On 04/09/2018 03:12, Xu Zaibo wrote: > On 2018/9/3 18:34, Jean-Philippe Brucker wrote: >> On 01/09/18 03:23, Xu Zaibo wrote: >>> As one application takes a whole function while using VFIO-PCI, why do >>> the application and the >>> function need to enable PASID capability? (Since just one I/O page table >>> is enough for them.) >> At the moment the series doesn't provide support for SVA without PASID >> (on the I/O page fault path, 08/40). In addition the BIND ioctl could be >> used by the owner application to bind other processes (slaves) and >> perform sub-assignment. But that feature is incomplete because we don't >> send stop_pasid notification to the owner when a slave dies. >> > So, Could I understand like this? > > 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. > 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. Thanks, Jean
