Hi German,

On Thu, Feb 10, 2022 at 05:23:50PM +0000, German Gomez wrote:

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One way to fix this is by caching the value of the CX bit during the
initialization of the PMU event, so that it remains consistent for the
duration of the session.

[...]

So the patch makes sense to me.  Just a minor comment:

Here we can define a u64 for recording pmscr value rather than a
bool value.

struct arm_spe_pmu {
    ...
    u64 pmscr;
};

I agree with the comment from Will that it makes more sense to store the
value of the register in the perf_event somehow (due to misunderstanding
from my side, I thought arm_spe_pmu struct was local to the session).

It's shame that I miss this point :) As you said, struct arm_spe_pmu is
a data structure for Arm SPE device driver instance and it's not
allocated for perf session.

What about perf_event's void *pmu_private?

Before we use perf_event::pmu_private, could you check the data
structure arm_spe_pmu_buf firstly?  This data structure is allocated
when setup AUX ring buffer (so it's allocated for perf session).
IIUC, the function arm_spe_pmu_setup_aux() will be invoked in the perf
process, so it's good for us to initialize pmscr in this function.

Thanks,
Leo

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