Uacce (Unified/User-space-access-intended Accelerator Framework) targets to provide Shared Virtual Addressing (SVA) between accelerators and processes. So accelerator can access any data structure of the main cpu. This differs from the data sharing between cpu and io device, which share data content rather than address. Because of unified address, hardware and user space of process can share the same virtual address in the communication. Uacce is intended to be used with Jean Philippe Brucker's SVA patchset[1], which enables IO side page fault and PASID support. We have keep verifying with Jean's sva/current [2] We also keep verifying with Eric's SMMUv3 Nested Stage patch [3] This series and related zip & qm driver https://github.com/Linaro/linux-kernel-warpdrive/tree/5.4-rc4-uacce-v8 The library and user application: https://github.com/Linaro/warpdrive/tree/wdprd-upstream-v8 References: [1] http://jpbrucker.net/sva/ [2] http://www.linux-arm.org/git?p=linux-jpb.git;a=shortlog;h=refs/heads/sva/current [3] https://github.com/eauger/linux/tree/v5.3.0-rc0-2stage-v9 Change History: v8: Address some comments from Jonathan Merge Jean's patch, using uacce_mm instead of pid for sva_exit v7: As suggested by Jean and Jerome Only consider sva case and remove unused dma apis for the first patch. Also add mm_exit for sva and vm_ops.close etc v6: https://lkml.org/lkml/2019/10/16/231 Change sys qfrs_size to different file, suggested by Jonathan Fix crypto daily build issue and based on crypto code base, also 5.4-rc1. v5: https://lkml.org/lkml/2019/10/14/74 Add an example patch using the uacce interface, suggested by Greg 0003-crypto-hisilicon-register-zip-engine-to-uacce.patch v4: https://lkml.org/lkml/2019/9/17/116 Based on 5.4-rc1 Considering other driver integrating uacce, if uacce not compiled, uacce_register return error and uacce_unregister is empty. Simplify uacce flag: UACCE_DEV_SVA. Address Greg's comments: Fix state machine, remove potential syslog triggered from user space etc. v3: https://lkml.org/lkml/2019/9/2/990 Recommended by Greg, use sturct uacce_device instead of struct uacce, and use struct *cdev in struct uacce_device, as a result, cdev can be released by itself when refcount decreased to 0. So the two structures are decoupled and self-maintained by themsleves. Also add dev.release for put_device. v2: https://lkml.org/lkml/2019/8/28/565 Address comments from Greg and Jonathan Modify interface uacce_register Drop noiommu mode first v1: https://lkml.org/lkml/2019/8/14/277 1. Rebase to 5.3-rc1 2. Build on iommu interface 3. Verifying with Jean's sva and Eric's nested mode iommu. 4. User library has developed a lot: support zlib, openssl etc. 5. Move to misc first RFC3: https://lkml.org/lkml/2018/11/12/1951 RFC2: https://lwn.net/Articles/763990/ Background of why Uacce: Von Neumann processor is not good at general data manipulation. It is designed for control-bound rather than data-bound application. The latter need less control path facility and more/specific ALUs. So there are more and more heterogeneous processors, such as encryption/decryption accelerators, TPUs, or EDGE (Explicated Data Graph Execution) processors, introduced to gain better performance or power efficiency for particular applications these days. There are generally two ways to make use of these heterogeneous processors: The first is to make them co-processors, just like FPU. This is good for some application but it has its own cons: It changes the ISA set permanently. You must save all state elements when the process is switched out. But most data-bound processors have a huge set of state elements. It makes the kernel scheduler more complex. The second is Accelerator. It is taken as a IO device from the CPU's point of view (but it need not to be physically). The process, running on CPU, hold a context of the accelerator and send instructions to it as if it calls a function or thread running with FPU. The context is bound with the processor itself. So the state elements remain in the hardware context until the context is released. We believe this is the core feature of an "Accelerator" vs. Co-processor or other heterogeneous processors. The intention of Uacce is to provide the basic facility to backup this scenario. Its first step is to make sure the accelerator and process can share the same address space. So the accelerator ISA can directly address any data structure of the main CPU. This differs from the data sharing between CPU and IO device, which share data content rather than address. So it is different comparing to the other DMA libraries. In the future, we may add more facility to support linking accelerator library to the main application, or managing the accelerator context as special thread. But no matter how, this can be a solid start point for new processor to be used as an "accelerator" as this is the essential requirement. The Fork Scenario ================= For a process with allocated queues and shared memory, what happen if it forks a child? The fd of the queue is duplicated on fork, but requests sent from the child process are blocked. It is recommended to add O_CLOEXEC to the queue file. The queue mmap space has a VM_DONTCOPY in its VMA. So the child will lose all those VMAs. This is a reason why Uacce does not adopt the mode used in VFIO and InfiniBand. Both solutions can set any user pointer for hardware sharing. But they cannot support fork when the dma is in process. Or the "Copy-On-Write" procedure will make the parent process lost its physical pages. Difference to the VFIO and IB framework --------------------------------------- The essential function of Uacce is to let the device access the user address directly. There are many device drivers doing the same in the kernel. And both VFIO and IB can provide similar functions in framework level. But Uacce has a different goal: "share address space". It is not taken the request to the accelerator as an enclosure data structure. It takes the accelerator as another thread of the same process. So the accelerator can refer to any address used by the process. Both VFIO and IB are taken this as "memory sharing", not "address sharing". They care more on sharing the block of memory. But if there is an address stored in the block and referring to another memory region. The address may not be valid. By adding more constraints to the VFIO and IB framework, in some sense, we may achieve a similar goal. But we gave it up finally. Both VFIO and IB have extra assumption which is unnecessary to Uacce. They may hurt each other if we try to merge them together. VFIO manages resource of a hardware as a "virtual device". If a device need to serve a separated application. It must isolate the resource as a separate virtual device. And the life cycle of the application and virtual device are unnecessary unrelated. And most concepts, such as bus, driver, probe and so on, to make it as a "device" is unnecessary either. And the logic added to VFIO to make address sharing do no help on "creating a virtual device". IB creates a "verbs" standard for sharing memory region to another remote entity. Most of these verbs are to make memory region between entities to be synchronized. This is not what accelerator need. Accelerator is in the same memory system with the CPU. It refers to the same memory system among CPU and devices. So the local memory terms/verbs are good enough for it. Extra "verbs" are not necessary. And its queue (like queue pair in IB) is the communication channel direct to the accelerator hardware. There is nothing about memory itself. Further, both VFIO and IB use the "pin" (get_user_page) way to lock local memory in place. This is flexible. But it can cause other problems. For example, if the user process fork a child process. The COW procedure may make the parent process lost its pages which are sharing with the device. These may be fixed in the future. But is not going to be easy. (There is a discussion about this on Linux Plumbers Conference 2018 [1]) So we choose to build the solution directly on top of IOMMU interface. IOMMU is the essential way for device and process to share their page mapping from the hardware perspective. It will be safe to create a software solution on this assumption. Uacce manages the IOMMU interface for the accelerator device, so the device driver can export some of the resources to the user space. Uacce than can make sure the device and the process have the same address space. References ========== .. [1] https://lwn.net/Articles/774411/ Kenneth Lee (2): uacce: Add documents for uacce uacce: add uacce driver Zhangfei Gao (1): crypto: hisilicon - register zip engine to uacce Documentation/ABI/testing/sysfs-driver-uacce | 53 +++ Documentation/misc-devices/uacce.rst | 159 +++++++ drivers/crypto/hisilicon/qm.c | 256 ++++++++++- drivers/crypto/hisilicon/qm.h | 11 + drivers/crypto/hisilicon/zip/zip_main.c | 38 +- drivers/misc/Kconfig | 1 + drivers/misc/Makefile | 1 + drivers/misc/uacce/Kconfig | 13 + drivers/misc/uacce/Makefile | 2 + drivers/misc/uacce/uacce.c | 634 +++++++++++++++++++++++++++ include/linux/uacce.h | 155 +++++++ include/uapi/misc/uacce/hisi_qm.h | 23 + include/uapi/misc/uacce/uacce.h | 36 ++ 13 files changed, 1343 insertions(+), 39 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-driver-uacce create mode 100644 Documentation/misc-devices/uacce.rst create mode 100644 drivers/misc/uacce/Kconfig create mode 100644 drivers/misc/uacce/Makefile create mode 100644 drivers/misc/uacce/uacce.c create mode 100644 include/linux/uacce.h create mode 100644 include/uapi/misc/uacce/hisi_qm.h create mode 100644 include/uapi/misc/uacce/uacce.h -- 2.7.4
