On 05/09/2018 04:15, Xu Zaibo wrote: >>> 1. While the series are finished well, VFIO-PCI device can be held >>> by only one process >>> through binding IOCTL command without PASID (without PASID >>> being exposed user space). >> It could, but isn't supported at the moment. In addition to adding >> support in the I/O page fault code, we'd also need to update the VFIO >> API. Currently a VFIO_TYPE1 domain always supports the MAP/UNMAP ioctl. >> The case you describe isn't compatible with MAP/UNMAP, since the process >> manages the shared address space with mmap or malloc. We'd probably need >> to introduce a new VFIO IOMMU type, in which case the bind could be >> performed implicitly when the process does VFIO_SET_IOMMU. Then the >> process wouldn't need to send an additional BIND IOCTL. > ok. got it. This is the legacy mode, so all the VFIO APIs are kept > unchanged? Yes, existing VFIO semantics are preserved >>> 2. While using VFIO-PCI device to support multiple processes with >>> SVA series, a primary >>> process with multiple secondary processes must be deployed just >>> like DPDK(https://www.dpdk.org/). >>> And, the PASID still has to be exposed to user land. >> Right. A third case, also implemented by this patch (and complete), is >> the primary process simply doing a BIND for itself, and using the >> returned PASID to share its own address space with the device. >> > ok. But I am worried that the sulotion of one primary processes with > several secondary ones > > is a little bit limited. Maybe, users don't want to depend on the > primary process. :) I don't see a better way for vfio-pci, though. But more importantly, I don't know of any users :) While the feature is great for testing new hardware, and I've been using it for all kinds of stress testing, I haven't received feedback from possible users in production settings (DPDK etc) and can't speculate about what they'd prefer. Thanks, Jean
