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    Subject[ 029/104] s390/memory hotplug: prevent offline of active memory increments
    Date
    3.8-stable review patch.  If anyone has any objections, please let me know.

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

    From: Heiko Carstens <heiko.carstens@de.ibm.com>

    commit 94c163663fc1dcfc067a5fb3cc1446b9469975ce upstream.

    In case a machine supports memory hotplug all active memory increments
    present at IPL time have been initialized with a "usecount" of 1.
    This is wrong if the memory increment size is larger than the memory
    section size of the memory hotplug code. If that is the case the
    usecount must be initialized with the number of memory sections that
    fit into one memory increment.
    Otherwise it is possible to put a memory increment into standby state
    even if there are still active sections.
    Afterwards addressing exceptions might happen which cause the kernel
    to panic.
    However even worse, if a memory increment was put into standby state
    and afterwards into active state again, it's contents would have been
    zeroed, leading to memory corruption.

    This was only an issue for machines that support standby memory and
    have at least 256GB memory.

    This is broken since commit fdb1bb15 "[S390] sclp/memory hotplug: fix
    initial usecount of increments".

    Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
    Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/s390/char/sclp_cmd.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/drivers/s390/char/sclp_cmd.c
    +++ b/drivers/s390/char/sclp_cmd.c
    @@ -567,6 +567,8 @@ static void __init sclp_add_standby_memo
    add_memory_merged(0);
    }

    +#define MEM_SCT_SIZE (1UL << SECTION_SIZE_BITS)
    +
    static void __init insert_increment(u16 rn, int standby, int assigned)
    {
    struct memory_increment *incr, *new_incr;
    @@ -579,7 +581,7 @@ static void __init insert_increment(u16
    new_incr->rn = rn;
    new_incr->standby = standby;
    if (!standby)
    - new_incr->usecount = 1;
    + new_incr->usecount = rzm > MEM_SCT_SIZE ? rzm/MEM_SCT_SIZE : 1;
    last_rn = 0;
    prev = &sclp_mem_list;
    list_for_each_entry(incr, &sclp_mem_list, list) {



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