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 pos += copylen;
140 }
141
142 *offset = pos;
143 return len;
144 }
145
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