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// SPDX-License-Identifier: GPL-2.0-only
/*
* KVM binary statistics interface implementation
*
* Copyright 2021 Google LLC
*/
#include <linux/kvm_host.h>
#include <linux/kvm.h>
#include <linux/errno.h>
#include <linux/uaccess.h>
/**
* kvm_stats_read() - Common function to read from the binary statistics
* file descriptor.
*
* @id: identification string of the stats
* @header: stats header for a vm or a vcpu
* @desc: start address of an array of stats descriptors for a vm or a vcpu
* @stats: start address of stats data block for a vm or a vcpu
* @size_stats: the size of stats data block pointed by @stats
* @user_buffer: start address of userspace buffer
* @size: requested read size from userspace
* @offset: the start position from which the content will be read for the
* corresponding vm or vcp file descriptor
*
* The file content of a vm/vcpu file descriptor is now defined as below:
* +-------------+
* | Header |
* +-------------+
* | id string |
* +-------------+
* | Descriptors |
* +-------------+
* | Stats Data |
* +-------------+
* Although this function allows userspace to read any amount of data (as long
* as in the limit) from any position, the typical usage would follow below
* steps:
* 1. Read header from offset 0. Get the offset of descriptors and stats data
* and some other necessary information. This is a one-time work for the
* lifecycle of the corresponding vm/vcpu stats fd.
* 2. Read id string from its offset. This is a one-time work for the lifecycle
* of the corresponding vm/vcpu stats fd.
* 3. Read descriptors from its offset and discover all the stats by parsing
* descriptors. This is a one-time work for the lifecycle of the
* corresponding vm/vcpu stats fd.
* 4. Periodically read stats data from its offset using pread.
*
* Return: the number of bytes that has been successfully read
*/
ssize_t 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)
{
ssize_t len;
ssize_t copylen;
ssize_t remain = size;
size_t size_desc;
size_t size_header;
void *src;
loff_t pos = *offset;
char __user *dest = user_buffer;
size_header = sizeof(*header);
size_desc = header->num_desc * sizeof(*desc);
len = KVM_STATS_NAME_SIZE + size_header + size_desc + size_stats - pos;
len = min(len, remain);
if (len <= 0)
return 0;
remain = len;
/*
* Copy kvm stats header.
* The header is the first block of content userspace usually read out.
* The pos is 0 and the copylen and remain would be the size of header.
* The copy of the header would be skipped if offset is larger than the
* size of header. That usually happens when userspace reads stats
* descriptors and stats data.
*/
copylen = size_header - pos;
copylen = min(copylen, remain);
if (copylen > 0) {
src = (void *)header + pos;
if (copy_to_user(dest, src, copylen))
return -EFAULT;
remain -= copylen;
pos += copylen;
dest += copylen;
}
/*
* Copy kvm stats header id string.
* The id string is unique for every vm/vcpu, which is stored in kvm
* and kvm_vcpu structure.
* The id string is part of the stat header from the perspective of
* userspace, it is usually read out together with previous constant
* header part and could be skipped for later descriptors and stats
* data readings.
*/
copylen = header->id_offset + KVM_STATS_NAME_SIZE - pos;
copylen = min(copylen, remain);
if (copylen > 0) {
src = id + pos - header->id_offset;
if (copy_to_user(dest, src, copylen))
return -EFAULT;
remain -= copylen;
pos += copylen;
dest += copylen;
}
/*
* Copy kvm stats descriptors.
* The descriptors copy would be skipped in the typical case that
* userspace periodically read stats data, since the pos would be
* greater than the end address of descriptors
* (header->header.desc_offset + size_desc) causing copylen <= 0.
*/
copylen = header->desc_offset + size_desc - pos;
copylen = min(copylen, remain);
if (copylen > 0) {
src = (void *)desc + pos - header->desc_offset;
if (copy_to_user(dest, src, copylen))
return -EFAULT;
remain -= copylen;
pos += copylen;
dest += copylen;
}
/* Copy kvm stats values */
copylen = header->data_offset + size_stats - pos;
copylen = min(copylen, remain);
if (copylen > 0) {
src = stats + pos - header->data_offset;
if (copy_to_user(dest, src, copylen))
return -EFAULT;
remain -= copylen;
pos += copylen;
dest += copylen;
}
*offset = pos;
return len;
}
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