337 строки
9.1 KiB
C
337 строки
9.1 KiB
C
/*
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* This file contains the routines for handling the MMU on those
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* PowerPC implementations where the MMU is not using the hash
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* table, such as 8xx, 4xx, BookE's etc...
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*
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* Copyright 2008 Ben Herrenschmidt <benh@kernel.crashing.org>
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* IBM Corp.
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*
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* Derived from previous arch/powerpc/mm/mmu_context.c
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* and arch/powerpc/include/asm/mmu_context.h
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* TODO:
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*
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* - The global context lock will not scale very well
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* - The maps should be dynamically allocated to allow for processors
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* that support more PID bits at runtime
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* - Implement flush_tlb_mm() by making the context stale and picking
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* a new one
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* - More aggressively clear stale map bits and maybe find some way to
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* also clear mm->cpu_vm_mask bits when processes are migrated
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*/
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#undef DEBUG
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#define DEBUG_STEAL_ONLY
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#undef DEBUG_MAP_CONSISTENCY
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/init.h>
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#include <asm/mmu_context.h>
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#include <asm/tlbflush.h>
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#include <linux/spinlock.h>
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/*
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* The MPC8xx has only 16 contexts. We rotate through them on each
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* task switch. A better way would be to keep track of tasks that
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* own contexts, and implement an LRU usage. That way very active
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* tasks don't always have to pay the TLB reload overhead. The
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* kernel pages are mapped shared, so the kernel can run on behalf
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* of any task that makes a kernel entry. Shared does not mean they
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* are not protected, just that the ASID comparison is not performed.
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* -- Dan
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*
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* The IBM4xx has 256 contexts, so we can just rotate through these
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* as a way of "switching" contexts. If the TID of the TLB is zero,
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* the PID/TID comparison is disabled, so we can use a TID of zero
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* to represent all kernel pages as shared among all contexts.
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* -- Dan
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*/
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#ifdef CONFIG_8xx
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#define LAST_CONTEXT 15
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#define FIRST_CONTEXT 0
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#elif defined(CONFIG_4xx)
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#define LAST_CONTEXT 255
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#define FIRST_CONTEXT 1
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#elif defined(CONFIG_E200) || defined(CONFIG_E500)
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#define LAST_CONTEXT 255
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#define FIRST_CONTEXT 1
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#else
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#error Unsupported processor type
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#endif
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static unsigned int next_context, nr_free_contexts;
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static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
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static unsigned long stale_map[NR_CPUS][LAST_CONTEXT / BITS_PER_LONG + 1];
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static struct mm_struct *context_mm[LAST_CONTEXT+1];
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static spinlock_t context_lock = SPIN_LOCK_UNLOCKED;
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/* Steal a context from a task that has one at the moment.
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*
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* This is used when we are running out of available PID numbers
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* on the processors.
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*
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* This isn't an LRU system, it just frees up each context in
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* turn (sort-of pseudo-random replacement :). This would be the
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* place to implement an LRU scheme if anyone was motivated to do it.
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* -- paulus
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*
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* For context stealing, we use a slightly different approach for
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* SMP and UP. Basically, the UP one is simpler and doesn't use
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* the stale map as we can just flush the local CPU
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* -- benh
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*/
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#ifdef CONFIG_SMP
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static unsigned int steal_context_smp(unsigned int id)
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{
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struct mm_struct *mm;
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unsigned int cpu, max;
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again:
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max = LAST_CONTEXT - FIRST_CONTEXT;
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/* Attempt to free next_context first and then loop until we manage */
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while (max--) {
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/* Pick up the victim mm */
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mm = context_mm[id];
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/* We have a candidate victim, check if it's active, on SMP
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* we cannot steal active contexts
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*/
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if (mm->context.active) {
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id++;
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if (id > LAST_CONTEXT)
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id = FIRST_CONTEXT;
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continue;
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}
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pr_debug("[%d] steal context %d from mm @%p\n",
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smp_processor_id(), id, mm);
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/* Mark this mm has having no context anymore */
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mm->context.id = MMU_NO_CONTEXT;
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/* Mark it stale on all CPUs that used this mm */
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for_each_cpu_mask_nr(cpu, mm->cpu_vm_mask)
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__set_bit(id, stale_map[cpu]);
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return id;
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}
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/* This will happen if you have more CPUs than available contexts,
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* all we can do here is wait a bit and try again
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*/
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spin_unlock(&context_lock);
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cpu_relax();
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spin_lock(&context_lock);
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goto again;
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}
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#endif /* CONFIG_SMP */
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/* Note that this will also be called on SMP if all other CPUs are
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* offlined, which means that it may be called for cpu != 0. For
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* this to work, we somewhat assume that CPUs that are onlined
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* come up with a fully clean TLB (or are cleaned when offlined)
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*/
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static unsigned int steal_context_up(unsigned int id)
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{
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struct mm_struct *mm;
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int cpu = smp_processor_id();
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/* Pick up the victim mm */
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mm = context_mm[id];
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pr_debug("[%d] steal context %d from mm @%p\n", cpu, id, mm);
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/* Mark this mm has having no context anymore */
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mm->context.id = MMU_NO_CONTEXT;
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/* Flush the TLB for that context */
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local_flush_tlb_mm(mm);
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/* XXX This clear should ultimately be part of local_flush_tlb_mm */
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__clear_bit(id, stale_map[cpu]);
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return id;
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}
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#ifdef DEBUG_MAP_CONSISTENCY
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static void context_check_map(void)
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{
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unsigned int id, nrf, nact;
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nrf = nact = 0;
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for (id = FIRST_CONTEXT; id <= LAST_CONTEXT; id++) {
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int used = test_bit(id, context_map);
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if (!used)
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nrf++;
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if (used != (context_mm[id] != NULL))
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pr_err("MMU: Context %d is %s and MM is %p !\n",
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id, used ? "used" : "free", context_mm[id]);
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if (context_mm[id] != NULL)
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nact += context_mm[id]->context.active;
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}
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if (nrf != nr_free_contexts) {
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pr_err("MMU: Free context count out of sync ! (%d vs %d)\n",
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nr_free_contexts, nrf);
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nr_free_contexts = nrf;
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}
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if (nact > num_online_cpus())
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pr_err("MMU: More active contexts than CPUs ! (%d vs %d)\n",
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nact, num_online_cpus());
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}
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#else
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static void context_check_map(void) { }
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#endif
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void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
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{
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unsigned int id, cpu = smp_processor_id();
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unsigned long *map;
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/* No lockless fast path .. yet */
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spin_lock(&context_lock);
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#ifndef DEBUG_STEAL_ONLY
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pr_debug("[%d] activating context for mm @%p, active=%d, id=%d\n",
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cpu, next, next->context.active, next->context.id);
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#endif
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#ifdef CONFIG_SMP
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/* Mark us active and the previous one not anymore */
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next->context.active++;
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if (prev) {
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WARN_ON(prev->context.active < 1);
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prev->context.active--;
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}
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#endif /* CONFIG_SMP */
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/* If we already have a valid assigned context, skip all that */
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id = next->context.id;
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if (likely(id != MMU_NO_CONTEXT))
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goto ctxt_ok;
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/* We really don't have a context, let's try to acquire one */
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id = next_context;
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if (id > LAST_CONTEXT)
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id = FIRST_CONTEXT;
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map = context_map;
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/* No more free contexts, let's try to steal one */
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if (nr_free_contexts == 0) {
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#ifdef CONFIG_SMP
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if (num_online_cpus() > 1) {
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id = steal_context_smp(id);
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goto stolen;
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}
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#endif /* CONFIG_SMP */
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id = steal_context_up(id);
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goto stolen;
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}
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nr_free_contexts--;
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/* We know there's at least one free context, try to find it */
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while (__test_and_set_bit(id, map)) {
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id = find_next_zero_bit(map, LAST_CONTEXT+1, id);
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if (id > LAST_CONTEXT)
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id = FIRST_CONTEXT;
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}
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stolen:
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next_context = id + 1;
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context_mm[id] = next;
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next->context.id = id;
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#ifndef DEBUG_STEAL_ONLY
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pr_debug("[%d] picked up new id %d, nrf is now %d\n",
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cpu, id, nr_free_contexts);
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#endif
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context_check_map();
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ctxt_ok:
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/* If that context got marked stale on this CPU, then flush the
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* local TLB for it and unmark it before we use it
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*/
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if (test_bit(id, stale_map[cpu])) {
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pr_debug("[%d] flushing stale context %d for mm @%p !\n",
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cpu, id, next);
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local_flush_tlb_mm(next);
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/* XXX This clear should ultimately be part of local_flush_tlb_mm */
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__clear_bit(id, stale_map[cpu]);
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}
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/* Flick the MMU and release lock */
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set_context(id, next->pgd);
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spin_unlock(&context_lock);
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}
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/*
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* Set up the context for a new address space.
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*/
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int init_new_context(struct task_struct *t, struct mm_struct *mm)
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{
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mm->context.id = MMU_NO_CONTEXT;
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mm->context.active = 0;
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return 0;
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}
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/*
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* We're finished using the context for an address space.
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*/
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void destroy_context(struct mm_struct *mm)
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{
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unsigned int id;
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if (mm->context.id == MMU_NO_CONTEXT)
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return;
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WARN_ON(mm->context.active != 0);
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spin_lock(&context_lock);
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id = mm->context.id;
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if (id != MMU_NO_CONTEXT) {
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__clear_bit(id, context_map);
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mm->context.id = MMU_NO_CONTEXT;
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#ifdef DEBUG_MAP_CONSISTENCY
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mm->context.active = 0;
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context_mm[id] = NULL;
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#endif
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nr_free_contexts++;
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}
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spin_unlock(&context_lock);
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}
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/*
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* Initialize the context management stuff.
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*/
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void __init mmu_context_init(void)
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{
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/* Mark init_mm as being active on all possible CPUs since
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* we'll get called with prev == init_mm the first time
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* we schedule on a given CPU
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*/
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init_mm.context.active = NR_CPUS;
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/*
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* Some processors have too few contexts to reserve one for
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* init_mm, and require using context 0 for a normal task.
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* Other processors reserve the use of context zero for the kernel.
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* This code assumes FIRST_CONTEXT < 32.
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*/
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context_map[0] = (1 << FIRST_CONTEXT) - 1;
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next_context = FIRST_CONTEXT;
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nr_free_contexts = LAST_CONTEXT - FIRST_CONTEXT + 1;
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}
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