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    SubjectRe: [PATCH] Revert "perf machine: Fix paranoid check in machine__set_kernel_mmap()"
    On Wed, Apr 11, 2018 at 07:29:40PM -0500, Kim Phillips wrote:
    > On Thu, 12 Apr 2018 08:31:09 +0900
    > Namhyung Kim <namhyung@kernel.org> wrote:
    >
    > > Hello,
    >
    > Hi,
    >
    > > On Wed, Apr 11, 2018 at 06:07:52PM -0500, Kim Phillips wrote:
    > > > ---
    > > > It's not clear to me what the specific intent of the original commit
    > > > was, thus the revert.
    > >
    > > Hmm.. maybe your kernel map has non-zero start and zero end. I
    >
    > On x86, the first line in /proc/kallsyms is:
    >
    > 0000000000000000 A irq_stack_union
    >
    > On arm64, it's:
    >
    > ffff200008080000 t _head
    >
    > Another arm64 box has:
    >
    > ffff000008080000 t _head
    >
    > (neither have RANDOMIZE_BASE set FWIW)
    >
    > > thought it was just from an old or invalid data. But now I think that
    >
    > It would be good to know what that was, yes.
    >
    > > overflow can create it.. could you please show me the mmap event?
    > >
    > > $ perf script --show-mmap-events
    >
    > Here you go:
    >
    > swapper 0 [000] 0.000000: PERF_RECORD_MMAP -1/0: [0xffff200008080000(0xdffff7f7ffff) @ 0xffff200008080000]: x [kernel.kallsyms]_text

    0xffff200008080000
    + 0xdffff7f7ffff
    --------------------
    0xffffffffffffffff

    So it should have ~0ULL of the 'end' already. I don't know why it
    caused the problem.. Was it from the `perf.good`?


    > swapper 0 [000] 0.000000: PERF_RECORD_MMAP -1/0: [0xffff2000021e0000(0x18000) @ 0]: x /lib/modules/4.16.0+/kernel/drivers/bus/arm-ccn.ko

    Hmm.. also it seems arm64 loads modules under the kernel. Then the
    fixup logic in machine__create_kernel_maps() won't work. Also as we
    don't use the map_groups__fixup_end() anymore I think it's ok just
    checking the end address.

    Thanks,
    Namhyung

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