linux-kernel - Re: [PATCH v2 15/18] perf: arm_spe: Handle guest/host exclusion flags

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Message-ID: <20191220180959.GF25258@lakrids.cambridge.arm.com>
Date:   Fri, 20 Dec 2019 18:10:00 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Andrew Murray <andrew.murray@....com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 15/18] perf: arm_spe: Handle guest/host exclusion flags

On Fri, Dec 20, 2019 at 02:30:22PM +0000, Andrew Murray wrote:
> A side effect of supporting the SPE in guests is that we prevent the
> host from collecting data whilst inside a guest thus creating a black-out
> window. This occurs because instead of emulating the SPE, we share it
> with our guests.

We used to permit this; do we know if anyone is using it?

Thanks,
Mark.

> Let's accurately describe our capabilities by using the perf exclude
> flags to prevent !exclude_guest and exclude_host flags from being used.
> 
> Signed-off-by: Andrew Murray <andrew.murray@....com>
> ---
>  drivers/perf/arm_spe_pmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
> index 2d24af4cfcab..3703dbf459de 100644
> --- a/drivers/perf/arm_spe_pmu.c
> +++ b/drivers/perf/arm_spe_pmu.c
> @@ -679,6 +679,9 @@ static int arm_spe_pmu_event_init(struct perf_event *event)
>  	if (attr->exclude_idle)
>  		return -EOPNOTSUPP;
>  
> +	if (!attr->exclude_guest || attr->exclude_host)
> +		return -EOPNOTSUPP;
> +
>  	/*
>  	 * Feedback-directed frequency throttling doesn't work when we
>  	 * have a buffer of samples. We'd need to manually count the
> -- 
> 2.21.0
>