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    SubjectRe: [PATCH 1/2] tomoyo: Convert get_user_pages*() to pin_user_pages*()
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    On 11/7/20 12:24 AM, Souptick Joarder wrote:
    > In 2019, we introduced pin_user_pages*() and now we are converting
    > get_user_pages*() to the new API as appropriate. [1] & [2] could
    > be referred for more information. This is case 5 as per document [1].

    It turns out that Case 5 can be implemented via a better pattern, as long
    as we're just dealing with a page at a time, briefly:

    lock_page()
    write to page's data
    unlock_page()

    ...which neatly synchronizes with writeback and other fs activities.

    I was going to track down the Case 5's and do that [1].

    +CC Jan and Matthew, to keep us on the straight and narrow, just in case
    I'm misunderstanding something.

    [1] https://lore.kernel.org/r/e78fb7af-627b-ce80-275e-51f97f1f3168@nvidia.com

    thanks,
    --
    John Hubbard
    NVIDIA

    >
    > [1] Documentation/core-api/pin_user_pages.rst
    >
    > [2] "Explicit pinning of user-space pages":
    > https://lwn.net/Articles/807108/
    >
    > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
    > Cc: John Hubbard <jhubbard@nvidia.com>
    > ---
    > security/tomoyo/domain.c | 4 ++--
    > 1 file changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
    > index dc4ecc0..bd748be 100644
    > --- a/security/tomoyo/domain.c
    > +++ b/security/tomoyo/domain.c
    > @@ -914,7 +914,7 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
    > * (represented by bprm). 'current' is the process doing
    > * the execve().
    > */
    > - if (get_user_pages_remote(bprm->mm, pos, 1,
    > + if (pin_user_pages_remote(bprm->mm, pos, 1,
    > FOLL_FORCE, &page, NULL, NULL) <= 0)
    > return false;
    > #else
    > @@ -936,7 +936,7 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
    > }
    > /* Same with put_arg_page(page) in fs/exec.c */
    > #ifdef CONFIG_MMU
    > - put_page(page);
    > + unpin_user_page(page);
    > #endif
    > return true;
    > }
    >

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