arm64/mm: implement new wrprotect_ptes() batch API

Optimize the contpte implementation to fix some of the fork performance
regression introduced by the initial contpte commit.  Subsequent patches
will solve it entirely.

During fork(), any private memory in the parent must be write-protected. 
Previously this was done 1 PTE at a time.  But the core-mm supports
batched wrprotect via the new wrprotect_ptes() API.  So let's implement
that API and for fully covered contpte mappings, we no longer need to
unfold the contpte.  This has 2 benefits:

  - reduced unfolding, reduces the number of tlbis that must be issued.
  - The memory remains contpte-mapped ("folded") in the parent, so it
    continues to benefit from the more efficient use of the TLB after
    the fork.

The optimization to wrprotect a whole contpte block without unfolding is
possible thanks to the tightening of the Arm ARM in respect to the
definition and behaviour when 'Misprogramming the Contiguous bit'.  See
section D21194 at https://developer.arm.com/documentation/102105/ja-07/

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ryan Roberts <[email protected]>
Tested-by: John Hubbard <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Borislav Petkov (AMD) <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Morse <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions