1*cb082bfaSJing Zhang // SPDX-License-Identifier: GPL-2.0-only
2*cb082bfaSJing Zhang /*
3*cb082bfaSJing Zhang * KVM binary statistics interface implementation
4*cb082bfaSJing Zhang *
5*cb082bfaSJing Zhang * Copyright 2021 Google LLC
6*cb082bfaSJing Zhang */
7*cb082bfaSJing Zhang
8*cb082bfaSJing Zhang #include <linux/kvm_host.h>
9*cb082bfaSJing Zhang #include <linux/kvm.h>
10*cb082bfaSJing Zhang #include <linux/errno.h>
11*cb082bfaSJing Zhang #include <linux/uaccess.h>
12*cb082bfaSJing Zhang
13*cb082bfaSJing Zhang /**
14*cb082bfaSJing Zhang * kvm_stats_read() - Common function to read from the binary statistics
15*cb082bfaSJing Zhang * file descriptor.
16*cb082bfaSJing Zhang *
17*cb082bfaSJing Zhang * @id: identification string of the stats
18*cb082bfaSJing Zhang * @header: stats header for a vm or a vcpu
19*cb082bfaSJing Zhang * @desc: start address of an array of stats descriptors for a vm or a vcpu
20*cb082bfaSJing Zhang * @stats: start address of stats data block for a vm or a vcpu
21*cb082bfaSJing Zhang * @size_stats: the size of stats data block pointed by @stats
22*cb082bfaSJing Zhang * @user_buffer: start address of userspace buffer
23*cb082bfaSJing Zhang * @size: requested read size from userspace
24*cb082bfaSJing Zhang * @offset: the start position from which the content will be read for the
25*cb082bfaSJing Zhang * corresponding vm or vcp file descriptor
26*cb082bfaSJing Zhang *
27*cb082bfaSJing Zhang * The file content of a vm/vcpu file descriptor is now defined as below:
28*cb082bfaSJing Zhang * +-------------+
29*cb082bfaSJing Zhang * | Header |
30*cb082bfaSJing Zhang * +-------------+
31*cb082bfaSJing Zhang * | id string |
32*cb082bfaSJing Zhang * +-------------+
33*cb082bfaSJing Zhang * | Descriptors |
34*cb082bfaSJing Zhang * +-------------+
35*cb082bfaSJing Zhang * | Stats Data |
36*cb082bfaSJing Zhang * +-------------+
37*cb082bfaSJing Zhang * Although this function allows userspace to read any amount of data (as long
38*cb082bfaSJing Zhang * as in the limit) from any position, the typical usage would follow below
39*cb082bfaSJing Zhang * steps:
40*cb082bfaSJing Zhang * 1. Read header from offset 0. Get the offset of descriptors and stats data
41*cb082bfaSJing Zhang * and some other necessary information. This is a one-time work for the
42*cb082bfaSJing Zhang * lifecycle of the corresponding vm/vcpu stats fd.
43*cb082bfaSJing Zhang * 2. Read id string from its offset. This is a one-time work for the lifecycle
44*cb082bfaSJing Zhang * of the corresponding vm/vcpu stats fd.
45*cb082bfaSJing Zhang * 3. Read descriptors from its offset and discover all the stats by parsing
46*cb082bfaSJing Zhang * descriptors. This is a one-time work for the lifecycle of the
47*cb082bfaSJing Zhang * corresponding vm/vcpu stats fd.
48*cb082bfaSJing Zhang * 4. Periodically read stats data from its offset using pread.
49*cb082bfaSJing Zhang *
50*cb082bfaSJing Zhang * Return: the number of bytes that has been successfully read
51*cb082bfaSJing Zhang */
kvm_stats_read(char * id,const struct kvm_stats_header * header,const struct _kvm_stats_desc * desc,void * stats,size_t size_stats,char __user * user_buffer,size_t size,loff_t * offset)52*cb082bfaSJing Zhang ssize_t kvm_stats_read(char *id, const struct kvm_stats_header *header,
53*cb082bfaSJing Zhang const struct _kvm_stats_desc *desc,
54*cb082bfaSJing Zhang void *stats, size_t size_stats,
55*cb082bfaSJing Zhang char __user *user_buffer, size_t size, loff_t *offset)
56*cb082bfaSJing Zhang {
57*cb082bfaSJing Zhang ssize_t len;
58*cb082bfaSJing Zhang ssize_t copylen;
59*cb082bfaSJing Zhang ssize_t remain = size;
60*cb082bfaSJing Zhang size_t size_desc;
61*cb082bfaSJing Zhang size_t size_header;
62*cb082bfaSJing Zhang void *src;
63*cb082bfaSJing Zhang loff_t pos = *offset;
64*cb082bfaSJing Zhang char __user *dest = user_buffer;
65*cb082bfaSJing Zhang
66*cb082bfaSJing Zhang size_header = sizeof(*header);
67*cb082bfaSJing Zhang size_desc = header->num_desc * sizeof(*desc);
68*cb082bfaSJing Zhang
69*cb082bfaSJing Zhang len = KVM_STATS_NAME_SIZE + size_header + size_desc + size_stats - pos;
70*cb082bfaSJing Zhang len = min(len, remain);
71*cb082bfaSJing Zhang if (len <= 0)
72*cb082bfaSJing Zhang return 0;
73*cb082bfaSJing Zhang remain = len;
74*cb082bfaSJing Zhang
75*cb082bfaSJing Zhang /*
76*cb082bfaSJing Zhang * Copy kvm stats header.
77*cb082bfaSJing Zhang * The header is the first block of content userspace usually read out.
78*cb082bfaSJing Zhang * The pos is 0 and the copylen and remain would be the size of header.
79*cb082bfaSJing Zhang * The copy of the header would be skipped if offset is larger than the
80*cb082bfaSJing Zhang * size of header. That usually happens when userspace reads stats
81*cb082bfaSJing Zhang * descriptors and stats data.
82*cb082bfaSJing Zhang */
83*cb082bfaSJing Zhang copylen = size_header - pos;
84*cb082bfaSJing Zhang copylen = min(copylen, remain);
85*cb082bfaSJing Zhang if (copylen > 0) {
86*cb082bfaSJing Zhang src = (void *)header + pos;
87*cb082bfaSJing Zhang if (copy_to_user(dest, src, copylen))
88*cb082bfaSJing Zhang return -EFAULT;
89*cb082bfaSJing Zhang remain -= copylen;
90*cb082bfaSJing Zhang pos += copylen;
91*cb082bfaSJing Zhang dest += copylen;
92*cb082bfaSJing Zhang }
93*cb082bfaSJing Zhang
94*cb082bfaSJing Zhang /*
95*cb082bfaSJing Zhang * Copy kvm stats header id string.
96*cb082bfaSJing Zhang * The id string is unique for every vm/vcpu, which is stored in kvm
97*cb082bfaSJing Zhang * and kvm_vcpu structure.
98*cb082bfaSJing Zhang * The id string is part of the stat header from the perspective of
99*cb082bfaSJing Zhang * userspace, it is usually read out together with previous constant
100*cb082bfaSJing Zhang * header part and could be skipped for later descriptors and stats
101*cb082bfaSJing Zhang * data readings.
102*cb082bfaSJing Zhang */
103*cb082bfaSJing Zhang copylen = header->id_offset + KVM_STATS_NAME_SIZE - pos;
104*cb082bfaSJing Zhang copylen = min(copylen, remain);
105*cb082bfaSJing Zhang if (copylen > 0) {
106*cb082bfaSJing Zhang src = id + pos - header->id_offset;
107*cb082bfaSJing Zhang if (copy_to_user(dest, src, copylen))
108*cb082bfaSJing Zhang return -EFAULT;
109*cb082bfaSJing Zhang remain -= copylen;
110*cb082bfaSJing Zhang pos += copylen;
111*cb082bfaSJing Zhang dest += copylen;
112*cb082bfaSJing Zhang }
113*cb082bfaSJing Zhang
114*cb082bfaSJing Zhang /*
115*cb082bfaSJing Zhang * Copy kvm stats descriptors.
116*cb082bfaSJing Zhang * The descriptors copy would be skipped in the typical case that
117*cb082bfaSJing Zhang * userspace periodically read stats data, since the pos would be
118*cb082bfaSJing Zhang * greater than the end address of descriptors
119*cb082bfaSJing Zhang * (header->header.desc_offset + size_desc) causing copylen <= 0.
120*cb082bfaSJing Zhang */
121*cb082bfaSJing Zhang copylen = header->desc_offset + size_desc - pos;
122*cb082bfaSJing Zhang copylen = min(copylen, remain);
123*cb082bfaSJing Zhang if (copylen > 0) {
124*cb082bfaSJing Zhang src = (void *)desc + pos - header->desc_offset;
125*cb082bfaSJing Zhang if (copy_to_user(dest, src, copylen))
126*cb082bfaSJing Zhang return -EFAULT;
127*cb082bfaSJing Zhang remain -= copylen;
128*cb082bfaSJing Zhang pos += copylen;
129*cb082bfaSJing Zhang dest += copylen;
130*cb082bfaSJing Zhang }
131*cb082bfaSJing Zhang
132*cb082bfaSJing Zhang /* Copy kvm stats values */
133*cb082bfaSJing Zhang copylen = header->data_offset + size_stats - pos;
134*cb082bfaSJing Zhang copylen = min(copylen, remain);
135*cb082bfaSJing Zhang if (copylen > 0) {
136*cb082bfaSJing Zhang src = stats + pos - header->data_offset;
137*cb082bfaSJing Zhang if (copy_to_user(dest, src, copylen))
138*cb082bfaSJing Zhang return -EFAULT;
139*cb082bfaSJing Zhang pos += copylen;
140*cb082bfaSJing Zhang }
141*cb082bfaSJing Zhang
142*cb082bfaSJing Zhang *offset = pos;
143*cb082bfaSJing Zhang return len;
144*cb082bfaSJing Zhang }
145