Messages in this thread | | | Date | Wed, 6 Apr 2022 17:51:03 +0800 | Subject | Re: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown() | From | Lu Baolu <> |
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On 2022/4/5 22:10, Jason Gunthorpe wrote: > On Tue, Apr 05, 2022 at 02:12:42PM +0800, Lu Baolu wrote: >> On 2022/4/5 1:24, Jason Gunthorpe wrote: >>> On Mon, Apr 04, 2022 at 01:43:49PM +0800, Lu Baolu wrote: >>>> On 2022/3/30 19:58, Jason Gunthorpe wrote: >>>>>>> Testing the group size is inherently the wrong test to make. >>>>>> What is your suggestion then? >>>>> Add a flag to the group that positively indicates the group can never >>>>> have more than one member, even after hot plug. eg because it is >>>>> impossible due to ACS, or lack of bridges, and so on. >>>> >>>> The check method seems to be bus specific. For platform devices, perhaps >>>> this kind of information should be retrieved from firmware interfaces >>>> like APCI or DT. >>>> >>>> From this point of view, would it be simpler and more reasonable for the >>>> device driver to do such check? After all, it is the device driver that >>>> decides whether to provide SVA services to the application via uacce. >>> >>> The check has to do with the interconnect, not the device - I don't >>> see how a device driver would know any better. >> >> I'm worried about how to support this group flag for devices that are >> not connected to the system through PCI buses. If IOMMU can support >> sva_bind() only when this flag is set, the SVA on many devices cannot >> be supported. Or this flag is always set for non PCI devices by >> default? > > IHMO it is not so different from how we determine if ACS like > functionality is supported on non-PCI. It is really just a more narrow > application of the existing ACS idea. > > For instance it may be that if the iommu_group came from DT we can > assume it is static and then singleton can know ACS is reliable.
Okay, let me head this direction.
Best regards, baolu
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