Documentation/virt/acrn/io-request.rst

Source file repositories/reference/linux-study-clean/Documentation/virt/acrn/io-request.rst

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Corpus path: Documentation/virt/acrn/io-request.rst
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Domain: Support Tooling And Documentation
Bucket: Documentation
Inferred role: Support Tooling And Documentation: documentation
Status: atlas-only

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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
Defines or uses C structs; map object ownership, embedded links, reference counts, and lock ownership.

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.. SPDX-License-Identifier: GPL-2.0

I/O request handling
====================

An I/O request of a User VM, which is constructed by the hypervisor, is
distributed by the ACRN Hypervisor Service Module to an I/O client
corresponding to the address range of the I/O request. Details of I/O request
handling are described in the following sections.

1. I/O request
--------------

For each User VM, there is a shared 4-KByte memory region used for I/O requests
communication between the hypervisor and Service VM. An I/O request is a
256-byte structure buffer, which is 'struct acrn_io_request', that is filled by
an I/O handler of the hypervisor when a trapped I/O access happens in a User
VM. ACRN userspace in the Service VM first allocates a 4-KByte page and passes
the GPA (Guest Physical Address) of the buffer to the hypervisor. The buffer is
used as an array of 16 I/O request slots with each I/O request slot being 256
bytes. This array is indexed by vCPU ID.

2. I/O clients
--------------

An I/O client is responsible for handling User VM I/O requests whose accessed
GPA falls in a certain range. Multiple I/O clients can be associated with each
User VM. There is a special client associated with each User VM, called the
default client, that handles all I/O requests that do not fit into the range of
any other clients. The ACRN userspace acts as the default client for each User
VM.

Below illustration shows the relationship between I/O requests shared buffer,
I/O requests and I/O clients.

::

     +------------------------------------------------------+
     |                                       Service VM     |
     |+--------------------------------------------------+  |
     ||      +----------------------------------------+  |  |
     ||      | shared page            ACRN userspace  |  |  |
     ||      |    +-----------------+  +------------+ |  |  |
     ||   +----+->| acrn_io_request |<-+  default   | |  |  |
     ||   |  | |  +-----------------+  | I/O client | |  |  |
     ||   |  | |  |       ...       |  +------------+ |  |  |
     ||   |  | |  +-----------------+                 |  |  |
     ||   |  +-|--------------------------------------+  |  |
     ||---|----|-----------------------------------------|  |
     ||   |    |                             kernel      |  |
     ||   |    |            +----------------------+     |  |
     ||   |    |            | +-------------+  HSM |     |  |
     ||   |    +--------------+             |      |     |  |
     ||   |                 | | I/O clients |      |     |  |
     ||   |                 | |             |      |     |  |
     ||   |                 | +-------------+      |     |  |
     ||   |                 +----------------------+     |  |
     |+---|----------------------------------------------+  |
     +----|-------------------------------------------------+
          |
     +----|-------------------------------------------------+
     |  +-+-----------+                                     |
     |  | I/O handler |              ACRN Hypervisor        |
     |  +-------------+                                     |
     +------------------------------------------------------+

3. I/O request state transition
-------------------------------

The state transitions of an ACRN I/O request are as follows.

Annotation

Atlas domain: Support Tooling And Documentation / Documentation.
Implementation status: atlas-only.

Implementation Notes

This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.