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    SubjectRe: [PATCH 3/5] mm/migrate.c: fix potential indeterminate pte entry in migrate_vma_insert_page()
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    On 2021/3/23 19:07, Alistair Popple wrote:
    > On Tuesday, 23 March 2021 9:26:43 PM AEDT David Hildenbrand wrote:
    >> On 20.03.21 10:36, Miaohe Lin wrote:
    >>> If the zone device page does not belong to un-addressable device memory,
    >>> the variable entry will be uninitialized and lead to indeterminate pte
    >>> entry ultimately. Fix this unexpectant case and warn about it.
    >>
    >> s/unexpectant/unexpected/
    >>
    >>>
    >>> Fixes: df6ad69838fc ("mm/device-public-memory: device memory cache
    > coherent with CPU")
    >>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
    >>> ---
    >>> mm/migrate.c | 7 +++++++
    >>> 1 file changed, 7 insertions(+)
    >>>
    >>> diff --git a/mm/migrate.c b/mm/migrate.c
    >>> index 20a3bf75270a..271081b014cb 100644
    >>> --- a/mm/migrate.c
    >>> +++ b/mm/migrate.c
    >>> @@ -2972,6 +2972,13 @@ static void migrate_vma_insert_page(struct
    > migrate_vma *migrate,
    >>>
    >>> swp_entry = make_device_private_entry(page, vma->vm_flags &
    > VM_WRITE);
    >>> entry = swp_entry_to_pte(swp_entry);
    >>> + } else {
    >>> + /*
    >>> + * For now we only support migrating to un-addressable
    >>> + * device memory.
    >>> + */
    >>> + WARN_ON(1);
    >>> + goto abort;
    >>
    >> Fix it by crashing the kernel with panic_on_warn? :)
    >>
    >> If this case can actual happen, than no WARN_ON() - rather a
    >> pr_warn_once(). If this case cannot happen, why do we even care (it's
    >> not a fix then)?
    >
    > There is also already a check for this case in migrate_vma_pages(). The
    > problem is it happens after the call to migrate_vma_insert_page(). I wonder if
    > instead it would be better just to move the existing check to before that
    > call?
    >

    Yes, sounds good! Many thanks for your advice! :)

    > >
    > .
    >

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