cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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task_barrier.h (3020B)

      1/*
      2 * Copyright 2019 Advanced Micro Devices, Inc.
      3 *
      4 * Permission is hereby granted, free of charge, to any person obtaining a
      5 * copy of this software and associated documentation files (the "Software"),
      6 * to deal in the Software without restriction, including without limitation
      7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
      8 * and/or sell copies of the Software, and to permit persons to whom the
      9 * Software is furnished to do so, subject to the following conditions:
     10 *
     11 * The above copyright notice and this permission notice shall be included in
     12 * all copies or substantial portions of the Software.
     13 *
     14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
     17 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
     18 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
     19 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
     20 * OTHER DEALINGS IN THE SOFTWARE.
     21 *
     22 */
     23#include <linux/semaphore.h>
     24#include <linux/atomic.h>
     25
     26/*
     27 * Reusable 2 PHASE task barrier (randevouz point) implementation for N tasks.
     28 * Based on the Little book of sempahores - https://greenteapress.com/wp/semaphores/
     29 */
     30
     31
     32
     33#ifndef DRM_TASK_BARRIER_H_
     34#define DRM_TASK_BARRIER_H_
     35
     36/*
     37 * Represents an instance of a task barrier.
     38 */
     39struct task_barrier {
     40	unsigned int n;
     41	atomic_t count;
     42	struct semaphore enter_turnstile;
     43	struct semaphore exit_turnstile;
     44};
     45
     46static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
     47						 unsigned int n)
     48{
     49	int i;
     50
     51	for (i = 0 ; i < n; i++)
     52		up(turnstile);
     53}
     54
     55static inline void task_barrier_init(struct task_barrier *tb)
     56{
     57	tb->n = 0;
     58	atomic_set(&tb->count, 0);
     59	sema_init(&tb->enter_turnstile, 0);
     60	sema_init(&tb->exit_turnstile, 0);
     61}
     62
     63static inline void task_barrier_add_task(struct task_barrier *tb)
     64{
     65	tb->n++;
     66}
     67
     68static inline void task_barrier_rem_task(struct task_barrier *tb)
     69{
     70	tb->n--;
     71}
     72
     73/*
     74 * Lines up all the threads BEFORE the critical point.
     75 *
     76 * When all thread passed this code the entry barrier is back to locked state.
     77 */
     78static inline void task_barrier_enter(struct task_barrier *tb)
     79{
     80	if (atomic_inc_return(&tb->count) == tb->n)
     81		task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
     82
     83	down(&tb->enter_turnstile);
     84}
     85
     86/*
     87 * Lines up all the threads AFTER the critical point.
     88 *
     89 * This function is used to avoid any one thread running ahead if the barrier is
     90 *  used repeatedly .
     91 */
     92static inline void task_barrier_exit(struct task_barrier *tb)
     93{
     94	if (atomic_dec_return(&tb->count) == 0)
     95		task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
     96
     97	down(&tb->exit_turnstile);
     98}
     99
    100/* Convinieince function when nothing to be done in between entry and exit */
    101static inline void task_barrier_full(struct task_barrier *tb)
    102{
    103	task_barrier_enter(tb);
    104	task_barrier_exit(tb);
    105}
    106
    107#endif