Re: [Devel] [PATCH hci-8.1 5/8] oracle/mm: set MMF_HAS_PINNED on the mm receiving preserved pages

[no-reply@sashiko.virtuozzo.com]

> fork decides whether an anonymous page may be pinned with
> folio_needs_cow_for_dma(), which looks at MMF_HAS_PINNED of the parent
> mm before folio_maybe_dma_pinned(). Only GUP sets that flag, in the mm
> whose pages it pins. Pages preserved across exec keep a long-term pin
> taken through the old mm, but the new mm never has the flag, so a fork
> in the new image clears PageAnonExclusive of a pinned page and maps it
> read-only in both processes. The next write in the parent copies the
> page and the device keeps the old one. A debug kernel catches the
> shared page when the pin is dropped:
> 
>   page dumped because: VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page))
>   kernel BUG at mm/gup.c:66!
>   RIP: 0010:sanity_check_pinned_pages+0x237/0x960
>    unpin_user_pages
>    gup_test_release
>    __fput
> 
> Set MMF_HAS_PINNED on the new mm when the old one has it.
> 
> Fixes: 37d9f55655ea ("oracle/mm: do not write protect COW mappings when preserving across exec")
> https://virtuozzo.atlassian.net/browse/VSTOR-150231
> 
> Feature: oracle/mm: MADV_DOEXEC madvise() flag
> Assisted-by: LLM
> Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261014-b4-prep-khorenko-vstor-149847-2-doexec-pinned-memory-v1-0-36f1120f9b57@virtuozzo.com?part=5


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