diff options
Diffstat (limited to 'arch/arm64/mm/context.c')
| -rw-r--r-- | arch/arm64/mm/context.c | 28 |
1 files changed, 16 insertions, 12 deletions
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c index ab9f5f0fb2c7..6f4017046323 100644 --- a/arch/arm64/mm/context.c +++ b/arch/arm64/mm/context.c @@ -96,12 +96,6 @@ static void flush_context(unsigned int cpu) set_reserved_asid_bits(); - /* - * Ensure the generation bump is observed before we xchg the - * active_asids. - */ - smp_wmb(); - for_each_possible_cpu(i) { asid = atomic64_xchg_relaxed(&per_cpu(active_asids, i), 0); /* @@ -117,7 +111,10 @@ static void flush_context(unsigned int cpu) per_cpu(reserved_asids, i) = asid; } - /* Queue a TLB invalidate and flush the I-cache if necessary. */ + /* + * Queue a TLB invalidation for each CPU to perform on next + * context-switch + */ cpumask_setall(&tlb_flush_pending); } @@ -202,11 +199,18 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) asid = atomic64_read(&mm->context.id); /* - * The memory ordering here is subtle. We rely on the control - * dependency between the generation read and the update of - * active_asids to ensure that we are synchronised with a - * parallel rollover (i.e. this pairs with the smp_wmb() in - * flush_context). + * The memory ordering here is subtle. + * If our ASID matches the current generation, then we update + * our active_asids entry with a relaxed xchg. Racing with a + * concurrent rollover means that either: + * + * - We get a zero back from the xchg and end up waiting on the + * lock. Taking the lock synchronises with the rollover and so + * we are forced to see the updated generation. + * + * - We get a valid ASID back from the xchg, which means the + * relaxed xchg in flush_context will treat us as reserved + * because atomic RmWs are totally ordered for a given location. */ if (!((asid ^ atomic64_read(&asid_generation)) >> asid_bits) && atomic64_xchg_relaxed(&per_cpu(active_asids, cpu), asid)) |
