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    Subject[PATCH 10/19] x86, mpx: Trace the attempts to find bounds tables
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    From: Dave Hansen <dave.hansen@linux.intel.com>

    There are two different events being traced here. They are
    doing similar things so share a trace "EVENT_CLASS" and are
    presented together.

    1. Trace when MPX is zapping pages "mpx_unmap_zap":

    When MPX can not free an entire bounds table, it will
    instead try to zap unused parts of a bounds table to free
    the backing memory. This decreases RSS (resident set
    size) without decreasing the virtual space allocated
    for bounds tables.

    2. Trace attempts to find bounds tables "mpx_unmap_search":

    This event traces any time we go looking to unmap a
    bounds table for a given virtual address range. This is
    useful to ensure that the kernel actually "tried" to free
    a bounds table versus times it succeeded in finding one.

    It might try and fail if it realized that a table was
    shared with an adjacent VMA which is not being unmapped.

    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    ---

    b/arch/x86/include/asm/trace/mpx.h | 32 ++++++++++++++++++++++++++++++++
    b/arch/x86/mm/mpx.c | 2 ++
    2 files changed, 34 insertions(+)

    diff -puN arch/x86/include/asm/trace/mpx.h~mpx-trace_unmap_zap arch/x86/include/asm/trace/mpx.h
    --- a/arch/x86/include/asm/trace/mpx.h~mpx-trace_unmap_zap 2015-06-01 10:24:06.928852740 -0700
    +++ b/arch/x86/include/asm/trace/mpx.h 2015-06-01 10:24:06.934853011 -0700
    @@ -63,6 +63,38 @@ TRACE_EVENT(bounds_exception_mpx,
    __entry->bndstatus)
    );

    +DECLARE_EVENT_CLASS(mpx_range_trace,
    +
    + TP_PROTO(unsigned long start,
    + unsigned long end),
    + TP_ARGS(start, end),
    +
    + TP_STRUCT__entry(
    + __field(unsigned long, start)
    + __field(unsigned long, end)
    + ),
    +
    + TP_fast_assign(
    + __entry->start = start;
    + __entry->end = end;
    + ),
    +
    + TP_printk("[0x%p:0x%p]",
    + (void *)__entry->start,
    + (void *)__entry->end
    + )
    +);
    +
    +DEFINE_EVENT(mpx_range_trace, mpx_unmap_zap,
    + TP_PROTO(unsigned long start, unsigned long end),
    + TP_ARGS(start, end)
    +);
    +
    +DEFINE_EVENT(mpx_range_trace, mpx_unmap_search,
    + TP_PROTO(unsigned long start, unsigned long end),
    + TP_ARGS(start, end)
    +);
    +
    #else

    /*
    diff -puN arch/x86/mm/mpx.c~mpx-trace_unmap_zap arch/x86/mm/mpx.c
    --- a/arch/x86/mm/mpx.c~mpx-trace_unmap_zap 2015-06-01 10:24:06.930852830 -0700
    +++ b/arch/x86/mm/mpx.c 2015-06-01 10:24:06.934853011 -0700
    @@ -668,6 +668,7 @@ static int zap_bt_entries(struct mm_stru

    len = min(vma->vm_end, end) - addr;
    zap_page_range(vma, addr, len, NULL);
    + trace_mpx_unmap_zap(addr, addr+len);

    vma = vma->vm_next;
    addr = vma->vm_start;
    @@ -840,6 +841,7 @@ static int mpx_unmap_tables(struct mm_st
    long __user *bd_entry, *bde_start, *bde_end;
    unsigned long bt_addr;

    + trace_mpx_unmap_search(start, end);
    /*
    * "Edge" bounds tables are those which are being used by the region
    * (start -> end), but that may be shared with adjacent areas. If they
    _

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