Hi Jean, On 2017/10/6 21:31, Jean-Philippe Brucker wrote: > Following discussions at plumbers and elsewhere, it seems like we need to > unify some of the Shared Virtual Memory (SVM) code, in order to define > clear semantics for the SVM API. > > My previous RFC [1] was centered on the SMMUv3, but some of this code will > need to be reused by the SMMUv2 and virtio-iommu drivers. This second > proposal focuses on abstracting a little more into the core IOMMU API, and > also trying to find common ground for all SVM-capable IOMMUs. > > SVM is, in the context of the IOMMU, sharing page tables between a process > and a device. Traditionally it requires IO Page Fault and Process Address > Space ID capabilities in device and IOMMU. > > * A device driver can bind a process to a device, with iommu_process_bind. > Internally we hold on to the mm and get notified of its activity with an > mmu_notifier. The bond is removed by exit_mm, by a call to > iommu_process_unbind or iommu_detach_device. > > * iommu_process_bind returns a 20-bit PASID (PCI terminology) to the > device driver, which programs it into the device to access the process > address space. > > * The device and the IOMMU support recoverable page faults. This can be > either ATS+PRI for PCI, or platform-specific mechanisms such as Stall > for SMMU. > > Ideally systems wanting to use SVM have to support these three features, > but in practice we'll see implementations supporting just a subset of > them, especially in validation environments. So even if this particular > patchset assumes all three capabilities, it should also be possible to > support PASID without IOPF (by pinning everything, see non-system SVM in > OpenCL) How to pin everything? If user malloc anything we should pin it. It should from user or driver? > , or IOPF without PASID (sharing the single device address space > with a process, could be useful for DPDK+VFIO). > > Implementing both these cases would enable PT sharing alone. Some people > would also like IOPF alone without SVM (covered by this series) or process > management without shared PT (not covered). Using these features > individually is also important for testing, as SVM is in its infancy and > providing easy ways to test is essential to reduce the number of quirks > down the line. > > Process management > ================== > > The first part of this series introduces boilerplate code for managing > PASIDs and processes bound to devices. It's something any IOMMU driver > that wants to support bind/unbind will have to do, and it is difficult to > get right. > > Patches > 1: iommu_process and PASID allocation, attach and release > 2: process_exit callback for device drivers > 3: iommu_process search by PASID > 4: track process changes with an MMU notifiers > 5: bind and unbind operations > > My proposal uses the following model: > > * The PASID space is system-wide. This means that a Linux process will > have a single PASID. I introduce the iommu_process structure and a > global IDR to manage this. > > * An iommu_process can be bound to multiple domains, and a domain can have > multiple iommu_process. when bind a task to device, can we create a single domain for it? I am thinking about process management without shared PT(for some device only support PASID without pri ability), it seems hard to expand if a domain have multiple iommu_process? Do you have any idea about this? > > * IOMMU groups share same PASID table. IOMMU groups are a convenient way > to cover various hardware weaknesses that prevent a group of device to > be isolated by the IOMMU (untrusted bridge, for instance). It's foolish > to assume that all PASID implementations will perfectly isolate devices > within a bus and functions within a device, so let's assume all devices > within an IOMMU group have to share PASID traffic as well. In general > there will be a single device per group. > > * It's up to the driver implementation to decide where to implement the > PASID tables. For SMMU it's more convenient to have a single PASID table > per domain. And I think the model fits better with the existing IOMMU > API: IOVA traffic is shared by all devices in a domain, so should PASID > traffic. What's the meaning of "share PASID traffic"? PASID space is system-wide, and a domain can have multiple iommu_process , so a domain can have multiple PASIDs , one PASID for a iommu_process, right? Yisheng Xie Thanks -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
