linux-kernel - [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow

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Date:   Thu, 27 Jul 2023 23:28:41 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        liubo <liubo254@...wei.com>, Peter Xu <peterx@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>
Subject: [PATCH v1 0/4]  smaps / mm/gup: fix gup_can_follow_protnone fallout

This is my proposal on how to handle the fallout of 474098edac26
("mm/gup: replace FOLL_NUMA by gup_can_follow_protnone()") where I
accidentially missed that follow_page() and smaps implicitly kept the
FOLL_NUMA flag clear by *not* setting it if FOLL_FORCE is absent, to
not trigger faults on PROT_NONE-mapped PTEs.

(maybe it's just me who considers that confusing)

Patch #1 is the original fix proposal, which patch #3 cleans up. Patch #2
is another fix for the issue on the follow_page() level pointed out by
Peter. Patch #4 documents the FOLL_FORCE situation.

Peter prefers a revert of that commit [1], I disagree and am still happy to
see FOLL_NUMA gone that implicitly relied on FOLL_FORCE.

An alternative might be to use an internal FOLL_PROTNONE or
FOLL_NO_PROTNONE flag in patch #3, not so sure about that.

Did a quick sanity test, will do more testing tomorrow.

[1] https://lkml.kernel.org/r/ZMK+jSDgOmJKySTr@x1n

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: liubo <liubo254@...wei.com>
Cc: Peter Xu <peterx@...hat.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: John Hubbard <jhubbard@...dia.com>

David Hildenbrand (3):
  mm/gup: Make follow_page() succeed again on PROT_NONE PTEs/PMDs
  smaps: use vm_normal_page_pmd() instead of follow_trans_huge_pmd()
  mm/gup: document FOLL_FORCE behavior

liubo (1):
  smaps: Fix the abnormal memory statistics obtained through
    /proc/pid/smaps

 fs/proc/task_mmu.c       |  3 +--
 include/linux/mm_types.h | 25 ++++++++++++++++++++++++-
 mm/gup.c                 | 10 +++++++++-
 3 files changed, 34 insertions(+), 4 deletions(-)

-- 
2.41.0