// 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;		pos += copylen;	} 	*offset = pos;	return len;}