arm64: switch_mm: simplify mm and CPU checksv3.18/topic/mm-kaslr

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>
(cherry picked from commit c2775b2ee5caca19f661ee2ab5af92462596db71)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

0 files changed, 0 insertions, 0 deletions