linux-kernel - Re: [RFC PATCH] perf/smmuv3: Fix shared interrupt handling

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Message-ID: <34dd7c2e-b6db-684f-f0a2-73f2e6951308@huawei.com>
Date:   Thu, 9 Apr 2020 08:02:20 +0100
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>,
        "will@...nel.org" <will@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>,
        "harb@...erecomputing.com" <harb@...erecomputing.com>,
        "tuanphan@...amperecomputing.com" <tuanphan@...amperecomputing.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] perf/smmuv3: Fix shared interrupt handling

On 08/04/2020 17:49, Robin Murphy wrote:
> IRQF_SHARED is dangerous, since it allows other agents to retarget the
> IRQ's affinity without migrating PMU contexts to match, breaking the way
> in which perf manages mutual exclusion for accessing events. Although
> this means it's not realistically possible to support PMU IRQs being
> shared with other drivers, we *can* handle sharing between multiple PMU
> instances with some explicit affinity bookkeeping and manual interrupt
> multiplexing.

Hi Robin,

Out of curiosity, do we even need to support shared interrupts for any 
implementations today?

D06 board:

john@...ntu:~$ more /proc/interrupts | grep smmuv3-pmu

  989:  0  0  0  0  ITS-pMSI 133120 Edge  smmuv3-pmu
  990:  0  0  0  0  ITS-pMSI 135168 Edge  smmuv3-pmu
  991:  0  0  0  0  ITS-pMSI 137216 Edge  smmuv3-pmu
  992:  0  0  0  0  ITS-pMSI 139264 Edge  smmuv3-pmu
  993:  0  0  0  0  ITS-pMSI 141312 Edge  smmuv3-pmu
  994:  0  0  0  0  ITS-pMSI 143360 Edge  smmuv3-pmu
  995:  0  0  0  0  ITS-pMSI 145408 Edge  smmuv3-pmu
  996:  0  0  0  0  ITS-pMSI 147456 Edge  smmuv3-pmu

Thanks,
John