linux-kernel - [PATCH v2 0/5] mm: A few cleanup patches around zap, shmem and uffd

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Date:   Thu,  2 Sep 2021 16:17:16 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Yang Shi <shy828301@...il.com>,
        Matthew Wilcox <willy@...radead.org>, peterx@...hat.com,
        Jerome Glisse <jglisse@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Alistair Popple <apopple@...dia.com>
Subject: [PATCH v2 0/5] mm: A few cleanup patches around zap, shmem and uffd

[Based on tag v5.14, but it should still apply to -mm too.  If not, I can
 repost anytime]

Hugh,

So I found one thing that I feel like a bug of commit 22061a1ffabdb9c3, but I'm
not sure.  If that's the case, patch 5 of this series may be the fix for it.

The problem is unmap_mapping_page() in current tree is calling
unmap_mapping_range_tree() with a details pointer, while by default when detail
pointer is specified, it means "we want to skip zapping swap entries".

I didn't mention this in v1 simply because I thought it was fine, e.g., swap
entry won't be kept in shmem ptes so skipped is okay (it is never okay with
shmem uffd-wp but uffd-wp code is not landed yet).  However I just remembered
there could also be e.g. shmem migration entries if I'm not wrong.  From that
pov, skipping swap entries for unmap_mapping_page() seems wrong.  Would you
please help check?

It'll be great if you can comment on patch 1 too, to see whether that's okay
and what I could have been missing there (e.g., if you have other concern on
breaking stuff, I'll be happy to test).

v2:
- Patch "mm: Clear vmf->pte after pte_unmap_same() returns"
  - Remove one comment [David]
- Collect r-b for patch 2/3
- Rewrite the last two patches to drop ZAP_FLAG_CHECK_MAPPING, dropping
  Alistair's r-b on patch 5 because it changed [David, Matthew]

===== v1 cover letter =====

I picked up these patches from uffd-wp v5 series here:

https://lore.kernel.org/lkml/20210715201422.211004-1-peterx@redhat.com/

IMHO all of them are very nice cleanups to existing code already, they're all
small and self-contained.  They'll be needed by uffd-wp coming series.  I would
appreciate if they can be accepted earlier, so as to not carry them over always
with the uffd-wp series.

I removed some CC from the uffd-wp v5 series to reduce the noise, and added a
few more into it.

Reviews are greatly welcomed, thanks.

Peter Xu (5):
  mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte
  mm: Clear vmf->pte after pte_unmap_same() returns
  mm: Drop first_index/last_index in zap_details
  mm: Add zap_skip_check_mapping() helper
  mm: Add ZAP_FLAG_SKIP_SWAP and zap_flags

 include/linux/mm.h | 33 ++++++++++++++++++--
 mm/memory.c        | 76 +++++++++++++++++++---------------------------
 mm/shmem.c         |  1 -
 mm/userfaultfd.c   |  3 +-
 4 files changed, 62 insertions(+), 51 deletions(-)

-- 
2.31.1