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