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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smp-tbsync.c (3148B)

      1// SPDX-License-Identifier: GPL-2.0
      2/*
      3 * Smp timebase synchronization for ppc.
      4 *
      5 * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se)
      6 *
      7 */
      8
      9#include <linux/kernel.h>
     10#include <linux/sched.h>
     11#include <linux/smp.h>
     12#include <linux/unistd.h>
     13#include <linux/slab.h>
     14#include <linux/atomic.h>
     15#include <asm/smp.h>
     16#include <asm/time.h>
     17
     18#define NUM_ITER		300
     19
     20enum {
     21	kExit=0, kSetAndTest, kTest
     22};
     23
     24static struct {
     25	volatile u64		tb;
     26	volatile u64		mark;
     27	volatile int		cmd;
     28	volatile int		handshake;
     29	int			filler[2];
     30
     31	volatile int		ack;
     32	int			filler2[7];
     33
     34	volatile int		race_result;
     35} *tbsync;
     36
     37static volatile int		running;
     38
     39static void enter_contest(u64 mark, long add)
     40{
     41	while (get_tb() < mark)
     42		tbsync->race_result = add;
     43}
     44
     45void smp_generic_take_timebase(void)
     46{
     47	int cmd;
     48	u64 tb;
     49	unsigned long flags;
     50
     51	local_irq_save(flags);
     52	while (!running)
     53		barrier();
     54	rmb();
     55
     56	for (;;) {
     57		tbsync->ack = 1;
     58		while (!tbsync->handshake)
     59			barrier();
     60		rmb();
     61
     62		cmd = tbsync->cmd;
     63		tb = tbsync->tb;
     64		mb();
     65		tbsync->ack = 0;
     66		if (cmd == kExit)
     67			break;
     68
     69		while (tbsync->handshake)
     70			barrier();
     71		if (cmd == kSetAndTest)
     72			set_tb(tb >> 32, tb & 0xfffffffful);
     73		enter_contest(tbsync->mark, -1);
     74	}
     75	local_irq_restore(flags);
     76}
     77
     78static int start_contest(int cmd, long offset, int num)
     79{
     80	int i, score=0;
     81	u64 tb;
     82	u64 mark;
     83
     84	tbsync->cmd = cmd;
     85
     86	local_irq_disable();
     87	for (i = -3; i < num; ) {
     88		tb = get_tb() + 400;
     89		tbsync->tb = tb + offset;
     90		tbsync->mark = mark = tb + 400;
     91
     92		wmb();
     93
     94		tbsync->handshake = 1;
     95		while (tbsync->ack)
     96			barrier();
     97
     98		while (get_tb() <= tb)
     99			barrier();
    100		tbsync->handshake = 0;
    101		enter_contest(mark, 1);
    102
    103		while (!tbsync->ack)
    104			barrier();
    105
    106		if (i++ > 0)
    107			score += tbsync->race_result;
    108	}
    109	local_irq_enable();
    110	return score;
    111}
    112
    113void smp_generic_give_timebase(void)
    114{
    115	int i, score, score2, old, min=0, max=5000, offset=1000;
    116
    117	pr_debug("Software timebase sync\n");
    118
    119	/* if this fails then this kernel won't work anyway... */
    120	tbsync = kzalloc( sizeof(*tbsync), GFP_KERNEL );
    121	mb();
    122	running = 1;
    123
    124	while (!tbsync->ack)
    125		barrier();
    126
    127	pr_debug("Got ack\n");
    128
    129	/* binary search */
    130	for (old = -1; old != offset ; offset = (min+max) / 2) {
    131		score = start_contest(kSetAndTest, offset, NUM_ITER);
    132
    133		pr_debug("score %d, offset %d\n", score, offset );
    134
    135		if( score > 0 )
    136			max = offset;
    137		else
    138			min = offset;
    139		old = offset;
    140	}
    141	score = start_contest(kSetAndTest, min, NUM_ITER);
    142	score2 = start_contest(kSetAndTest, max, NUM_ITER);
    143
    144	pr_debug("Min %d (score %d), Max %d (score %d)\n",
    145		 min, score, max, score2);
    146	score = abs(score);
    147	score2 = abs(score2);
    148	offset = (score < score2) ? min : max;
    149
    150	/* guard against inaccurate mttb */
    151	for (i = 0; i < 10; i++) {
    152		start_contest(kSetAndTest, offset, NUM_ITER/10);
    153
    154		if ((score2 = start_contest(kTest, offset, NUM_ITER)) < 0)
    155			score2 = -score2;
    156		if (score2 <= score || score2 < 20)
    157			break;
    158	}
    159	pr_debug("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER );
    160
    161	/* exiting */
    162	tbsync->cmd = kExit;
    163	wmb();
    164	tbsync->handshake = 1;
    165	while (tbsync->ack)
    166		barrier();
    167	tbsync->handshake = 0;
    168	kfree(tbsync);
    169	tbsync = NULL;
    170	running = 0;
    171}