summaryrefslogtreecommitdiff
path: root/arch/arc/include/asm/mmu_context.h
blob: 035470816be55e578e94bededfe8f544b12750f2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * vineetg: May 2011
 *  -Refactored get_new_mmu_context( ) to only handle live-mm.
 *   retiring-mm handled in other hooks
 *
 * Vineetg: March 25th, 2008: Bug #92690
 *  -Major rewrite of Core ASID allocation routine get_new_mmu_context
 *
 * Amit Bhor, Sameer Dhavale: Codito Technologies 2004
 */

#ifndef _ASM_ARC_MMU_CONTEXT_H
#define _ASM_ARC_MMU_CONTEXT_H

#include <asm/arcregs.h>
#include <asm/tlb.h>
#include <linux/sched/mm.h>

#include <asm-generic/mm_hooks.h>

/*		ARC700 ASID Management
 *
 * ARC MMU provides 8-bit ASID (0..255) to TAG TLB entries, allowing entries
 * with same vaddr (different tasks) to co-exit. This provides for
 * "Fast Context Switch" i.e. no TLB flush on ctxt-switch
 *
 * Linux assigns each task a unique ASID. A simple round-robin allocation
 * of H/w ASID is done using software tracker @asid_cpu.
 * When it reaches max 255, the allocation cycle starts afresh by flushing
 * the entire TLB and wrapping ASID back to zero.
 *
 * A new allocation cycle, post rollover, could potentially reassign an ASID
 * to a different task. Thus the rule is to refresh the ASID in a new cycle.
 * The 32 bit @asid_cpu (and mm->asid) have 8 bits MMU PID and rest 24 bits
 * serve as cycle/generation indicator and natural 32 bit unsigned math
 * automagically increments the generation when lower 8 bits rollover.
 */

#define MM_CTXT_ASID_MASK	0x000000ff /* MMU PID reg :8 bit PID */
#define MM_CTXT_CYCLE_MASK	(~MM_CTXT_ASID_MASK)

#define MM_CTXT_FIRST_CYCLE	(MM_CTXT_ASID_MASK + 1)
#define MM_CTXT_NO_ASID		0UL

#define asid_mm(mm, cpu)	mm->context.asid[cpu]
#define hw_pid(mm, cpu)		(asid_mm(mm, cpu) & MM_CTXT_ASID_MASK)

DECLARE_PER_CPU(unsigned int, asid_cache);
#define asid_cpu(cpu)		per_cpu(asid_cache, cpu)

/*
 * Get a new ASID if task doesn't have a valid one (unalloc or from prev cycle)
 * Also set the MMU PID register to existing/updated ASID
 */
static inline void get_new_mmu_context(struct mm_struct *mm)
{
	const unsigned int cpu = smp_processor_id();
	unsigned long flags;

	local_irq_save(flags);

	/*
	 * Move to new ASID if it was not from current alloc-cycle/generation.
	 * This is done by ensuring that the generation bits in both mm->ASID
	 * and cpu's ASID counter are exactly same.
	 *
	 * Note: Callers needing new ASID unconditionally, independent of
	 * 	 generation, e.g. local_flush_tlb_mm() for forking  parent,
	 * 	 first need to destroy the context, setting it to invalid
	 * 	 value.
	 */
	if (!((asid_mm(mm, cpu) ^ asid_cpu(cpu)) & MM_CTXT_CYCLE_MASK))
		goto set_hw;

	/* move to new ASID and handle rollover */
	if (unlikely(!(++asid_cpu(cpu) & MM_CTXT_ASID_MASK))) {

		local_flush_tlb_all();

		/*
		 * Above check for rollover of 8 bit ASID in 32 bit container.
		 * If the container itself wrapped around, set it to a non zero
		 * "generation" to distinguish from no context
		 */
		if (!asid_cpu(cpu))
			asid_cpu(cpu) = MM_CTXT_FIRST_CYCLE;
	}

	/* Assign new ASID to tsk */
	asid_mm(mm, cpu) = asid_cpu(cpu);

set_hw:
	write_aux_reg(ARC_REG_PID, hw_pid(mm, cpu) | MMU_ENABLE);

	local_irq_restore(flags);
}

/*
 * Initialize the context related info for a new mm_struct
 * instance.
 */
static inline int
init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
	int i;

	for_each_possible_cpu(i)
		asid_mm(mm, i) = MM_CTXT_NO_ASID;

	return 0;
}

static inline void destroy_context(struct mm_struct *mm)
{
	unsigned long flags;

	/* Needed to elide CONFIG_DEBUG_PREEMPT warning */
	local_irq_save(flags);
	asid_mm(mm, smp_processor_id()) = MM_CTXT_NO_ASID;
	local_irq_restore(flags);
}

/* Prepare the MMU for task: setup PID reg with allocated ASID
    If task doesn't have an ASID (never alloc or stolen, get a new ASID)
*/
static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
			     struct task_struct *tsk)
{
	const int cpu = smp_processor_id();

	/*
	 * Note that the mm_cpumask is "aggregating" only, we don't clear it
	 * for the switched-out task, unlike some other arches.
	 * It is used to enlist cpus for sending TLB flush IPIs and not sending
	 * it to CPUs where a task once ran-on, could cause stale TLB entry
	 * re-use, specially for a multi-threaded task.
	 * e.g. T1 runs on C1, migrates to C3. T2 running on C2 munmaps.
	 *      For a non-aggregating mm_cpumask, IPI not sent C1, and if T1
	 *      were to re-migrate to C1, it could access the unmapped region
	 *      via any existing stale TLB entries.
	 */
	cpumask_set_cpu(cpu, mm_cpumask(next));

#ifndef CONFIG_SMP
	/* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */
	write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
#endif

	get_new_mmu_context(next);
}

/*
 * Called at the time of execve() to get a new ASID
 * Note the subtlety here: get_new_mmu_context() behaves differently here
 * vs. in switch_mm(). Here it always returns a new ASID, because mm has
 * an unallocated "initial" value, while in latter, it moves to a new ASID,
 * only if it was unallocated
 */
#define activate_mm(prev, next)		switch_mm(prev, next, NULL)

/* it seemed that deactivate_mm( ) is a reasonable place to do book-keeping
 * for retiring-mm. However destroy_context( ) still needs to do that because
 * between mm_release( ) = >deactive_mm( ) and
 * mmput => .. => __mmdrop( ) => destroy_context( )
 * there is a good chance that task gets sched-out/in, making it's ASID valid
 * again (this teased me for a whole day).
 */
#define deactivate_mm(tsk, mm)   do { } while (0)

#define enter_lazy_tlb(mm, tsk)

#endif /* __ASM_ARC_MMU_CONTEXT_H */