> From: Jean-Philippe Brucker [mailto:jean-philippe.brucker@xxxxxxx] > Sent: Monday, August 7, 2017 8:52 PM > > Hi Bob, > > On 07/08/17 13:18, Bob Liu wrote: > > On 2017/8/7 18:31, Jean-Philippe Brucker wrote: > >> On 05/08/17 06:14, valmiki wrote: > >> [...] > >>> Hi Jean, Thanks a lot, now i understood the flow. From vfio kernel > >>> documentation we fill vaddr and iova in struct > vfio_iommu_type1_dma_map > >>> and pass them to VFIO. But if we use dynamic allocation in application > >>> (say malloc), do we need to use dma API to get iova and then call > >>> VFIO_IOMMU_MAP ioctl ? > >>> If application needs multiple such dynamic allocations, then it need to > >>> allocate large chunk and program it via VFIO_IOMMU_MAP ioctl and > then > >>> manage rest allocations requirements from this buffer ? > >> > >> Yes, without SVM, the application allocates large buffers, allocates IOVAs > >> itself, and maps them with VFIO_IOMMU_MAP. Userspace doesn't rely on > the > >> DMA API at all, it manages IOVAs as it wants. Sizes passed to > >> VFIO_IOMMU_MAP have to be multiples of the MMU or IOMMU page > granularity > >> (that is at least 4kB), and both iova and vaddr have to be aligned on that > >> granularity as well. So malloc isn't really suitable in this case, you'll > >> need mmap. The application can then implement a small allocator to > manage > >> the DMA pool created with VFIO_IOMMU_MAP. > >> > >> With SVM the application binds its address space to the device, and then > >> uses malloc for all DMA buffers, no need for VFIO_IOMMU_MAP. > >> > > > > Hi Jean, > > > > I think there is another way to support SVM without PASID. > > > > Suppose there is a device in the same SOC-chip, the device access memory > through SMMU(using internal bus instead of PCIe) > > Once page fault, the device send an event with (vaddr, substreamID) to > SMMU, then SMMU triggers an event interrupt. > > > > In the event interrupt handler, we can implement the same logic as PRI > interrupt in your patch. > > What do you think about that? > What you're describing is the SMMU stall model for platform devices. From > the driver perspective it's the same as PRI and PASID (SubstreamID=PASID). > > When a stall-capable device accesses unmapped memory, the SMMU parks > the > transaction and sends an event marked "stall" on the event queue, with a > stall tag (STAG, roughly equivalent to PRG Index). The OS handles the > fault and sends a CMD_RESUME command with the status and the STAG. > Then > the SMMU completes the access or terminates it. Can such platform device send multiple SubstreamIDs, or one ID per device? Thanks Kevin
