Kevin, On Mon, Feb 08, 2021 at 07:03:08AM +0000, Tian, Kevin wrote: > It really depends on the definition of dev-iotlb in this context. To me the > fact that virtio-iommu needs to notify the kernel for updating split cache > is already sort of dev-iotlb semantics, regardless of whether it's delivered > through a iotlb message or dev-iotlb message in a specific implementation. 😊
Yeah maybe it turns out that we'll just need to implement dev-iotlb for virtio-iommu. I am completely fine with that and I'm never against it. :) I was throwing out a pure question only, because I don't know the answer. My question was majorly based on the fact that dev-iotlb and iotlb messages really look the same; it's not obvious then whether it would always matter a lot when in a full emulation environment. One example is current vhost - vhost previously would work without dev-iotlb (ats=on) because trapping UNMAP would work too for vhost to work. It's also simply because at least for VT-d the driver needs to send both one dev-iotlb and one (probably same) iotlb message for a single page invalidation. The dev-iotlb won't help a lot in full emulation here but instead it slows thing down a little bit (QEMU has full knowledge as long as it receives either of the message). Thanks, -- Peter Xu
