arm64: switch_mm: simplify mm and CPU checks

switch_mm performs some checks to try and avoid entering the ASID
allocator:

  (1) If we're switching to the init_mm (no user mappings), then simply
      set a reserved TTBR0 value with no page table (the zero page)

  (2) If prev == next *and* the mm_cpumask indicates that we've run on
      this CPU before, then we can skip the allocator.

However, there is plenty of redundancy here. With the new ASID allocator,
if prev == next, then we know that our ASID is valid and do not need to
worry about re-allocation. Consequently, we can drop the mm_cpumask check
in (2) and move the prev == next check before the init_mm check, since
if prev == next == init_mm then there's nothing to do.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index e902229b1a3d..4b9ec4484e3f 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -166,10 +166,10 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu)
 		local_flush_tlb_all();
 
 	atomic64_set(&per_cpu(active_asids, cpu), asid);
-	cpumask_set_cpu(cpu, mm_cpumask(mm));
 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
 
 switch_mm_fastpath:
+	cpumask_set_cpu(cpu, mm_cpumask(mm));
 	cpu_switch_mm(mm->pgd, mm);
 }