docs: acrn: Introduce ACRN
Add documentation on the following aspects of ACRN: 1) A brief introduction on the architecture of ACRN. 2) I/O request handling in ACRN. 3) CPUID functions of ACRN. To learn more about ACRN, please go to ACRN project website https://projectacrn.org, or the documentation page https://projectacrn.github.io/. Cc: Dave Hansen <dave.hansen@intel.com> Cc: Sen Christopherson <sean.j.christopherson@intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Fengwei Yin <fengwei.yin@intel.com> Cc: Zhi Wang <zhi.a.wang@intel.com> Cc: Zhenyu Wang <zhenyuw@linux.intel.com> Cc: Yu Wang <yu1.wang@intel.com> Cc: Reinette Chatre <reinette.chatre@intel.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Randy Dunlap <rdunlap@infradead.org> Reviewed-by: Zhi Wang <zhi.a.wang@intel.com> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com> Reviewed-by: Borislav Petkov <bp@suse.de> Signed-off-by: Shuo Liu <shuo.a.liu@intel.com> Link: https://lore.kernel.org/r/20210207031040.49576-2-shuo.a.liu@intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Shuo Liu
Greg Kroah-Hartman
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.. SPDX-License-Identifier: GPL-2.0
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===============
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ACRN CPUID bits
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===============
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A guest VM running on an ACRN hypervisor can check some of its features using
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CPUID.
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ACRN cpuid functions are:
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function: 0x40000000
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returns::
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eax = 0x40000010
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ebx = 0x4e524341
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ecx = 0x4e524341
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edx = 0x4e524341
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Note that this value in ebx, ecx and edx corresponds to the string
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"ACRNACRNACRN". The value in eax corresponds to the maximum cpuid function
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present in this leaf, and will be updated if more functions are added in the
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future.
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function: define ACRN_CPUID_FEATURES (0x40000001)
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returns::
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ebx, ecx, edx
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eax = an OR'ed group of (1 << flag)
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where ``flag`` is defined as below:
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================================= =========== ================================
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flag value meaning
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================================= =========== ================================
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ACRN_FEATURE_PRIVILEGED_VM 0 guest VM is a privileged VM
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================================= =========== ================================
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function: 0x40000010
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returns::
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ebx, ecx, edx
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eax = (Virtual) TSC frequency in kHz.
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.. SPDX-License-Identifier: GPL-2.0
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===============
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ACRN Hypervisor
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===============
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.. toctree::
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:maxdepth: 1
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introduction
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io-request
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cpuid
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.. SPDX-License-Identifier: GPL-2.0
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ACRN Hypervisor Introduction
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============================
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The ACRN Hypervisor is a Type 1 hypervisor, running directly on bare-metal
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hardware. It has a privileged management VM, called Service VM, to manage User
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VMs and do I/O emulation.
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ACRN userspace is an application running in the Service VM that emulates
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devices for a User VM based on command line configurations. ACRN Hypervisor
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Service Module (HSM) is a kernel module in the Service VM which provides
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hypervisor services to the ACRN userspace.
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Below figure shows the architecture.
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::
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Service VM User VM
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+----------------------------+ | +------------------+
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| +--------------+ | | | |
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| |ACRN userspace| | | | |
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| +--------------+ | | | |
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|-----------------ioctl------| | | | ...
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|kernel space +----------+ | | | |
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| | HSM | | | | Drivers |
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| +----------+ | | | |
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+--------------------|-------+ | +------------------+
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+---------------------hypercall----------------------------------------+
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| ACRN Hypervisor |
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+----------------------------------------------------------------------+
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| Hardware |
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+----------------------------------------------------------------------+
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ACRN userspace allocates memory for the User VM, configures and initializes the
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devices used by the User VM, loads the virtual bootloader, initializes the
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virtual CPU state and handles I/O request accesses from the User VM. It uses
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ioctls to communicate with the HSM. HSM implements hypervisor services by
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interacting with the ACRN Hypervisor via hypercalls. HSM exports a char device
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interface (/dev/acrn_hsm) to userspace.
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The ACRN hypervisor is open for contribution from anyone. The source repo is
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available at https://github.com/projectacrn/acrn-hypervisor.
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.. SPDX-License-Identifier: GPL-2.0
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I/O request handling
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====================
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An I/O request of a User VM, which is constructed by the hypervisor, is
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distributed by the ACRN Hypervisor Service Module to an I/O client
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corresponding to the address range of the I/O request. Details of I/O request
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handling are described in the following sections.
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1. I/O request
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--------------
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For each User VM, there is a shared 4-KByte memory region used for I/O requests
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communication between the hypervisor and Service VM. An I/O request is a
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256-byte structure buffer, which is 'struct acrn_io_request', that is filled by
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an I/O handler of the hypervisor when a trapped I/O access happens in a User
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VM. ACRN userspace in the Service VM first allocates a 4-KByte page and passes
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the GPA (Guest Physical Address) of the buffer to the hypervisor. The buffer is
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used as an array of 16 I/O request slots with each I/O request slot being 256
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bytes. This array is indexed by vCPU ID.
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2. I/O clients
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--------------
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An I/O client is responsible for handling User VM I/O requests whose accessed
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GPA falls in a certain range. Multiple I/O clients can be associated with each
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User VM. There is a special client associated with each User VM, called the
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default client, that handles all I/O requests that do not fit into the range of
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any other clients. The ACRN userspace acts as the default client for each User
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VM.
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Below illustration shows the relationship between I/O requests shared buffer,
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I/O requests and I/O clients.
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::
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+------------------------------------------------------+
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| Service VM |
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|+--------------------------------------------------+ |
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|| +----------------------------------------+ | |
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|| | shared page ACRN userspace | | |
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|| | +-----------------+ +------------+ | | |
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|| +----+->| acrn_io_request |<-+ default | | | |
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|| | | | +-----------------+ | I/O client | | | |
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|| | | | | ... | +------------+ | | |
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|| | | | +-----------------+ | | |
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|| | +-|--------------------------------------+ | |
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||---|----|-----------------------------------------| |
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|| | | kernel | |
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|| | | +----------------------+ | |
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|| | | | +-------------+ HSM | | |
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|| | +--------------+ | | | |
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|| | | | I/O clients | | | |
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|| | | | | | | |
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|| | | +-------------+ | | |
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|| | +----------------------+ | |
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|+---|----------------------------------------------+ |
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+----|-------------------------------------------------+
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+----|-------------------------------------------------+
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| +-+-----------+ |
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| | I/O handler | ACRN Hypervisor |
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| +-------------+ |
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+------------------------------------------------------+
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3. I/O request state transition
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-------------------------------
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The state transitions of an ACRN I/O request are as follows.
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::
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FREE -> PENDING -> PROCESSING -> COMPLETE -> FREE -> ...
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- FREE: this I/O request slot is empty
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- PENDING: a valid I/O request is pending in this slot
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- PROCESSING: the I/O request is being processed
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- COMPLETE: the I/O request has been processed
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An I/O request in COMPLETE or FREE state is owned by the hypervisor. HSM and
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ACRN userspace are in charge of processing the others.
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4. Processing flow of I/O requests
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----------------------------------
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a. The I/O handler of the hypervisor will fill an I/O request with PENDING
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state when a trapped I/O access happens in a User VM.
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b. The hypervisor makes an upcall, which is a notification interrupt, to
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the Service VM.
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c. The upcall handler schedules a worker to dispatch I/O requests.
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d. The worker looks for the PENDING I/O requests, assigns them to different
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registered clients based on the address of the I/O accesses, updates
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their state to PROCESSING, and notifies the corresponding client to handle.
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e. The notified client handles the assigned I/O requests.
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f. The HSM updates I/O requests states to COMPLETE and notifies the hypervisor
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of the completion via hypercalls.
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@ -12,6 +12,7 @@ Linux Virtualization Support
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paravirt_ops
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guest-halt-polling
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ne_overview
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acrn/index
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.. only:: html and subproject
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@ -436,6 +436,13 @@ S: Orphan
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F: drivers/platform/x86/wmi.c
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F: include/uapi/linux/wmi.h
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ACRN HYPERVISOR SERVICE MODULE
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M: Shuo Liu <shuo.a.liu@intel.com>
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L: acrn-dev@lists.projectacrn.org
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S: Supported
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W: https://projectacrn.org
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F: Documentation/virt/acrn/
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AD1889 ALSA SOUND DRIVER
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L: linux-parisc@vger.kernel.org
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S: Maintained
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