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/* SPDX-License-Identifier: GPL-2.0-only */
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (
* 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
#include <linux/sched/mm.h>
#include <asm/tlb.h>
#include <asm-generic/mm_hooks.h>
/* ARC ASID Management
* MMU tags TLBs with an 8-bit ASID, avoiding need to flush the TLB on
* context-switch.
* ASID is managed per cpu, so task threads across CPUs can have different
* ASID. Global ASID management is needed if hardware supports TLB shootdown
* and/or shared TLB across cores, which ARC doesn't.
* Each task is assigned unique ASID, with a simple round-robin allocator
* tracked in @asid_cpu. When 8-bit value rolls over,a new cycle is started
* over from 0, and TLB is flushed
* 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 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;
* 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))) {
* 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);
mmu_setup_asid(mm, hw_pid(mm, cpu));
* Initialize the context related info for a new mm_struct
* instance.
#define init_new_context init_new_context
static inline int
init_new_context(struct task_struct *tsk, struct mm_struct *mm)
int i;
asid_mm(mm, i) = MM_CTXT_NO_ASID;
return 0;
#define destroy_context destroy_context
static inline void destroy_context(struct mm_struct *mm)
unsigned long flags;
/* Needed to elide CONFIG_DEBUG_PREEMPT warning */
asid_mm(mm, smp_processor_id()) = MM_CTXT_NO_ASID;
/* 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));
mmu_setup_pgd(next, next->pgd);
* activate_mm defaults (in asm-generic) to switch_mm and is 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
/* 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).
#include <asm-generic/mmu_context.h>
#endif /* __ASM_ARC_MMU_CONTEXT_H */