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Subject: Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table
 entry aware
To: Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
 Jason Gunthorpe <jgg@ziepe.ca>, John Hubbard <jhubbard@nvidia.com>
References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com>
 <20200907180058.64880-3-gerald.schaefer@linux.ibm.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
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Date: Tue, 8 Sep 2020 07:14:38 +0200
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Le 07/09/2020 à 20:00, Gerald Schaefer a écrit :
> From: Alexander Gordeev <agordeev@linux.ibm.com>
> 
> Unlike all other page-table abstractions pXd_addr_end() do not take
> into account a particular table entry in which context the functions
> are called. On architectures with dynamic page-tables folding that
> might lead to lack of necessary information that is difficult to
> obtain other than from the table entry itself. That already led to
> a subtle memory corruption issue on s390.
> 
> By letting pXd_addr_end() functions know about the page-table entry
> we allow archs not only make extra checks, but also optimizations.
> 
> As result of this change the pXd_addr_end_folded() functions used
> in gup_fast traversal code become unnecessary and get replaced with
> universal pXd_addr_end() variants.
> 
> The arch-specific updates not only add dereferencing of page-table
> entry pointers, but also small changes to the code flow to make those
> dereferences possible, at least for x86 and powerpc. Also for arm64,
> but in way that should not have any impact.
> 

[...]

> 
> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
> ---
>   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 ++--

You forgot arch/powerpc/mm/book3s64/subpage_prot.c it seems.

>   arch/s390/include/asm/pgtable.h          |  8 ++---
>   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                  | 26 ++++-----------
>   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, 165 insertions(+), 173 deletions(-)

Christophe