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[87.12.25.33]) by smtp.gmail.com with ESMTPSA id g9-20020a05600c4ec900b00414659ba8c2sm11794460wmq.37.2024.03.26.06.40.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 Mar 2024 06:40:24 -0700 (PDT) From: Stefano Garzarella To: qemu-devel@nongnu.org Cc: "Michael S. Tsirkin" , gmaglione@redhat.com, Eric Blake , Eduardo Habkost , Hanna Reitz , stefanha@redhat.com, Coiby Xu , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Igor Mammedov , Jason Wang , Raphael Norwitz , slp@redhat.com, =?utf-8?q?Marc-And?= =?utf-8?q?r=C3=A9_Lureau?= , David Hildenbrand , Laurent Vivier , Markus Armbruster , Thomas Huth , Brad Smith , qemu-block@nongnu.org, Paolo Bonzini , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , Kevin Wolf , Stefano Garzarella Subject: [PATCH for-9.1 v2 09/11] hostmem: add a new memory backend based on POSIX shm_open() Date: Tue, 26 Mar 2024 14:39:34 +0100 Message-ID: <20240326133936.125332-10-sgarzare@redhat.com> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240326133936.125332-1-sgarzare@redhat.com> References: <20240326133936.125332-1-sgarzare@redhat.com> MIME-Version: 1.0 Content-type: text/plain Received-SPF: pass client-ip=170.10.133.124; envelope-from=sgarzare@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.088, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org shm_open() creates and opens a new POSIX shared memory object. A POSIX shared memory object allows creating memory backend with an associated file descriptor that can be shared with external processes (e.g. vhost-user). The new `memory-backend-shm` can be used as an alternative when `memory-backend-memfd` is not available (Linux only), since shm_open() should be provided by any POSIX-compliant operating system. Signed-off-by: Stefano Garzarella --- docs/system/devices/vhost-user.rst | 5 +- qapi/qom.json | 17 +++++ backends/hostmem-shm.c | 118 +++++++++++++++++++++++++++++ backends/meson.build | 1 + qemu-options.hx | 10 +++ 5 files changed, 149 insertions(+), 2 deletions(-) create mode 100644 backends/hostmem-shm.c diff --git a/docs/system/devices/vhost-user.rst b/docs/system/devices/vhost-user.rst index 9b2da106ce..35259d8ec7 100644 --- a/docs/system/devices/vhost-user.rst +++ b/docs/system/devices/vhost-user.rst @@ -98,8 +98,9 @@ Shared memory object In order for the daemon to access the VirtIO queues to process the requests it needs access to the guest's address space. This is -achieved via the ``memory-backend-file`` or ``memory-backend-memfd`` -objects. A reference to a file-descriptor which can access this object +achieved via the ``memory-backend-file``, ``memory-backend-memfd``, or +``memory-backend-shm`` objects. +A reference to a file-descriptor which can access this object will be passed via the socket as part of the protocol negotiation. Currently the shared memory object needs to match the size of the main diff --git a/qapi/qom.json b/qapi/qom.json index baae3a183f..88136b861d 100644 --- a/qapi/qom.json +++ b/qapi/qom.json @@ -720,6 +720,19 @@ '*hugetlbsize': 'size', '*seal': 'bool' } } +## +# @MemoryBackendShmProperties: +# +# Properties for memory-backend-shm objects. +# +# The @share boolean option is true by default with shm. +# +# Since: 9.1 +## +{ 'struct': 'MemoryBackendShmProperties', + 'base': 'MemoryBackendProperties', + 'data': { } } + ## # @MemoryBackendEpcProperties: # @@ -976,6 +989,8 @@ { 'name': 'memory-backend-memfd', 'if': 'CONFIG_LINUX' }, 'memory-backend-ram', + { 'name': 'memory-backend-shm', + 'if': 'CONFIG_POSIX' }, 'pef-guest', { 'name': 'pr-manager-helper', 'if': 'CONFIG_LINUX' }, @@ -1047,6 +1062,8 @@ 'memory-backend-memfd': { 'type': 'MemoryBackendMemfdProperties', 'if': 'CONFIG_LINUX' }, 'memory-backend-ram': 'MemoryBackendProperties', + 'memory-backend-shm': { 'type': 'MemoryBackendShmProperties', + 'if': 'CONFIG_POSIX' }, 'pr-manager-helper': { 'type': 'PrManagerHelperProperties', 'if': 'CONFIG_LINUX' }, 'qtest': 'QtestProperties', diff --git a/backends/hostmem-shm.c b/backends/hostmem-shm.c new file mode 100644 index 0000000000..7595204d29 --- /dev/null +++ b/backends/hostmem-shm.c @@ -0,0 +1,118 @@ +/* + * QEMU host POSIX shared memory object backend + * + * Copyright (C) 2024 Red Hat Inc + * + * Authors: + * Stefano Garzarella + * + * 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 "sysemu/hostmem.h" +#include "qapi/error.h" + +#define TYPE_MEMORY_BACKEND_SHM "memory-backend-shm" + +OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendShm, MEMORY_BACKEND_SHM) + +struct HostMemoryBackendShm { + HostMemoryBackend parent_obj; +}; + +static bool +shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) +{ + g_autoptr(GString) shm_name = g_string_new(NULL); + g_autofree char *backend_name = NULL; + uint32_t ram_flags; + int fd, oflag; + mode_t mode; + + if (!backend->size) { + error_setg(errp, "can't create backend with size 0"); + return false; + } + + /* + * Let's use `mode = 0` because we don't want other processes to open our + * memory unless we share the file descriptor with them. + */ + mode = 0; + oflag = O_RDWR | O_CREAT | O_EXCL; + backend_name = host_memory_backend_get_name(backend); + + /* + * Some operating systems allow creating anonymous POSIX shared memory + * objects (e.g. FreeBSD provides the SHM_ANON constant), but this is not + * defined by POSIX, so let's create a unique name. + * + * From Linux's shm_open(3) man-page: + * For portable use, a shared memory object should be identified + * by a name of the form /somename;" + */ + g_string_printf(shm_name, "/qemu-" FMT_pid "-shm-%s", getpid(), + backend_name); + + fd = shm_open(shm_name->str, oflag, mode); + if (fd < 0) { + error_setg_errno(errp, errno, + "failed to create POSIX shared memory"); + return false; + } + + /* + * We have the file descriptor, so we no longer need to expose the + * POSIX shared memory object. However it will remain allocated as long as + * there are file descriptors pointing to it. + */ + shm_unlink(shm_name->str); + + if (ftruncate(fd, backend->size) == -1) { + error_setg_errno(errp, errno, + "failed to resize POSIX shared memory to %" PRIu64, + backend->size); + close(fd); + return false; + } + + ram_flags = backend->share ? RAM_SHARED : 0; + ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; + + return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), + backend_name, backend->size, + ram_flags, fd, 0, errp); +} + +static void +shm_backend_instance_init(Object *obj) +{ + HostMemoryBackendShm *m = MEMORY_BACKEND_SHM(obj); + + MEMORY_BACKEND(m)->share = true; +} + +static void +shm_backend_class_init(ObjectClass *oc, void *data) +{ + HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc); + + bc->alloc = shm_backend_memory_alloc; +} + +static const TypeInfo shm_backend_info = { + .name = TYPE_MEMORY_BACKEND_SHM, + .parent = TYPE_MEMORY_BACKEND, + .instance_init = shm_backend_instance_init, + .class_init = shm_backend_class_init, + .instance_size = sizeof(HostMemoryBackendShm), +}; + +static void register_types(void) +{ + type_register_static(&shm_backend_info); +} + +type_init(register_types); diff --git a/backends/meson.build b/backends/meson.build index 8b2b111497..3867b0d363 100644 --- a/backends/meson.build +++ b/backends/meson.build @@ -13,6 +13,7 @@ system_ss.add([files( if host_os != 'windows' system_ss.add(files('rng-random.c')) system_ss.add(files('hostmem-file.c')) + system_ss.add([files('hostmem-shm.c'), rt]) endif if host_os == 'linux' system_ss.add(files('hostmem-memfd.c')) diff --git a/qemu-options.hx b/qemu-options.hx index 7fd1713fa8..70fa98ba19 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -5230,6 +5230,16 @@ SRST The ``share`` boolean option is on by default with memfd. + ``-object memory-backend-shm,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave`` + Creates a POSIX shared memory backend object, which allows + QEMU to share the memory with an external process (e.g. when + using vhost-user). + + Please refer to ``memory-backend-file`` for a description of the + options. + + The ``share`` boolean option is on by default with shm. + ``-object iommufd,id=id[,fd=fd]`` Creates an iommufd backend which allows control of DMA mapping through the ``/dev/iommu`` device.