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authorVineet Gupta <vgupta@synopsys.com>2013-07-24 13:53:45 -0700
committerVineet Gupta <vgupta@synopsys.com>2013-08-30 21:42:18 +0530
commit3daa48d1d9bc44baa079d65e72ef2e3f1139ac03 (patch)
tree2e659049c5ee5584c789cc42643aa653cfdb307d /arch/arc
parent5bd87adf9b2ae5fa1bb469c68029b4eec06d6e03 (diff)
ARC: [ASID] get_new_mmu_context() to conditionally allocate new ASID
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>
Diffstat (limited to 'arch/arc')
-rw-r--r--arch/arc/include/asm/mmu_context.h45
-rw-r--r--arch/arc/mm/tlb.c13
2 files changed, 25 insertions, 33 deletions
diff --git a/arch/arc/include/asm/mmu_context.h b/arch/arc/include/asm/mmu_context.h
index a63800fd1dba..7a3ecd25ffc9 100644
--- a/arch/arc/include/asm/mmu_context.h
+++ b/arch/arc/include/asm/mmu_context.h
@@ -69,8 +69,8 @@ extern struct mm_struct *asid_mm_map[NUM_ASID + 1];
extern int asid_cache;
/*
- * Assign a new ASID to task. If the task already has an ASID, it is
- * relinquished.
+ * 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)
{
@@ -80,6 +80,17 @@ static inline void get_new_mmu_context(struct mm_struct *mm)
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
@@ -99,9 +110,9 @@ static inline void get_new_mmu_context(struct mm_struct *mm)
* 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 switch_mm( ) takes
+ * 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: see switch_mm( ) below
+ * 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.
@@ -114,7 +125,8 @@ static inline void get_new_mmu_context(struct mm_struct *mm)
asid_mm_map[asid_cache] = mm;
mm->context.asid = asid_cache;
- write_aux_reg(ARC_REG_PID, asid_cache | MMU_ENABLE);
+set_hw:
+ write_aux_reg(ARC_REG_PID, mm->context.asid | MMU_ENABLE);
local_irq_restore(flags);
}
@@ -141,28 +153,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
#endif
- /*
- * Get a new ASID if task doesn't have a valid one. Possible when
- * -task never had an ASID (fresh after fork)
- * -it's ASID was stolen - past an ASID roll-over.
- * -There's a third obscure scenario (if this task is running for the
- * first time afer an ASID rollover), where despite having a valid
- * ASID, we force a get for new ASID - see comments at top.
- *
- * Both the non-alloc scenario and first-use-after-rollover can be
- * detected using the single condition below: NO_ASID = 256
- * while asid_cache is always a valid ASID value (0-255).
- */
- if (next->context.asid > asid_cache) {
- get_new_mmu_context(next);
- } else {
- /*
- * XXX: This will never happen given the chks above
- * BUG_ON(next->context.asid > MAX_ASID);
- */
- write_aux_reg(ARC_REG_PID, next->context.asid | MMU_ENABLE);
- }
-
+ get_new_mmu_context(next);
}
static inline void destroy_context(struct mm_struct *mm)
diff --git a/arch/arc/mm/tlb.c b/arch/arc/mm/tlb.c
index a4ad68c4b50d..b5c5e0aa0aaa 100644
--- a/arch/arc/mm/tlb.c
+++ b/arch/arc/mm/tlb.c
@@ -258,13 +258,14 @@ noinline void local_flush_tlb_mm(struct mm_struct *mm)
return;
/*
- * Workaround for Android weirdism:
- * A binder VMA could end up in a task such that vma->mm != tsk->mm
- * old code would cause h/w - s/w ASID to get out of sync
+ * - Move to a new ASID, but only if the mm is still wired in
+ * (Android Binder ended up calling this for vma->mm != tsk->mm,
+ * causing h/w - s/w ASID to get out of sync)
+ * - Also get_new_mmu_context() new implementation allocates a new
+ * ASID only if it is not allocated already - so unallocate first
*/
- if (current->mm != mm)
- destroy_context(mm);
- else
+ destroy_context(mm);
+ if (current->mm == mm)
get_new_mmu_context(mm);
}