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    Subject[PATCH 4.4 07/37] kaiser: KAISER depends on SMP
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Hugh Dickins <hughd@google.com>


    It is absurd that KAISER should depend on SMP, but apparently nobody
    has tried a UP build before: which breaks on implicit declaration of
    function 'per_cpu_offset' in arch/x86/mm/kaiser.c.

    Now, you would expect that to be trivially fixed up; but looking at
    the System.map when that block is #ifdef'ed out of kaiser_init(),
    I see that in a UP build __per_cpu_user_mapped_end is precisely at
    __per_cpu_user_mapped_start, and the items carefully gathered into
    that section for user-mapping on SMP, dispersed elsewhere on UP.

    So, some other kind of section assignment will be needed on UP,
    but implementing that is not a priority: just make KAISER depend
    on SMP for now.

    Also inserted a blank line before the option, tidied up the
    brief Kconfig help message, and added an "If unsure, Y".

    Signed-off-by: Hugh Dickins <hughd@google.com>
    Acked-by: Jiri Kosina <jkosina@suse.cz>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    security/Kconfig | 10 ++++++----
    1 file changed, 6 insertions(+), 4 deletions(-)

    --- a/security/Kconfig
    +++ b/security/Kconfig
    @@ -30,14 +30,16 @@ config SECURITY
    model will be used.

    If you are unsure how to answer this question, answer N.
    +
    config KAISER
    bool "Remove the kernel mapping in user mode"
    default y
    - depends on X86_64
    - depends on !PARAVIRT
    + depends on X86_64 && SMP && !PARAVIRT
    help
    - This enforces a strict kernel and user space isolation in order to close
    - hardware side channels on kernel address information.
    + This enforces a strict kernel and user space isolation, in order
    + to close hardware side channels on kernel address information.
    +
    + If you are unsure how to answer this question, answer Y.

    config KAISER_REAL_SWITCH
    bool "KAISER: actually switch page tables"

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