Hi, [Adding David and Greg in CC]
On 2/8/21 7:37 PM, Peter Xu wrote: > On Mon, Feb 08, 2021 at 11:21:23AM +0800, Jason Wang wrote: > > [...] > >>> I'm not sure I remember it right, but we seem to have similar discussion >>> previously on "what if the user didn't specify ats=on" - I think at that >>> time >>> the conclusion was that we ignore the failure since that's not a valid >>> configuration for qemu. >> >> >> Yes, but I think I was wrong at that time. > > I can't say you're wrong - I actually still agree with you that at least > there's a priority of things we'd do, and this one is not extremely important > if that's not a major use case (say, if you will 100% always suggest an user > to > use ats=on for a viommu enabled vhost). > >>> >>> The other issue I'm worried is (I think I mentioned it somewhere, but just >>> to >>> double confirm): I'd like to make sure SMMU and virtio-iommu are the only >>> IOMMU >>> platform that will use vhost. >> >> >> For upstream, it won't be easy :) > > Sorry I definitely didn't make myself clear... :) > > To be explicit, does ppc use vhost kernel too? Since I know at least ppc has > its own translation unit and its iommu notifier in qemu, so I'm unsure whether > the same patch would break ppc too, because vhost could also ignore all UNMAP > sent by the ppc vIOMMU. > >> >> >>> Otherwise IIUC we need to fix those vIOMMUs too. >> >> >> Right, last time I check AMD IOMMU emulation, it simply trigger device IOTLB >> invalidation during IOTLB invalidation which looks wrong. > > I did quickly grep IOMMU_NOTIFIER_UNMAP in amd_iommu.c and saw nothing. It > seems amd iommu is not ready for any kind of IOMMU notifiers yet. for context, we experienced a regression with vsmmuv3/vhost and virtio-iommu/vhost integration. We wondered whether the ppc viommu is able to protect vhost devices and if this relies on legacy IOMMU_NOTIFIER_UNMAP notifiers. ie. vhost does not register this notifier anymore but instead register dev-iotlb unmap notifier. Thanks Eric > > Thanks, >