linux-kernel - [PATCH v2 0/5] mm/mprotect: avoid unnecessary TLB flushes

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Date:   Thu, 21 Oct 2021 05:21:07 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, Nadav Amit <namit@...are.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Xu <peterx@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Nick Piggin <npiggin@...il.com>, x86@...nel.org
Subject: [PATCH v2 0/5] mm/mprotect: avoid unnecessary TLB flushes

From: Nadav Amit <namit@...are.com>

This patch-set is intended to remove unnecessary TLB flushes. It is
based on feedback from v1 and several bugs I found in v1 myself.

Basically, there are 3 optimizations in this patch-set:
1. Avoiding TLB flushes on change_huge_pmd() that are only needed to
   prevent the A/D bits from changing.
2. Use TLB batching infrastructure to batch flushes across VMAs and
   do better/fewer flushes.
3. Avoid TLB flushes on permission demotion.

Andrea asked for the aforementioned (2) to come after (3), but this
is not simple (specifically since change_prot_numa() needs the number
of pages affected).

There are many changes from v1 to v2 so consider the change log as
partial.

v1->v2:
* Wrong detection of permission demotion [Andrea]
* Better comments [Andrea]
* Handle THP [Andrea]
* Batching across VMAs [Peter Xu]
* Avoid open-coding PTE analysis
* Fix wrong use of the mmu_gather()

Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Peter Xu <peterx@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will@...nel.org>
Cc: Yu Zhao <yuzhao@...gle.com>
Cc: Nick Piggin <npiggin@...il.com>
Cc: x86@...nel.org

Nadav Amit (5):
  x86: Detection of Knights Landing A/D leak
  mm: avoid unnecessary flush on change_huge_pmd()
  x86/mm: check exec permissions on fault
  mm/mprotect: use mmu_gather
  mm/mprotect: do not flush on permission promotion

 arch/x86/include/asm/cpufeatures.h   |  1 +
 arch/x86/include/asm/pgtable.h       |  8 +++
 arch/x86/include/asm/pgtable_types.h |  2 +
 arch/x86/include/asm/tlbflush.h      | 80 +++++++++++++++++++++++
 arch/x86/kernel/cpu/intel.c          |  5 ++
 arch/x86/mm/fault.c                  | 11 +++-
 fs/exec.c                            |  6 +-
 include/asm-generic/tlb.h            | 14 +++++
 include/linux/huge_mm.h              |  5 +-
 include/linux/mm.h                   |  5 +-
 include/linux/pgtable.h              |  5 ++
 mm/huge_memory.c                     | 22 ++++---
 mm/mprotect.c                        | 94 +++++++++++++++-------------
 mm/pgtable-generic.c                 |  8 +++
 mm/userfaultfd.c                     |  6 +-
 15 files changed, 215 insertions(+), 57 deletions(-)

-- 
2.25.1