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    SubjectRe: Question about PRIVATE_FUTEX
    Minchan Kim a écrit :
    > Hi, Peter and Eric.
    >
    > I am not expert about futex.
    > I am sorry if this is dumb question.
    >
    > If we use private futex, get_futex_key don't call get_user_pages_fast
    > which pins page at page table.
    > Then, get_futex_value_locked calls __cpy_from_user_inatomic with
    > pagefault_disable.
    >
    > Who make sure the user page is mapped at app's page table ?
    >

    Nothing makes sure user page is mapped, as we dont have to (for private futexes
    at least, since the 'key' is a combination of the futex virtual address (not
    depending on the underlying physical page) and the task mm (sort of a static
    offset per task)

    If no page is mapped, a normal error should be returned to user, since
    access to futex location will trigger a fault.


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