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Re: [PATCH 21/21] x86/intel_rdt/mbm: Handle counter overflow

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On Mon, 26 Jun 2017, Vikas Shivappa wrote:
> +static void mbm_update(struct rdt_domain *d, int rmid)
> +{
> +	struct rmid_read rr;
> +
> +	rr.first = false;
> +	rr.d = d;
> +
> +	if (is_mbm_total_enabled()) {
> +		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
> +		__mon_event_count(rmid, &rr);

This is broken as it is not protected against a concurrent read from user
space which comes in via a smp function call.

This means both the internal state and __rmid_read() are unprotected.

I'm not sure whether it's enough to disable interrupts around
__mon_event_count(), but that's the minimal protection required. It's
definitely good enough for __rmid_read(), but it might not be sufficient
for protecting domain->mbm_[local|total]. I leave the exercise of figuring
that out to you.

Thanks,

	tglx

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[PATCH V1 00/21] x86/cqm3: Resctrl based cqm Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
  [PATCH 16/21] x86/intel_rdt/cqm: Add mount,umount support Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 16/21] x86/intel_rdt/cqm: Add mount,umount support Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 15:30 +0200
  [PATCH 20/21] x86/intel_rdt/mbm: Add mbm counter initialization Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
  [PATCH 13/21] x86/intel_rdt/cqm: Add cpus file support Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 13/21] x86/intel_rdt/cqm: Add cpus file support Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 13:20 +0200
    Re: [PATCH 13/21] x86/intel_rdt/cqm: Add cpus file support Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 14:40 +0200
  [PATCH 15/21] x86/intel_rdt/cqm: Add rmdir support Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 15/21] x86/intel_rdt/cqm: Add rmdir support Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 15:20 +0200
  [PATCH 03/21] x86/intel_rdt/cqm: Documentation for resctrl based RDT Monitoring Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
  [PATCH 21/21] x86/intel_rdt/mbm: Handle counter overflow Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 21/21] x86/intel_rdt/mbm: Handle counter overflow Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 16:00 +0200
  [PATCH 14/21] x86/intel_rdt/cqm: Add mon_data Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 14/21] x86/intel_rdt/cqm: Add mon_data Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 14:50 +0200
  [PATCH 17/21] x86/intel_rdt/cqm: Add sched_in support Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 17/21] x86/intel_rdt/cqm: Add sched_in support Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 15:40 +0200
  [PATCH 12/21] x86/intel_rdt/cqm: Add tasks file support Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 12/21] x86/intel_rdt/cqm: Add tasks file support Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 13:10 +0200
  [PATCH 08/21] x86/intel_rdt/cqm: Add RMID(Resource monitoring ID) management Vikas Shivappa <vikas.shivappa@linux.intel.com> - 2017-06-26 21:00 +0200
    Re: [PATCH 08/21] x86/intel_rdt/cqm: Add RMID(Resource monitoring  ID) management Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 12:10 +0200
      Re: [PATCH 08/21] x86/intel_rdt/cqm: Add RMID(Resource monitoring  ID) management Thomas Gleixner <tglx@linutronix.de> - 2017-07-03 12:00 +0200

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