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Thu, 9 Nov 2023 09:05:25 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CAA98492BE7; Thu, 9 Nov 2023 09:05:24 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id B9AAD21E6A1F; Thu, 9 Nov 2023 10:05:23 +0100 (CET) From: Markus Armbruster To: =?utf-8?Q?C=C3=A9dric?= Le Goater Cc: Markus Armbruster , Zhenzhong Duan , qemu-devel@nongnu.org, alex.williamson@redhat.com, jgg@nvidia.com, nicolinc@nvidia.com, joao.m.martins@oracle.com, eric.auger@redhat.com, peterx@redhat.com, jasowang@redhat.com, kevin.tian@intel.com, yi.l.liu@intel.com, yi.y.sun@intel.com, chao.p.peng@intel.com, Paolo Bonzini , Eric Blake , Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Eduardo Habkost , Thomas Huth Subject: Re: [PATCH v4 26/41] backends/iommufd: Introduce the iommufd object References: <20231102071302.1818071-1-zhenzhong.duan@intel.com> <20231102071302.1818071-27-zhenzhong.duan@intel.com> <87r0l0dc9q.fsf@pond.sub.org> <87zfzoa65e.fsf@pond.sub.org> <20de5dde-2a1a-4d20-bafc-b63a8015fae7@redhat.com> Date: Thu, 09 Nov 2023 10:05:23 +0100 In-Reply-To: <20de5dde-2a1a-4d20-bafc-b63a8015fae7@redhat.com> (=?utf-8?Q?=22C=C3=A9dric?= Le Goater"'s message of "Wed, 8 Nov 2023 14:48:55 +0100") Message-ID: <871qcz70vg.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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, T_SCC_BODY_TEXT_LINE=-0.01 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 C=C3=A9dric Le Goater writes: > On 11/8/23 11:30, Markus Armbruster wrote: >> C=C3=A9dric Le Goater writes: >>=20 >>> Hello Markus, >>> >>> On 11/8/23 06:50, Markus Armbruster wrote: >>>> C=C3=A9dric Le Goater writes: >>>> >>>>> On 11/2/23 08:12, Zhenzhong Duan wrote: >>>>>> From: Eric Auger >>>>>> 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. >>>>>> The CONFIG_IOMMUFD option must be set to compile this new object. >>>>>> Suggested-by: Alex Williamson >>>>>> Signed-off-by: Eric Auger >>>>>> Signed-off-by: Yi Liu >>>>>> Signed-off-by: Zhenzhong Duan >>>>>> --- >>>>>> v4: add CONFIG_IOMMUFD check, document default case >>>>>> MAINTAINERS | 7 ++ >>>>>> qapi/qom.json | 22 ++++ >>>>>> include/sysemu/iommufd.h | 46 +++++++ >>>>>> backends/iommufd-stub.c | 59 +++++++++ >>>>>> backends/iommufd.c | 257 +++++++++++++++++++++++++++++++++= ++++++ >>>>>> backends/Kconfig | 4 + >>>>>> backends/meson.build | 5 + >>>>>> backends/trace-events | 12 ++ >>>>>> qemu-options.hx | 13 ++ >>>>>> 9 files changed, 425 insertions(+) >>>>>> create mode 100644 include/sysemu/iommufd.h >>>>>> create mode 100644 backends/iommufd-stub.c >>>>>> create mode 100644 backends/iommufd.c >>>>>> diff --git a/MAINTAINERS b/MAINTAINERS >>>>>> index cd8d6b140f..6f35159255 100644 >>>>>> --- a/MAINTAINERS >>>>>> +++ b/MAINTAINERS >>>>>> @@ -2135,6 +2135,13 @@ F: hw/vfio/ap.c >>>>>> F: docs/system/s390x/vfio-ap.rst >>>>>> L: qemu-s390x@nongnu.org >>>>>> +iommufd >>>>>> +M: Yi Liu >>>>>> +M: Eric Auger >>>>>> +S: Supported >>>>>> +F: backends/iommufd.c >>>>>> +F: include/sysemu/iommufd.h >>>>>> + >>>>>> vhost >>>>>> M: Michael S. Tsirkin >>>>>> S: Supported >>>>>> diff --git a/qapi/qom.json b/qapi/qom.json >>>>>> index c53ef978ff..27300add48 100644 >>>>>> --- a/qapi/qom.json >>>>>> +++ b/qapi/qom.json >>>>>> @@ -794,6 +794,24 @@ >>>>>> { '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: 8.2 >>>>>> +## >>>>>> +{ 'struct': 'IOMMUFDProperties', >>>>>> + 'data': { '*fd': 'str' }, >>>>>> + 'if': 'CONFIG_IOMMUFD' } >>>>> >>>>> >>>>> Activating or not IOMMUFD on a platform is a configuration choice >>>>> and it is not a dependency on an external resource. I would make >>>>> things simpler and drop all the #ifdef in the documentation files. >>>> >>>> What exactly are you proposing? >>> >>> I would like to simplify the configuration part of this new IOMMUFD >>> feature and avoid a ./configure option to enable/disable the feature >>> since it has no external dependencies and can be compiled on all >>> platforms. >>> >>> However, we know that it only makes sense to have the IOMMUFD backend >>> on platforms s390x, aarch64, x86_64. So I am proposing as an improvement >>> to enable IOMMUFD only on these platforms with this addition : >>> >>> imply IOMMUFD >>> >>> to hw/{i386,s390x,arm}/Kconfig files. >>> >>> This gives us the possibility to compile out the feature downstream >>> if something goes wrong, using the files under : configs/devices/. >>=20 >> Shouldn't we then compile out the relevant parts of the QAPI schema, >> too? > > Is it possible with Kconfig options ? See below. >>> Given that the IOMMUFD feature doesn't have any external dependencies >>> and that the IOMMUFD backend object is common to all platforms, I am >>> also proposing to remove all the CONFIG_IOMMUFD define usage in the >>> documentation file "qemu-options.hx" and the schema file "qapi/qom.json= ". >>=20 >> Any CONFIG_IOMMUFD left elsewhere? > > There are. To expose or not vfio properties. Stuff like : > > ifdef CONFIG_IOMMUFD > DEFINE_PROP_LINK("iommufd", VFIOPCIDevice, vbasedev.iommufd, > TYPE_IOMMUFD_BACKEND, IOMMUFDBackend *), > #endif > DEFINE_PROP_END_OF_LIST(), > > and > > #ifdef CONFIG_IOMMUFD > object_class_property_add_str(klass, "fd", NULL, vfio_pci_set_fd); > #endif > > >>>> The use of 'if': 'CONFIG_IOMMUFD' in the QAPI schema enables >>>> introspection with query-qmp-schema: when ObjectType @iommufd exists, >>>> QEMU supports creating the object. Or am I confused? >>> >>> Object iommufd should always exist since it is common to all. >>> >>> Is that acceptable ? >>=20 >> Perhaps the question to ask is whether a management application needs to >> know whether this version of QEMU supports iommufd objects. If yes, >> then query-qmp-schema is an obvious way to find out.=20=20 > > Thanks for reminding me of this possibility. In that case, we should > indeed avoid returning iommufd support when !CONFIG_IOMMUFD. > > Can it be implemented in qapi/qom.json with Kconfig options ? The only tool we have for configuring the schema is the 'if' conditional. 'if': 'CONFIG_IOMMUFD' compiles to #if defined(CONFIG_IOMMUFD) ... #endif. Your use of #ifdef CONFIG_IOMMUFD above suggests this is fine here. Symbols that are only defined in target-dependent compiles (see exec/poison.h) can only be used in target-dependent schema modules, i.e. the *-target.json. >> What could go >> wrong when this returns "supported" when it actually isn't? >=20=20=20 > The management layer would build an invalid QEMU command line and > QEMU would return "invalid object type: iommufd" > > Thanks, > > C.