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    SubjectRe: [patch 0/4] x86/perf/intel/cstate: Fix cpu hotplug handling and make it modular
    On Sun, Mar 20, 2016 at 06:59:01PM -0000, Thomas Gleixner wrote:
    > The perf cstate driver is yet another trainwreck vs. cpu hotplug handling. The
    > hotplug code is not only disfunctional, it's also a uncomprehensible mess.
    >
    > The following series fixes the hotplug functionality, sanitizes error handling
    > and makes the driver modular.
    >

    I needed the below to not make it insta explode with perf_fuzzer.

    At cstate_pmu_event_init() event->cpu can still be -1, that results in
    funny masks being dereferenced.

    With the probe thing, we need to clear msr[].attr for all those that are
    not available, other event_init() will happily still select them
    (they're just not visible in sysfs, and guess how much the fuzzer cares
    about that.. :-).


    --- a/arch/x86/events/intel/cstate.c
    +++ b/arch/x86/events/intel/cstate.c
    @@ -267,7 +267,7 @@ static ssize_t cstate_get_attr_cpumask(s
    static int cstate_pmu_event_init(struct perf_event *event)
    {
    u64 cfg = event->attr.config;
    - unsigned int cpu;
    + int cpu;

    if (event->attr.type != event->pmu->type)
    return -ENOENT;
    @@ -282,6 +282,9 @@ static int cstate_pmu_event_init(struct
    event->attr.sample_period) /* no sampling */
    return -EINVAL;

    + if (event->cpu < 0)
    + return -EINVAL;
    +
    if (event->pmu == &cstate_core_pmu) {
    if (cfg >= PERF_CSTATE_CORE_EVENT_MAX)
    return -EINVAL;
    @@ -547,22 +550,24 @@ MODULE_DEVICE_TABLE(x86cpu, intel_cstate
    * Probe the cstate events and insert the available one into sysfs attrs
    * Return false if there are no available events.
    */
    -static bool __init cstate_probe_msr(const unsigned long evmsk,
    - struct perf_cstate_msr *msr,
    - struct attribute **attrs)
    +static bool __init cstate_probe_msr(const unsigned long evmsk, int max,
    + struct perf_cstate_msr *msr,
    + struct attribute **attrs)
    {
    bool found = false;
    unsigned int bit;
    u64 val;

    - for_each_set_bit(bit, &evmsk, sizeof(evmsk) * BITS_PER_BYTE) {
    - /* Verify whether the MSR is accessible */
    - if (!rdmsrl_safe(msr[bit].msr, &val)) {
    + for (bit = 0; bit < max; bit++) {
    + if (test_bit(bit, &evmsk) && !rdmsrl_safe(msr[bit].msr, &val)) {
    *attrs++ = &msr[bit].attr->attr.attr;
    found = true;
    + } else {
    + msr[bit].attr = NULL;
    }
    }
    *attrs = NULL;
    +
    return found;
    }

    @@ -572,11 +577,13 @@ static int __init cstate_probe(const str
    if (cm->quirks & SLM_PKG_C6_USE_C7_MSR)
    pkg_msr[PERF_CSTATE_PKG_C6_RES].msr = MSR_PKG_C7_RESIDENCY;

    - has_cstate_core = cstate_probe_msr(cm->core_events, core_msr,
    - core_events_attrs);
    -
    - has_cstate_pkg = cstate_probe_msr(cm->pkg_events, pkg_msr,
    - pkg_events_attrs);
    + has_cstate_core = cstate_probe_msr(cm->core_events,
    + PERF_CSTATE_CORE_EVENT_MAX,
    + core_msr, core_events_attrs);
    +
    + has_cstate_pkg = cstate_probe_msr(cm->pkg_events,
    + PERF_CSTATE_PKG_EVENT_MAX,
    + pkg_msr, pkg_events_attrs);

    return (has_cstate_core || has_cstate_pkg) ? 0 : -ENODEV;
    }
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