linux-kernel - [RFC PATCH v2 0/3] mm/gup: fix gup_fast with dynamic page table folding

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Date:   Mon,  7 Sep 2020 20:00:55 +0200
From:   Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, John Hubbard <jhubbard@...dia.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Russell King <linux@...linux.org.uk>,
        Mike Rapoport <rppt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        linux-x86 <x86@...nel.org>,
        linux-arm <linux-arm-kernel@...ts.infradead.org>,
        linux-power <linuxppc-dev@...ts.ozlabs.org>,
        linux-sparc <sparclinux@...r.kernel.org>,
        linux-um <linux-um@...ts.infradead.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Subject: [RFC PATCH v2 0/3] mm/gup: fix gup_fast with dynamic page table folding

This is v2 of an RFC previously discussed here:
https://lore.kernel.org/lkml/20200828140314.8556-1-gerald.schaefer@linux.ibm.com/

Patch 1 is a fix for a regression in gup_fast on s390, after our conversion
to common gup_fast code. It will introduce special helper functions
pXd_addr_end_folded(), which have to be used in places where pagetable walk
is done w/o lock and with READ_ONCE, so currently only in gup_fast.

Patch 2 is an attempt to make that more generic, i.e. change pXd_addr_end()
themselves by adding an extra pXd value parameter. That was suggested by
Jason during v1 discussion, because he is already thinking of some other
places where he might want to switch to the READ_ONCE logic for pagetable
walks. In general, that would be the cleanest / safest solution, but there
is some impact on other architectures and common code, hence the new and
greatly enlarged recipient list.

Patch 3 is a "nice to have" add-on, which makes pXd_addr_end() inline
functions instead of #defines, so that we get some type checking for the
new pXd value parameter.

Not sure about Fixes/stable tags for the generic solution. Only patch 1
fixes a real bug on s390, and has Fixes/stable tags. Patches 2 + 3 might
still be nice to have in stable, to ease future backports, but I guess
"nice to have" does not really qualify for stable backports.

Changes in v2:
- Pick option 2 from v1 discussion (pXd_addr_end_folded helpers)
- Add patch 2 + 3 for more generic approach

Alexander Gordeev (3):
  mm/gup: fix gup_fast with dynamic page table folding
  mm: make pXd_addr_end() functions page-table entry aware
  mm: make generic pXd_addr_end() macros inline functions

 arch/arm/include/asm/pgtable-2level.h    |  2 +-
 arch/arm/mm/idmap.c                      |  6 ++--
 arch/arm/mm/mmu.c                        |  8 ++---
 arch/arm64/kernel/hibernate.c            | 16 +++++----
 arch/arm64/kvm/mmu.c                     | 16 ++++-----
 arch/arm64/mm/kasan_init.c               |  8 ++---
 arch/arm64/mm/mmu.c                      | 25 +++++++-------
 arch/powerpc/mm/book3s64/radix_pgtable.c |  7 ++--
 arch/powerpc/mm/hugetlbpage.c            |  6 ++--
 arch/s390/include/asm/pgtable.h          | 42 ++++++++++++++++++++++++
 arch/s390/mm/page-states.c               |  8 ++---
 arch/s390/mm/pageattr.c                  |  8 ++---
 arch/s390/mm/vmem.c                      |  8 ++---
 arch/sparc/mm/hugetlbpage.c              |  6 ++--
 arch/um/kernel/tlb.c                     |  8 ++---
 arch/x86/mm/init_64.c                    | 15 ++++-----
 arch/x86/mm/kasan_init_64.c              | 16 ++++-----
 include/asm-generic/pgtable-nop4d.h      |  2 +-
 include/asm-generic/pgtable-nopmd.h      |  2 +-
 include/asm-generic/pgtable-nopud.h      |  2 +-
 include/linux/pgtable.h                  | 38 ++++++++++++---------
 mm/gup.c                                 |  8 ++---
 mm/ioremap.c                             |  8 ++---
 mm/kasan/init.c                          | 17 +++++-----
 mm/madvise.c                             |  4 +--
 mm/memory.c                              | 40 +++++++++++-----------
 mm/mlock.c                               | 18 +++++++---
 mm/mprotect.c                            |  8 ++---
 mm/pagewalk.c                            |  8 ++---
 mm/swapfile.c                            |  8 ++---
 mm/vmalloc.c                             | 16 ++++-----
 31 files changed, 219 insertions(+), 165 deletions(-)

-- 
2.17.1