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 *, |
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 ; |
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(to: dest, from: src, n: 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(to: dest, from: src, n: 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(to: dest, from: src, n: 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(to: dest, from: src, n: copylen)) |
138 | return -EFAULT; |
139 | pos += copylen; |
140 | } |
141 | |
142 | *offset = pos; |
143 | return len; |
144 | } |
145 | |