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    SubjectRe: [PATCH 07/11] unpaged: COW on VM_UNPAGED
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    From: Hugh Dickins <hugh@veritas.com>
    Date: Thu, 17 Nov 2005 19:37:23 +0000 (GMT)

    > Remove the BUG_ON(vma->vm_flags & VM_UNPAGED) from do_wp_page, and let
    > it do Copy-On-Write without touching the VM_UNPAGED's page counts - but
    > this is incomplete, because the anonymous page it inserts will itself
    > need to be handled, here and in other functions - next patch.
    >
    > We still don't copy the page if the pfn is invalid, because the
    > copy_user_highpage interface does not allow it. But that's not been
    > a problem in the past: can be added in later if the need arises.
    >
    > Signed-off-by: Hugh Dickins <hugh@veritas.com>

    Do we even need this? It is a very serious question...

    The cases I've seen, and am aware of, I documented in a previous
    mail and those involve MAP_PRIVATE maps of /dev/mem or other
    similar fixed page mapping devices.

    Which case truly needs COW faults on VM_RESERVED memory which
    isn't an application bug of some sort?
    -
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