Messages in this thread | | | Subject | Re: [RFC] /dev/ioasid uAPI proposal | From | Lu Baolu <> | Date | Thu, 3 Jun 2021 13:49:31 +0800 |
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On 6/3/21 7:23 AM, Jason Gunthorpe wrote: > On Wed, Jun 02, 2021 at 12:01:57PM +0800, Lu Baolu wrote: >> On 6/2/21 1:26 AM, Jason Gunthorpe wrote: >>> On Tue, Jun 01, 2021 at 07:09:21PM +0800, Lu Baolu wrote: >>> >>>> This version only covers 1) and 4). Do you think we need to support 2), >>>> 3) and beyond? >>> >>> Yes aboslutely. The API should be flexable enough to specify the >>> creation of all future page table formats we'd want to have and all HW >>> specific details on those formats. >> >> OK, stay in the same line. >> >>>> If so, it seems that we need some in-kernel helpers and uAPIs to >>>> support pre-installing a page table to IOASID. >>> >>> Not sure what this means.. >> >> Sorry that I didn't make this clear. >> >> Let me bring back the page table types in my eyes. >> >> 1) IOMMU format page table (a.k.a. iommu_domain) >> 2) user application CPU page table (SVA for example) >> 3) KVM EPT (future option) >> 4) VM guest managed page table (nesting mode) >> >> Each type of page table should be able to be associated with its IOASID. >> We have BIND protocol for 4); We explicitly allocate an iommu_domain for >> 1). But we don't have a clear definition for 2) 3) and others. I think >> it's necessary to clearly define a time point and kAPI name between >> IOASID_ALLOC and IOASID_ATTACH, so that other modules have the >> opportunity to associate their page table with the allocated IOASID >> before attaching the page table to the real IOMMU hardware. > > In my mind these are all actions of creation.. > > #1 is ALLOC_IOASID 'to be compatible with thes devices attached to > this FD' > #2 is ALLOC_IOASID_SVA > #3 is some ALLOC_IOASID_KVM (and maybe the kvm fd has to issue this ioctl) > #4 is ALLOC_IOASID_USER_PAGE_TABLE w/ user VA address or > ALLOC_IOASID_NESTED_PAGE_TABLE w/ IOVA address > > Each allocation should have a set of operations that are allows > map/unmap is only legal on #1. invalidate is only legal on #4, etc.
This sounds reasonable. The corresponding page table types and required callbacks are also part of it.
> > How you want to split this up in the ioctl interface is a more > interesting question. I generally like more calls than giant unwieldly > multiplexer structs, but some things are naturally flags and optional > modifications of a single ioctl. > > In any event they should have a similar naming 'ALLOC_IOASID_XXX' and > then a single 'DESTROY_IOASID' that works on all of them. > >> I/O page fault handling is similar. The provider of the page table >> should take the responsibility to handle the possible page faults. > > For the faultable types, yes #3 and #4 should hook in the fault > handler and deal with it.
Agreed.
Best regards, baolu
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