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1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | /* | |
3 | * KVM binary statistics interface implementation | |
4 | * | |
5 | * Copyright 2021 Google LLC | |
6 | */ | |
7 | ||
8 | #include <linux/kvm_host.h> | |
9 | #include <linux/kvm.h> | |
10 | #include <linux/errno.h> | |
11 | #include <linux/uaccess.h> | |
12 | ||
13 | /** | |
14 | * kvm_stats_read() - Common function to read from the binary statistics | |
15 | * file descriptor. | |
16 | * | |
17 | * @id: identification string of the stats | |
18 | * @header: stats header for a vm or a vcpu | |
19 | * @desc: start address of an array of stats descriptors for a vm or a vcpu | |
20 | * @stats: start address of stats data block for a vm or a vcpu | |
21 | * @size_stats: the size of stats data block pointed by @stats | |
22 | * @user_buffer: start address of userspace buffer | |
23 | * @size: requested read size from userspace | |
24 | * @offset: the start position from which the content will be read for the | |
25 | * corresponding vm or vcp file descriptor | |
26 | * | |
27 | * The file content of a vm/vcpu file descriptor is now defined as below: | |
28 | * +-------------+ | |
29 | * | Header | | |
30 | * +-------------+ | |
31 | * | id string | | |
32 | * +-------------+ | |
33 | * | Descriptors | | |
34 | * +-------------+ | |
35 | * | Stats Data | | |
36 | * +-------------+ | |
37 | * Although this function allows userspace to read any amount of data (as long | |
38 | * as in the limit) from any position, the typical usage would follow below | |
39 | * steps: | |
40 | * 1. Read header from offset 0. Get the offset of descriptors and stats data | |
41 | * and some other necessary information. This is a one-time work for the | |
42 | * lifecycle of the corresponding vm/vcpu stats fd. | |
43 | * 2. Read id string from its offset. This is a one-time work for the lifecycle | |
44 | * of the corresponding vm/vcpu stats fd. | |
45 | * 3. Read descriptors from its offset and discover all the stats by parsing | |
46 | * descriptors. This is a one-time work for the lifecycle of the | |
47 | * corresponding vm/vcpu stats fd. | |
48 | * 4. Periodically read stats data from its offset using pread. | |
49 | * | |
50 | * Return: the number of bytes that has been successfully read | |
51 | */ | |
52 | ssize_t kvm_stats_read(char *id, const struct kvm_stats_header *header, | |
53 | const struct _kvm_stats_desc *desc, | |
54 | void *stats, size_t size_stats, | |
55 | char __user *user_buffer, size_t size, loff_t *offset) | |
56 | { | |
57 | ssize_t len; | |
58 | ssize_t copylen; | |
59 | ssize_t remain = size; | |
60 | size_t size_desc; | |
61 | size_t size_header; | |
62 | void *src; | |
63 | loff_t pos = *offset; | |
64 | char __user *dest = user_buffer; | |
65 | ||
66 | size_header = sizeof(*header); | |
67 | size_desc = header->num_desc * sizeof(*desc); | |
68 | ||
69 | len = KVM_STATS_NAME_SIZE + size_header + size_desc + size_stats - pos; | |
70 | len = min(len, remain); | |
71 | if (len <= 0) | |
72 | return 0; | |
73 | remain = len; | |
74 | ||
75 | /* | |
76 | * Copy kvm stats header. | |
77 | * The header is the first block of content userspace usually read out. | |
78 | * The pos is 0 and the copylen and remain would be the size of header. | |
79 | * The copy of the header would be skipped if offset is larger than the | |
80 | * size of header. That usually happens when userspace reads stats | |
81 | * descriptors and stats data. | |
82 | */ | |
83 | copylen = size_header - pos; | |
84 | copylen = min(copylen, remain); | |
85 | if (copylen > 0) { | |
86 | src = (void *)header + pos; | |
87 | if (copy_to_user(dest, src, copylen)) | |
88 | return -EFAULT; | |
89 | remain -= copylen; | |
90 | pos += copylen; | |
91 | dest += copylen; | |
92 | } | |
93 | ||
94 | /* | |
95 | * Copy kvm stats header id string. | |
96 | * The id string is unique for every vm/vcpu, which is stored in kvm | |
97 | * and kvm_vcpu structure. | |
98 | * The id string is part of the stat header from the perspective of | |
99 | * userspace, it is usually read out together with previous constant | |
100 | * header part and could be skipped for later descriptors and stats | |
101 | * data readings. | |
102 | */ | |
103 | copylen = header->id_offset + KVM_STATS_NAME_SIZE - pos; | |
104 | copylen = min(copylen, remain); | |
105 | if (copylen > 0) { | |
106 | src = id + pos - header->id_offset; | |
107 | if (copy_to_user(dest, src, copylen)) | |
108 | return -EFAULT; | |
109 | remain -= copylen; | |
110 | pos += copylen; | |
111 | dest += copylen; | |
112 | } | |
113 | ||
114 | /* | |
115 | * Copy kvm stats descriptors. | |
116 | * The descriptors copy would be skipped in the typical case that | |
117 | * userspace periodically read stats data, since the pos would be | |
118 | * greater than the end address of descriptors | |
119 | * (header->header.desc_offset + size_desc) causing copylen <= 0. | |
120 | */ | |
121 | copylen = header->desc_offset + size_desc - pos; | |
122 | copylen = min(copylen, remain); | |
123 | if (copylen > 0) { | |
124 | src = (void *)desc + pos - header->desc_offset; | |
125 | if (copy_to_user(dest, src, copylen)) | |
126 | return -EFAULT; | |
127 | remain -= copylen; | |
128 | pos += copylen; | |
129 | dest += copylen; | |
130 | } | |
131 | ||
132 | /* Copy kvm stats values */ | |
133 | copylen = header->data_offset + size_stats - pos; | |
134 | copylen = min(copylen, remain); | |
135 | if (copylen > 0) { | |
136 | src = stats + pos - header->data_offset; | |
137 | if (copy_to_user(dest, src, copylen)) | |
138 | return -EFAULT; | |
139 | remain -= copylen; | |
140 | pos += copylen; | |
141 | dest += copylen; | |
142 | } | |
143 | ||
144 | *offset = pos; | |
145 | return len; | |
146 | } |