Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 6 Apr 2022 13:32:07 +0100 | Subject | Re: [PATCH RFC v2 03/11] iommu/sva: Add iommu_domain type for SVA | From | Robin Murphy <> |
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On 2022-04-06 06:58, Tian, Kevin wrote: >> From: Jason Gunthorpe <jgg@nvidia.com> >> Sent: Wednesday, April 6, 2022 9:24 AM >> >> On Wed, Apr 06, 2022 at 01:00:13AM +0000, Tian, Kevin wrote: >> >>>> Because domains wrap more than just the IOPTE format, they have >>>> additional data related to the IOMMU HW block itself. Imagine a SOC >>>> with two IOMMU HW blocks that can both process the CPU IOPTE format, >>>> but have different configuration. >>> >>> Curious. Is it hypothesis or real? If real can you help give a concrete >>> example? >> >> Look at arm_smmu_attach_dev() - the domain has exactly one smmu >> pointer which contains the base address for the SMMU IP block. If the >> domain doesn't match the smmu pointer from the struct device it won't >> allow attaching. >> >> I know of ARM SOCs with many copies of the SMMU IP block. >> >> So at least with current drivers ARM seems to have this limitation. >> > > I saw that code, but before this series it is used only for stage-2 instead > of SVA. and I didn't see similar check in the old sva related paths (though > it doesn't use domain): > > arm_smmu_master_sva_enable_iopf() > arm_smmu_master_enable_sva{} > __arm_smmu_sva_bind() > > If I didn't overlook some trick hiding in the call chain of those functions, > is there a bug in the existing SMMU sva logic or is it conceptually correct > to not have such check for SVA?
The current SVA APIs are all device-based, so implicitly reflect whichever SMMU instance serves the given device. Once domains come into the picture, callers are going to have to be more aware that a domain may be specific to a particular IOMMU instance, and potentially allocate separate domains for separate devices to represent the same address space, much like vfio_iommu_type1_attach_group() does.
It's not really worth IOMMU drivers trying to support a domain spanning potentially-heterogeneous instances internally, since they can't reasonably know what matters in any particular situation. That's primarily why we've never tried to do it in the SMMU drivers. It's a lot easier for relevant callers to look at what they get and figure out whether any mismatch in capabilities is tolerable or not.
Robin.
> If the former then yes we have to take SMMU IP block into consideration > thus could have multiple domains per CPU page table. If the latter then > this is not a valid example for that configuration. > > Which one is correct? > > Thanks > Kevin
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