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    Subject[PATCH v4 2/5] mm/gup: follow_pfn_pte(): -EEXIST cleanup
    Date
    Remove a quirky special case from follow_pfn_pte(), and adjust its
    callers to match. Caller changes include:

    __get_user_pages(): Regardless of any FOLL_* flags, get_user_pages() and
    its variants should handle PFN-only entries by stopping early, if the
    caller expected **pages to be filled in. This makes for a more reliable
    API, as compared to the previous approach of skipping over such entries
    (and thus leaving them silently unwritten).

    move_pages(): squash the -EEXIST error return from follow_page() into
    -EFAULT, because -EFAULT is listed in the man page, whereas -EEXIST is
    not.

    Cc: Peter Xu <peterx@redhat.com>
    Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
    Signed-off-by: John Hubbard <jhubbard@nvidia.com>
    ---
    mm/gup.c | 13 ++++++++-----
    mm/migrate.c | 7 +++++++
    2 files changed, 15 insertions(+), 5 deletions(-)

    diff --git a/mm/gup.c b/mm/gup.c
    index 80229ecf0114..2df0d0103c43 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -464,10 +464,6 @@ static struct page *no_page_table(struct vm_area_struct *vma,
    static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
    pte_t *pte, unsigned int flags)
    {
    - /* No page to get reference */
    - if (flags & (FOLL_GET | FOLL_PIN))
    - return -EFAULT;
    -
    if (flags & FOLL_TOUCH) {
    pte_t entry = *pte;

    @@ -1205,8 +1201,15 @@ static long __get_user_pages(struct mm_struct *mm,
    } else if (PTR_ERR(page) == -EEXIST) {
    /*
    * Proper page table entry exists, but no corresponding
    - * struct page.
    + * struct page. If the caller expects **pages to be
    + * filled in, bail out now, because that can't be done
    + * for this page.
    */
    + if (pages) {
    + ret = PTR_ERR(page);
    + goto out;
    + }
    +
    goto next_page;
    } else if (IS_ERR(page)) {
    ret = PTR_ERR(page);
    diff --git a/mm/migrate.c b/mm/migrate.c
    index c7da064b4781..be0d5ae36dc1 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -1761,6 +1761,13 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
    continue;
    }

    + /*
    + * The move_pages() man page does not have an -EEXIST choice, so
    + * use -EFAULT instead.
    + */
    + if (err == -EEXIST)
    + err = -EFAULT;
    +
    /*
    * If the page is already on the target node (!err), store the
    * node, otherwise, store the err.
    --
    2.35.1
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