| /* |
| * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License version 2 as |
| * published by the Free Software Foundation. |
| * |
| * 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 <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_cache. |
| * When it reaches max 255, the allocation cycle starts afresh by flushing |
| * the entire TLB and wrapping ASID back to zero. |
| * |
| * For book-keeping, Linux uses a couple of data-structures: |
| * -mm_struct has an @asid field to keep a note of task's ASID (needed at the |
| * time of say switch_mm( ) |
| * -An array of mm structs @asid_mm_map[] for asid->mm the reverse mapping, |
| * given an ASID, finding the mm struct associated. |
| * |
| * The round-robin allocation algorithm allows for ASID stealing. |
| * If asid tracker is at "x-1", a new req will allocate "x", even if "x" was |
| * already assigned to another (switched-out) task. Obviously the prev owner |
| * is marked with an invalid ASID to make it request for a new ASID when it |
| * gets scheduled next time. However its TLB entries (with ASID "x") could |
| * exist, which must be cleared before the same ASID is used by the new owner. |
| * Flushing them would be plausible but costly solution. Instead we force a |
| * allocation policy quirk, which ensures that a stolen ASID won't have any |
| * TLB entries associates, alleviating the need to flush. |
| * The quirk essentially is not allowing ASID allocated in prev cycle |
| * to be used past a roll-over in the next cycle. |
| * When this happens (i.e. task ASID > asid tracker), task needs to refresh |
| * its ASID, aligning it to current value of tracker. If the task doesn't get |
| * scheduled past a roll-over, hence its ASID is not yet realigned with |
| * tracker, such ASID is anyways safely reusable because it is |
| * gauranteed that TLB entries with that ASID wont exist. |
| */ |
| |
| #define FIRST_ASID 0 |
| #define MAX_ASID 255 /* 8 bit PID field in PID Aux reg */ |
| #define NO_ASID (MAX_ASID + 1) /* ASID Not alloc to mmu ctxt */ |
| #define NUM_ASID ((MAX_ASID - FIRST_ASID) + 1) |
| |
| /* ASID to mm struct mapping */ |
| extern struct mm_struct *asid_mm_map[NUM_ASID + 1]; |
| |
| extern int asid_cache; |
| |
| /* |
| * 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) |
| { |
| struct mm_struct *prev_owner; |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| |
| /* |
| * Move to new ASID if it was not from current alloc-cycle/generation. |
| * |
| * 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 (mm->context.asid <= asid_cache) |
| goto set_hw; |
| |
| /* |
| * Relinquish the currently owned ASID (if any). |
| * Doing unconditionally saves a cmp-n-branch; for already unused |
| * ASID slot, the value was/remains NULL |
| */ |
| asid_mm_map[mm->context.asid] = (struct mm_struct *)NULL; |
| |
| /* move to new ASID */ |
| if (++asid_cache > MAX_ASID) { /* ASID roll-over */ |
| asid_cache = FIRST_ASID; |
| flush_tlb_all(); |
| } |
| |
| /* |
| * Is next ASID already owned by some-one else (we are stealing it). |
| * If so, let the orig owner be aware of this, so when it runs, it |
| * asks for a brand new ASID. This would only happen for a long-lived |
| * task with ASID from prev allocation cycle (before ASID roll-over). |
| * |
| * This might look wrong - if we are re-using some other task's ASID, |
| * won't we use it's stale TLB entries too. Actually the algorithm takes |
| * care of such a case: it ensures that task with ASID from prev alloc |
| * cycle, when scheduled will refresh it's ASID |
| * The stealing scenario described here will only happen if that task |
| * didn't get a chance to refresh it's ASID - implying stale entries |
| * won't exist. |
| */ |
| prev_owner = asid_mm_map[asid_cache]; |
| if (prev_owner) |
| prev_owner->context.asid = NO_ASID; |
| |
| /* Assign new ASID to tsk */ |
| asid_mm_map[asid_cache] = mm; |
| mm->context.asid = asid_cache; |
| |
| set_hw: |
| write_aux_reg(ARC_REG_PID, mm->context.asid | 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) |
| { |
| mm->context.asid = NO_ASID; |
| return 0; |
| } |
| |
| /* 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) |
| { |
| #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) |
| |
| static inline void destroy_context(struct mm_struct *mm) |
| { |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| |
| asid_mm_map[mm->context.asid] = NULL; |
| mm->context.asid = NO_ASID; |
| |
| local_irq_restore(flags); |
| } |
| |
| /* 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 */ |