + ret = ioctl(fd, IOMMU_IOAS_MAP, &map);
>> + trace_iommufd_backend_map_dma(fd, ioas_id, iova, size,
>> + vaddr, readonly, ret);
>> + if (ret) {
>> + ret = -errno;
>> +
>> + /* TODO: Not support mapping hardware PCI BAR region for
>> now. */
>> + if (errno == EFAULT) {
>> + warn_report("IOMMU_IOAS_MAP failed: %m, PCI BAR?");
>> + } else {
>> + error_report("IOMMU_IOAS_MAP failed: %m");
>> + }
>> + }
>> + return ret;
>> +}
>> +
>> +int iommufd_backend_unmap_dma(IOMMUFDBackend *be, uint32_t ioas_id,
>> + hwaddr iova, ram_addr_t size)
>> +{
>> + int ret, fd = be->fd;
>> + struct iommu_ioas_unmap unmap = {
>> + .size = sizeof(unmap),
>> + .ioas_id = ioas_id,
>> + .iova = iova,
>> + .length = size,
>> + };
>> +
>> + ret = ioctl(fd, IOMMU_IOAS_UNMAP, &unmap);
>> + /*
>> + * IOMMUFD takes mapping as some kind of object, unmapping
>> + * nonexistent mapping is treated as deleting a nonexistent
>> + * object and return ENOENT. This is different from legacy
>> + * backend which allows it. vIOMMU may trigger a lot of
>> + * redundant unmapping, to avoid flush the log, treat them
>> + * as succeess for IOMMUFD just like legacy backend.
>> + */
>> + if (ret && errno == ENOENT) {
>> + trace_iommufd_backend_unmap_dma_non_exist(fd, ioas_id, iova,
>> size, ret);
>> + ret = 0;
>> + } else {
>> + trace_iommufd_backend_unmap_dma(fd, ioas_id, iova, size, ret);
>> + }
>> +
>> + if (ret) {
>> + ret = -errno;
>> + error_report("IOMMU_IOAS_UNMAP failed: %m");
>> + }
>> + return ret;
>> +}
>> +
>> +static const TypeInfo iommufd_backend_info = {
>> + .name = TYPE_IOMMUFD_BACKEND,
>> + .parent = TYPE_OBJECT,
>> + .instance_size = sizeof(IOMMUFDBackend),
>> + .instance_init = iommufd_backend_init,
>> + .instance_finalize = iommufd_backend_finalize,
>> + .class_size = sizeof(IOMMUFDBackendClass),
>> + .class_init = iommufd_backend_class_init,
>> + .interfaces = (InterfaceInfo[]) {
>> + { TYPE_USER_CREATABLE },
>> + { }
>> + }
>> +};
>> +
>> +static void register_types(void)
>> +{
>> + type_register_static(&iommufd_backend_info);
>> +}
>> +
>> +type_init(register_types);
>> diff --git a/backends/Kconfig b/backends/Kconfig
>> index
>> f35abc16092808b1fe5b033a346908e2d66bff0b..2cb23f62fa1526cedafedcc99a032e098075b846
>> 100644
>> --- a/backends/Kconfig
>> +++ b/backends/Kconfig
>> @@ -1 +1,5 @@
>> source tpm/Kconfig
>> +
>> +config IOMMUFD
>> + bool
>> + depends on VFIO
>> diff --git a/backends/meson.build b/backends/meson.build
>> index
>> 914c7c4afb905cfe710ad23dd1ee42907f6d1679..9a5cea480d172d50a641e4d9179093e8155f2db1
>> 100644
>> --- a/backends/meson.build
>> +++ b/backends/meson.build
>> @@ -20,6 +20,7 @@ if have_vhost_user
>> system_ss.add(when: 'CONFIG_VIRTIO', if_true: files('vhost-user.c'))
>> endif
>> system_ss.add(when: 'CONFIG_VIRTIO_CRYPTO', if_true:
>> files('cryptodev-vhost.c'))
>> +system_ss.add(when: 'CONFIG_IOMMUFD', if_true: files('iommufd.c'))
>> if have_vhost_user_crypto
>> system_ss.add(when: 'CONFIG_VIRTIO_CRYPTO', if_true:
>> files('cryptodev-vhost-user.c'))
>> endif
>> diff --git a/backends/trace-events b/backends/trace-events
>> index
>> 652eb76a5723e2053fe97338c481309c58284d6a..d45c6e31a67ed66d94787f60eb08a525cf6ff68b
>> 100644
>> --- a/backends/trace-events
>> +++ b/backends/trace-events
>> @@ -5,3 +5,13 @@ dbus_vmstate_pre_save(void)
>> dbus_vmstate_post_load(int version_id) "version_id: %d"
>> dbus_vmstate_loading(const char *id) "id: %s"
>> dbus_vmstate_saving(const char *id) "id: %s"
>> +
>> +# iommufd.c
>> +iommufd_backend_connect(int fd, bool owned, uint32_t users, int ret)
>> "fd=%d owned=%d users=%d (%d)"
>> +iommufd_backend_disconnect(int fd, uint32_t users) "fd=%d users=%d"
>> +iommu_backend_set_fd(int fd) "pre-opened /dev/iommu fd=%d"
>> +iommufd_backend_map_dma(int iommufd, uint32_t ioas, uint64_t iova,
>> uint64_t size, void *vaddr, bool readonly, int ret) " iommufd=%d
>> ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" addr=%p readonly=%d (%d)"
>> +iommufd_backend_unmap_dma_non_exist(int iommufd, uint32_t ioas,
>> uint64_t iova, uint64_t size, int ret) " Unmap nonexistent mapping:
>> iommufd=%d ioas=%d iova=0x%"PRIx64" size=0x%"PRIx64" (%d)"
>> +iommufd_backend_unmap_dma(int iommufd, uint32_t ioas, uint64_t iova,
>> uint64_t size, int ret) " iommufd=%d ioas=%d iova=0x%"PRIx64"
>> size=0x%"PRIx64" (%d)"
>> +iommufd_backend_alloc_ioas(int iommufd, uint32_t ioas, int ret) "
>> iommufd=%d ioas=%d (%d)"
>> +iommufd_backend_free_id(int iommufd, uint32_t id, int ret) "
>> iommufd=%d id=%d (%d)"
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index
>> 42fd09e4de96e962cd5873c49501f6e1dbb5e346..5fe8ea57d2d2f9390a976ef2fefe86463e888bb1
>> 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -5224,6 +5224,18 @@ SRST
>> The ``share`` boolean option is on by default with memfd.
>> + ``-object iommufd,id=id[,fd=fd]``
>> + Creates an iommufd backend which allows control of DMA mapping
>> + through the ``/dev/iommu`` device.
>> +
>> + The ``id`` parameter is a unique ID which frontends (such as
>> + vfio-pci of vdpa) will use to connect with the iommufd backend.
>> +
>> + The ``fd`` parameter is an optional pre-opened file descriptor
>> + resulting from ``/dev/iommu`` opening. Usually the iommufd
>> is shared
>> + across all subsystems, bringing the benefit of centralized
>> + reference counting.
>> +
>> ``-object rng-builtin,id=id``
>> Creates a random number generator backend which obtains
>> entropy
>> from QEMU builtin functions. The ``id`` parameter is a
>> unique ID
>
On 12/21/23 18:14, Eric Auger wrote:
> Hi Cédric,
>
> On 12/21/23 17:00, Cédric Le Goater wrote:
>> [ ... ]
>>
>>
>>> +static void iommufd_backend_init(Object *obj)
>>> +{
>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>> +
>>> + be->fd = -1;
>>> + be->users = 0;
>>> + be->owned = true;
>>> + qemu_mutex_init(&be->lock);> +}
>>> +
>>> +static void iommufd_backend_finalize(Object *obj)
>>> +{
>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>> +
>>> + if (be->owned) {
>>> + close(be->fd);
>>> + be->fd = -1;
>>> + }
>>> +}
>>> +
>>> +static void iommufd_backend_set_fd(Object *obj, const char *str,
>>> Error **errp)
>>> +{
>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>> + int fd = -1;
>>> +
>>> + fd = monitor_fd_param(monitor_cur(), str, errp);
>>> + if (fd == -1) {
>>> + error_prepend(errp, "Could not parse remote object fd %s:",
>>> str);
>>> + return;
>>> + }
>>> + qemu_mutex_lock(&be->lock);
>>> + be->fd = fd;
>>> + be->owned = false;
>>> + qemu_mutex_unlock(&be->lock);
>>> + trace_iommu_backend_set_fd(be->fd);
>>> +}
>>> +
>>> +static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
>>> +{
>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
>>> +
>>> + return !be->users;
>>
>> Coverity CID 1531549 reports a concurrent data access violation because
>> be->users is being accessed without holding the mutex.
>>
>> I wonder how useful is this mutex anyhow, since the code paths should
>> be protected by the BQL lock. If you agree, I will send an update to
>> simply drop be->lock and solve this report.
> I am not totally comfortable with the fact BQL covers the same
> protection? Please can you elaborate.
These routines are called when a device is created which is called
from the QEMU main thread which exits holding the BQL. It should be
fine.
Thanks,
C.
Hi Cédric,
On 12/21/23 22:23, Cédric Le Goater wrote:
> On 12/21/23 18:14, Eric Auger wrote:
>> Hi Cédric,
>>
>> On 12/21/23 17:00, Cédric Le Goater wrote:
>>> [ ... ]
>>>
>>>
>>>> +static void iommufd_backend_init(Object *obj)
>>>> +{
>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>>> +
>>>> + be->fd = -1;
>>>> + be->users = 0;
>>>> + be->owned = true;
>>>> + qemu_mutex_init(&be->lock);> +}
>>>> +
>>>> +static void iommufd_backend_finalize(Object *obj)
>>>> +{
>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>>> +
>>>> + if (be->owned) {
>>>> + close(be->fd);
>>>> + be->fd = -1;
>>>> + }
>>>> +}
>>>> +
>>>> +static void iommufd_backend_set_fd(Object *obj, const char *str,
>>>> Error **errp)
>>>> +{
>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>>> + int fd = -1;
>>>> +
>>>> + fd = monitor_fd_param(monitor_cur(), str, errp);
>>>> + if (fd == -1) {
>>>> + error_prepend(errp, "Could not parse remote object fd %s:",
>>>> str);
>>>> + return;
>>>> + }
>>>> + qemu_mutex_lock(&be->lock);
>>>> + be->fd = fd;
>>>> + be->owned = false;
>>>> + qemu_mutex_unlock(&be->lock);
>>>> + trace_iommu_backend_set_fd(be->fd);
>>>> +}
>>>> +
>>>> +static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
>>>> +{
>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
>>>> +
>>>> + return !be->users;
>>>
>>> Coverity CID 1531549 reports a concurrent data access violation because
>>> be->users is being accessed without holding the mutex.
>>>
>>> I wonder how useful is this mutex anyhow, since the code paths should
>>> be protected by the BQL lock. If you agree, I will send an update to
>>> simply drop be->lock and solve this report.
>> I am not totally comfortable with the fact BQL covers the same
>> protection? Please can you elaborate.
>
> These routines are called when a device is created which is called
> from the QEMU main thread which exits holding the BQL. It should be
> fine.
OK fine for me as well
Thanks
Eric
>
> Thanks,
>
> C.
>
>
On 12/22/23 11:09, Eric Auger wrote:
> Hi Cédric,
>
> On 12/21/23 22:23, Cédric Le Goater wrote:
>> On 12/21/23 18:14, Eric Auger wrote:
>>> Hi Cédric,
>>>
>>> On 12/21/23 17:00, Cédric Le Goater wrote:
>>>> [ ... ]
>>>>
>>>>
>>>>> +static void iommufd_backend_init(Object *obj)
>>>>> +{
>>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>>>> +
>>>>> + be->fd = -1;
>>>>> + be->users = 0;
>>>>> + be->owned = true;
>>>>> + qemu_mutex_init(&be->lock);> +}
>>>>> +
>>>>> +static void iommufd_backend_finalize(Object *obj)
>>>>> +{
>>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>>>> +
>>>>> + if (be->owned) {
>>>>> + close(be->fd);
>>>>> + be->fd = -1;
>>>>> + }
>>>>> +}
>>>>> +
>>>>> +static void iommufd_backend_set_fd(Object *obj, const char *str,
>>>>> Error **errp)
>>>>> +{
>>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(obj);
>>>>> + int fd = -1;
>>>>> +
>>>>> + fd = monitor_fd_param(monitor_cur(), str, errp);
>>>>> + if (fd == -1) {
>>>>> + error_prepend(errp, "Could not parse remote object fd %s:",
>>>>> str);
>>>>> + return;
>>>>> + }
>>>>> + qemu_mutex_lock(&be->lock);
>>>>> + be->fd = fd;
>>>>> + be->owned = false;
>>>>> + qemu_mutex_unlock(&be->lock);
>>>>> + trace_iommu_backend_set_fd(be->fd);
>>>>> +}
>>>>> +
>>>>> +static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
>>>>> +{
>>>>> + IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
>>>>> +
>>>>> + return !be->users;
>>>>
>>>> Coverity CID 1531549 reports a concurrent data access violation because
>>>> be->users is being accessed without holding the mutex.
>>>>
>>>> I wonder how useful is this mutex anyhow, since the code paths should
>>>> be protected by the BQL lock. If you agree, I will send an update to
>>>> simply drop be->lock and solve this report.
>>> I am not totally comfortable with the fact BQL covers the same
>>> protection? Please can you elaborate.
>>
>> These routines are called when a device is created which is called
>> from the QEMU main thread which exits holding the BQL. It should be
>> fine.
>
> OK fine for me as well
I pushed 2 patches on vfio-9.0 that I will send next year. Time for a
break !
Cheers,
C.
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