LXR linux/virt/kvm/binary

   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 */
  52ssize_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