linux-kernel - [RFC PATCH 0/7] mm: Get rid of vmalloc_sync

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Message-Id: <20200508144043.13893-1-joro@8bytes.org>
Date:   Fri,  8 May 2020 16:40:36 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     hpa@...or.com, Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, rjw@...ysocki.net,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Joerg Roedel <jroedel@...e.de>, joro@...tes.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org
Subject: [RFC PATCH 0/7] mm: Get rid of vmalloc_sync_(un)mappings()

Hi,

after the recent issue with vmalloc and tracing code[1] on x86 and a
long history of previous issues related to the vmalloc_sync_mappings()
interface, I thought the time has come to remove it. Please
see [2], [3], and [4] for some other issues in the past.

The patches are based on v5.7-rc4 and add tracking of page-table
directory changes to the vmalloc and ioremap code. Depending on which
page-table levels changes have been made, a new per-arch function is
called: arch_sync_kernel_mappings().

On x86-64 with 4-level paging, this function will not be called more
than 64 times in a systems runtime (because vmalloc-space takes 64 PGD
entries which are only populated, but never cleared).

As a side effect this also allows to get rid of vmalloc faults on x86,
making it safe to touch vmalloc'ed memory in the page-fault handler.
Note that this potentially includes per-cpu memory.

The code is tested on x86-64, x86-32 with and without PAE. It also fixes
the issue described in [1]. Additionally this code has been
compile-tested on almost all architectures supported by Linux. I
couldn't find working compilers for hexagon and unicore32, so these are
not tested.

Please review.

Regards,

	Joerg

[1] https://lore.kernel.org/lkml/20200430141120.GA8135@suse.de/
[2] https://lore.kernel.org/lkml/20191009124418.8286-1-joro@8bytes.org/
[3] https://lore.kernel.org/lkml/20190719184652.11391-1-joro@8bytes.org/
[4] https://lore.kernel.org/lkml/20191126111119.GA110513@gmail.com/

Joerg Roedel (7):
  mm: Add functions to track page directory modifications
  mm/vmalloc: Track which page-table levels were modified
  mm/ioremap: Track which page-table levels were modified
  x86/mm/64: Implement arch_sync_kernel_mappings()
  x86/mm/32: Implement arch_sync_kernel_mappings()
  mm: Remove vmalloc_sync_(un)mappings()
  x86/mm: Remove vmalloc faulting

 arch/x86/include/asm/pgtable-2level_types.h |   2 +
 arch/x86/include/asm/pgtable-3level_types.h |   2 +
 arch/x86/include/asm/pgtable_64_types.h     |   2 +
 arch/x86/include/asm/switch_to.h            |  23 ---
 arch/x86/kernel/setup_percpu.c              |   6 +-
 arch/x86/mm/fault.c                         | 176 +-------------------
 arch/x86/mm/init_64.c                       |   5 +
 arch/x86/mm/pti.c                           |   8 +-
 drivers/acpi/apei/ghes.c                    |   6 -
 include/asm-generic/5level-fixup.h          |   5 +-
 include/asm-generic/pgtable.h               |  23 +++
 include/linux/mm.h                          |  46 +++++
 include/linux/vmalloc.h                     |  13 +-
 kernel/notifier.c                           |   1 -
 lib/ioremap.c                               |  46 +++--
 mm/nommu.c                                  |  12 --
 mm/vmalloc.c                                | 109 +++++++-----
 17 files changed, 199 insertions(+), 286 deletions(-)

-- 
2.17.1