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    Subject[PATCH 4.14 432/496] perf/x86/intel: Fix large period handling on Broadwell CPUs
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Kan Liang <kan.liang@linux.intel.com>

    [ Upstream commit f605cfca8c39ffa2b98c06d2b9f30ba64f1e54e3 ]

    Large fixed period values could be truncated on Broadwell, for example:

    perf record -e cycles -c 10000000000

    Here the fixed period is 0x2540BE400, but the period which finally applied is
    0x540BE400 - which is wrong.

    The reason is that x86_pmu::limit_period() uses an u32 parameter, so the
    high 32 bits of 'period' get truncated.

    This bug was introduced in:

    commit 294fe0f52a44 ("perf/x86/intel: Add INST_RETIRED.ALL workarounds")

    It's safe to use u64 instead of u32:

    - Although the 'left' is s64, the value of 'left' must be positive when
    calling limit_period().

    - bdw_limit_period() only modifies the lowest 6 bits, it doesn't touch
    the higher 32 bits.

    Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Fixes: 294fe0f52a44 ("perf/x86/intel: Add INST_RETIRED.ALL workarounds")
    Link: http://lkml.kernel.org/r/1519926894-3520-1-git-send-email-kan.liang@linux.intel.com
    [ Rewrote unacceptably bad changelog. ]
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/events/intel/core.c | 2 +-
    arch/x86/events/perf_event.h | 2 +-
    2 files changed, 2 insertions(+), 2 deletions(-)

    --- a/arch/x86/events/intel/core.c
    +++ b/arch/x86/events/intel/core.c
    @@ -3196,7 +3196,7 @@ glp_get_event_constraints(struct cpu_hw_
    * Therefore the effective (average) period matches the requested period,
    * despite coarser hardware granularity.
    */
    -static unsigned bdw_limit_period(struct perf_event *event, unsigned left)
    +static u64 bdw_limit_period(struct perf_event *event, u64 left)
    {
    if ((event->hw.config & INTEL_ARCH_EVENT_MASK) ==
    X86_CONFIG(.event=0xc0, .umask=0x01)) {
    --- a/arch/x86/events/perf_event.h
    +++ b/arch/x86/events/perf_event.h
    @@ -556,7 +556,7 @@ struct x86_pmu {
    struct x86_pmu_quirk *quirks;
    int perfctr_second_write;
    bool late_ack;
    - unsigned (*limit_period)(struct perf_event *event, unsigned l);
    + u64 (*limit_period)(struct perf_event *event, u64 l);

    /*
    * sysfs attrs

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