1 .. SPDX-License-Identifier: GPL-2.0
2
3 I/O request handling
4 ====================
5
6 An I/O request of a User VM, which is construc
7 distributed by the ACRN Hypervisor Service Mod
8 corresponding to the address range of the I/O
9 handling are described in the following sectio
10
11 1. I/O request
12 --------------
13
14 For each User VM, there is a shared 4-KByte me
15 communication between the hypervisor and Servi
16 256-byte structure buffer, which is 'struct ac
17 an I/O handler of the hypervisor when a trappe
18 VM. ACRN userspace in the Service VM first all
19 the GPA (Guest Physical Address) of the buffer
20 used as an array of 16 I/O request slots with
21 bytes. This array is indexed by vCPU ID.
22
23 2. I/O clients
24 --------------
25
26 An I/O client is responsible for handling User
27 GPA falls in a certain range. Multiple I/O cli
28 User VM. There is a special client associated
29 default client, that handles all I/O requests
30 any other clients. The ACRN userspace acts as
31 VM.
32
33 Below illustration shows the relationship betw
34 I/O requests and I/O clients.
35
36 ::
37
38 +----------------------------------------
39 | S
40 |+---------------------------------------
41 || +--------------------------------
42 || | shared page ACRN use
43 || | +-----------------+ +------
44 || +----+->| acrn_io_request |<-+ defa
45 || | | | +-----------------+ | I/O c
46 || | | | | ... | +------
47 || | | | +-----------------+
48 || | +-|------------------------------
49 ||---|----|------------------------------
50 || | | k
51 || | | +-----------------
52 || | | | +-------------+
53 || | +--------------+ |
54 || | | | I/O clients |
55 || | | | |
56 || | | +-------------+
57 || | +-----------------
58 |+---|-----------------------------------
59 +----|-----------------------------------
60 |
61 +----|-----------------------------------
62 | +-+-----------+
63 | | I/O handler | ACRN Hype
64 | +-------------+
65 +----------------------------------------
66
67 3. I/O request state transition
68 -------------------------------
69
70 The state transitions of an ACRN I/O request a
71
72 ::
73
74 FREE -> PENDING -> PROCESSING -> COMPLETE -
75
76 - FREE: this I/O request slot is empty
77 - PENDING: a valid I/O request is pending in t
78 - PROCESSING: the I/O request is being process
79 - COMPLETE: the I/O request has been processed
80
81 An I/O request in COMPLETE or FREE state is ow
82 ACRN userspace are in charge of processing the
83
84 4. Processing flow of I/O requests
85 ----------------------------------
86
87 a. The I/O handler of the hypervisor will fill
88 state when a trapped I/O access happens in
89 b. The hypervisor makes an upcall, which is a
90 the Service VM.
91 c. The upcall handler schedules a worker to di
92 d. The worker looks for the PENDING I/O reques
93 registered clients based on the address of
94 their state to PROCESSING, and notifies the
95 e. The notified client handles the assigned I/
96 f. The HSM updates I/O requests states to COMP
97 of the completion via hypercalls.
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