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

[John Garry]

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@ubuntu:~$ 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