3daa48d1d9
ASID allocation changes/1
This patch does 2 things:
(1) get_new_mmu_context() NOW moves mm->ASID to a new value ONLY if it
was from a prev allocation cycle/generation OR if mm had no ASID
allocated (vs. before would unconditionally moving to a new ASID)
Callers desiring unconditional update of ASID, e.g.local_flush_tlb_mm()
(for parent's address space invalidation at fork) need to first force
the parent to an unallocated ASID.
(2) get_new_mmu_context() always sets the MMU PID reg with unchanged/new
ASID value.
The gains are:
- consolidation of all asid alloc logic into get_new_mmu_context()
- avoiding code duplication in switch_mm() for PID reg setting
- Enables future change to fold activate_mm() into switch_mm()
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
194 lines
6.4 KiB
C
194 lines
6.4 KiB
C
/*
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* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* vineetg: May 2011
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* -Refactored get_new_mmu_context( ) to only handle live-mm.
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* retiring-mm handled in other hooks
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*
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* Vineetg: March 25th, 2008: Bug #92690
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* -Major rewrite of Core ASID allocation routine get_new_mmu_context
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*
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* Amit Bhor, Sameer Dhavale: Codito Technologies 2004
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*/
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#ifndef _ASM_ARC_MMU_CONTEXT_H
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#define _ASM_ARC_MMU_CONTEXT_H
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#include <asm/arcregs.h>
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#include <asm/tlb.h>
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#include <asm-generic/mm_hooks.h>
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/* ARC700 ASID Management
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*
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* ARC MMU provides 8-bit ASID (0..255) to TAG TLB entries, allowing entries
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* with same vaddr (different tasks) to co-exit. This provides for
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* "Fast Context Switch" i.e. no TLB flush on ctxt-switch
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*
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* Linux assigns each task a unique ASID. A simple round-robin allocation
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* of H/w ASID is done using software tracker @asid_cache.
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* When it reaches max 255, the allocation cycle starts afresh by flushing
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* the entire TLB and wrapping ASID back to zero.
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*
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* For book-keeping, Linux uses a couple of data-structures:
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* -mm_struct has an @asid field to keep a note of task's ASID (needed at the
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* time of say switch_mm( )
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* -An array of mm structs @asid_mm_map[] for asid->mm the reverse mapping,
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* given an ASID, finding the mm struct associated.
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*
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* The round-robin allocation algorithm allows for ASID stealing.
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* If asid tracker is at "x-1", a new req will allocate "x", even if "x" was
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* already assigned to another (switched-out) task. Obviously the prev owner
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* is marked with an invalid ASID to make it request for a new ASID when it
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* gets scheduled next time. However its TLB entries (with ASID "x") could
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* exist, which must be cleared before the same ASID is used by the new owner.
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* Flushing them would be plausible but costly solution. Instead we force a
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* allocation policy quirk, which ensures that a stolen ASID won't have any
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* TLB entries associates, alleviating the need to flush.
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* The quirk essentially is not allowing ASID allocated in prev cycle
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* to be used past a roll-over in the next cycle.
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* When this happens (i.e. task ASID > asid tracker), task needs to refresh
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* its ASID, aligning it to current value of tracker. If the task doesn't get
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* scheduled past a roll-over, hence its ASID is not yet realigned with
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* tracker, such ASID is anyways safely reusable because it is
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* gauranteed that TLB entries with that ASID wont exist.
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*/
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#define FIRST_ASID 0
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#define MAX_ASID 255 /* 8 bit PID field in PID Aux reg */
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#define NO_ASID (MAX_ASID + 1) /* ASID Not alloc to mmu ctxt */
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#define NUM_ASID ((MAX_ASID - FIRST_ASID) + 1)
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/* ASID to mm struct mapping */
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extern struct mm_struct *asid_mm_map[NUM_ASID + 1];
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extern int asid_cache;
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/*
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* Get a new ASID if task doesn't have a valid one (unalloc or from prev cycle)
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* Also set the MMU PID register to existing/updated ASID
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*/
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static inline void get_new_mmu_context(struct mm_struct *mm)
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{
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struct mm_struct *prev_owner;
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unsigned long flags;
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local_irq_save(flags);
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/*
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* Move to new ASID if it was not from current alloc-cycle/generation.
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*
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* Note: Callers needing new ASID unconditionally, independent of
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* generation, e.g. local_flush_tlb_mm() for forking parent,
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* first need to destroy the context, setting it to invalid
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* value.
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*/
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if (mm->context.asid <= asid_cache)
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goto set_hw;
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/*
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* Relinquish the currently owned ASID (if any).
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* Doing unconditionally saves a cmp-n-branch; for already unused
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* ASID slot, the value was/remains NULL
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*/
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asid_mm_map[mm->context.asid] = (struct mm_struct *)NULL;
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/* move to new ASID */
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if (++asid_cache > MAX_ASID) { /* ASID roll-over */
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asid_cache = FIRST_ASID;
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flush_tlb_all();
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}
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/*
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* Is next ASID already owned by some-one else (we are stealing it).
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* If so, let the orig owner be aware of this, so when it runs, it
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* asks for a brand new ASID. This would only happen for a long-lived
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* task with ASID from prev allocation cycle (before ASID roll-over).
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*
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* This might look wrong - if we are re-using some other task's ASID,
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* won't we use it's stale TLB entries too. Actually the algorithm takes
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* care of such a case: it ensures that task with ASID from prev alloc
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* cycle, when scheduled will refresh it's ASID
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* The stealing scenario described here will only happen if that task
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* didn't get a chance to refresh it's ASID - implying stale entries
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* won't exist.
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*/
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prev_owner = asid_mm_map[asid_cache];
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if (prev_owner)
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prev_owner->context.asid = NO_ASID;
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/* Assign new ASID to tsk */
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asid_mm_map[asid_cache] = mm;
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mm->context.asid = asid_cache;
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set_hw:
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write_aux_reg(ARC_REG_PID, mm->context.asid | MMU_ENABLE);
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local_irq_restore(flags);
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}
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/*
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* Initialize the context related info for a new mm_struct
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* instance.
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*/
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static inline int
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init_new_context(struct task_struct *tsk, struct mm_struct *mm)
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{
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mm->context.asid = NO_ASID;
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return 0;
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}
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/* Prepare the MMU for task: setup PID reg with allocated ASID
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If task doesn't have an ASID (never alloc or stolen, get a new ASID)
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*/
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static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
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struct task_struct *tsk)
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{
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#ifndef CONFIG_SMP
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/* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */
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write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
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#endif
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get_new_mmu_context(next);
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}
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static inline void destroy_context(struct mm_struct *mm)
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{
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unsigned long flags;
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local_irq_save(flags);
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asid_mm_map[mm->context.asid] = NULL;
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mm->context.asid = NO_ASID;
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local_irq_restore(flags);
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}
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/* it seemed that deactivate_mm( ) is a reasonable place to do book-keeping
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* for retiring-mm. However destroy_context( ) still needs to do that because
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* between mm_release( ) = >deactive_mm( ) and
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* mmput => .. => __mmdrop( ) => destroy_context( )
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* there is a good chance that task gets sched-out/in, making it's ASID valid
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* again (this teased me for a whole day).
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*/
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#define deactivate_mm(tsk, mm) do { } while (0)
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static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)
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{
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#ifndef CONFIG_SMP
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write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
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#endif
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/* Unconditionally get a new ASID */
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get_new_mmu_context(next);
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}
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#define enter_lazy_tlb(mm, tsk)
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#endif /* __ASM_ARC_MMU_CONTEXT_H */
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