Messages in this thread | | | Date | Mon, 19 Jun 2023 11:20:58 +0100 | Subject | Re: Question about reserved_regions w/ Intel IOMMU | From | Robin Murphy <> |
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On 2023-06-16 19:59, Jason Gunthorpe wrote: > On Fri, Jun 16, 2023 at 05:34:53PM +0100, Robin Murphy wrote: >> >> If the system has working ACS configured correctly, then this issue should >> be moot; > > Yes > >> if it doesn't, then a VFIO user is going to get a whole group of >> peer devices if they're getting anything at all, so it doesn't seem entirely >> unreasonable to leave it up to them to check that all those devices' >> resources play well with their expected memory map. > > I think the kernel should be helping here.. 'go figure it out from > lspci' is a very convoluted and obscure uAPI, and I don't see things > like DPDK actually doing that. > > IMHO the uAPI expectation is that the kernel informs userspace what > the usable IOVA is, if bridge windows and lack of ACS are rendering > address space unusable then VFIO/iommufd should return it as excluded > as well. > > If we are going to do that then all UNAMANGED domain users should > follow the same logic. > > We probably have avoided bug reports because of how rare it would be > to see a switch and an UNMANAGED domain using scenario together - > especially with ACS turned off. > > So it is really narrow niche.. Obscure enough I'm not going to make > patches :)
The main thing is that we've already been round this once before; we tried it 6 years ago and then reverted it a year later for causing more problems than it solved:
https://lkml.org/lkml/2018/3/2/760
Thanks, Robin.
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