• Michael S. Tsirkin's avatar
    [PATCH] madvise MADV_DONTFORK/MADV_DOFORK · f8225661
    Michael S. Tsirkin authored
    Currently, copy-on-write may change the physical address of a page even if the
    user requested that the page is pinned in memory (either by mlock or by
    get_user_pages).  This happens if the process forks meanwhile, and the parent
    writes to that page.  As a result, the page is orphaned: in case of
    get_user_pages, the application will never see any data hardware DMA's into
    this page after the COW.  In case of mlock'd memory, the parent is not getting
    the realtime/security benefits of mlock.
    
    In particular, this affects the Infiniband modules which do DMA from and into
    user pages all the time.
    
    This patch adds madvise options to control whether memory range is inherited
    across fork.  Useful e.g.  for when hardware is doing DMA from/into these
    pages.  Could also be useful to an application wanting to speed up its forks
    by cutting large areas out of consideration.
    Signed-off-by: default avatarMichael S. Tsirkin <mst@mellanox.co.il>
    Acked-by: default avatarHugh Dickins <hugh@veritas.com>
    Cc: Michael Kerrisk <mtk-manpages@gmx.net>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    f8225661
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