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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * KVM binary statistics interface implementation4 *5 * Copyright 2021 Google LLC6 */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 statistics15 * file descriptor.16 *17 * @id: identification string of the stats18 * @header: stats header for a vm or a vcpu19 * @desc: start address of an array of stats descriptors for a vm or a vcpu20 * @stats: start address of stats data block for a vm or a vcpu21 * @size_stats: the size of stats data block pointed by @stats22 * @user_buffer: start address of userspace buffer23 * @size: requested read size from userspace24 * @offset: the start position from which the content will be read for the25 * corresponding vm or vcp file descriptor26 *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 long38 * as in the limit) from any position, the typical usage would follow below39 * steps:40 * 1. Read header from offset 0. Get the offset of descriptors and stats data41 * and some other necessary information. This is a one-time work for the42 * lifecycle of the corresponding vm/vcpu stats fd.43 * 2. Read id string from its offset. This is a one-time work for the lifecycle44 * of the corresponding vm/vcpu stats fd.45 * 3. Read descriptors from its offset and discover all the stats by parsing46 * descriptors. This is a one-time work for the lifecycle of the47 * 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 read51 */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 the80 * size of header. That usually happens when userspace reads stats81 * 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 kvm97 * and kvm_vcpu structure.98 * The id string is part of the stat header from the perspective of99 * userspace, it is usually read out together with previous constant100 * header part and could be skipped for later descriptors and stats101 * 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 that117 * userspace periodically read stats data, since the pos would be118 * greater than the end address of descriptors119 * (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