Cédric Le Goater <c...@redhat.com> writes:
> Hello Markus,
>
> On 11/8/23 06:50, Markus Armbruster wrote:
>> Cédric Le Goater <c...@redhat.com> writes:
>>
>>> On 11/2/23 08:12, Zhenzhong Duan wrote:
>>>> From: Eric Auger <eric.au...@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.
>>>> The CONFIG_IOMMUFD option must be set to compile this new object.
>>>> Suggested-by: Alex Williamson <alex.william...@redhat.com>
>>>> Signed-off-by: Eric Auger <eric.au...@redhat.com>
>>>> Signed-off-by: Yi Liu <yi.l....@intel.com>
>>>> Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
>>>> ---
>>>> 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-s3...@nongnu.org
>>>> +iommufd
>>>> +M: Yi Liu <yi.l....@intel.com>
>>>> +M: Eric Auger <eric.au...@redhat.com>
>>>> +S: Supported
>>>> +F: backends/iommufd.c
>>>> +F: include/sysemu/iommufd.h
>>>> +
>>>> vhost
>>>> M: Michael S. Tsirkin <m...@redhat.com>
>>>> 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/.
Shouldn't we then compile out the relevant parts of the QAPI schema,
too?
> 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".
Any CONFIG_IOMMUFD left elsewhere?
>> 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 ?
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. What could go
wrong when this returns "supported" when it actually isn't?
