Messages in this thread | | | Date | Wed, 22 Jun 2022 08:54:45 +0100 | Subject | Re: [PATCH v2 3/5] vfio/iommu_type1: Remove the domain->ops comparison | From | Robin Murphy <> |
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On 2022-06-16 23:23, Nicolin Chen wrote: > On Thu, Jun 16, 2022 at 06:40:14AM +0000, Tian, Kevin wrote: > >>> The domain->ops validation was added, as a precaution, for mixed-driver >>> systems. However, at this moment only one iommu driver is possible. So >>> remove it. >> >> It's true on a physical platform. But I'm not sure whether a virtual platform >> is allowed to include multiple e.g. one virtio-iommu alongside a virtual VT-d >> or a virtual smmu. It might be clearer to claim that (as Robin pointed out) >> there is plenty more significant problems than this to solve instead of simply >> saying that only one iommu driver is possible if we don't have explicit code >> to reject such configuration. 😊 > > Will edit this part. Thanks!
Oh, physical platforms with mixed IOMMUs definitely exist already. The main point is that while bus_set_iommu still exists, the core code effectively *does* prevent multiple drivers from registering - even in emulated cases like the example above, virtio-iommu and VT-d would both try to bus_set_iommu(&pci_bus_type), and one of them will lose. The aspect which might warrant clarification is that there's no combination of supported drivers which claim non-overlapping buses *and* could appear in the same system - even if you tried to contrive something by emulating, say, VT-d (PCI) alongside rockchip-iommu (platform), you could still only describe one or the other due to ACPI vs. Devicetree.
Thanks, Robin.
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