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Subject: Re: [PATCH v4 4/9] drm/i915/perf: open access for CAP_SYS_PERFMON
 privileged process
To:     Alexey Budankov <alexey.budankov@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        "jani.nikula@linux.intel.com" <jani.nikula@linux.intel.com>,
        "joonas.lahtinen@linux.intel.com" <joonas.lahtinen@linux.intel.com>,
        "rodrigo.vivi@intel.com" <rodrigo.vivi@intel.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "james.bottomley@hansenpartnership.com" 
        <james.bottomley@hansenpartnership.com>,
        Serge Hallyn <serge@hallyn.com>,
        James Morris <jmorris@namei.org>,
        Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Robert Richter <rric@kernel.org>
Cc:     Jiri Olsa <jolsa@redhat.com>, Andi Kleen <ak@linux.intel.com>,
        Stephane Eranian <eranian@google.com>,
        Igor Lubashev <ilubashe@akamai.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        Song Liu <songliubraving@fb.com>,
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References: <c0460c78-b1a6-b5f7-7119-d97e5998f308@linux.intel.com>
 <ea050255-a125-8831-ce91-ee23bd6ad08b@linux.intel.com>
From:   Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Organization: Intel Corporation (UK) Ltd. - Co. Reg. #1134945 - Pipers Way,
 Swindon SN3 1RJ
Message-ID: <d5f908f3-b545-7953-8c72-ceb7177609d3@intel.com>
Date:   Thu, 19 Dec 2019 11:10:29 +0200
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On 18/12/2019 11:27, Alexey Budankov wrote:
> Open access to i915_perf monitoring for CAP_SYS_PERFMON privileged
> processes. For backward compatibility reasons access to i915_perf
> subsystem remains open for CAP_SYS_ADMIN privileged processes but
> CAP_SYS_ADMIN usage for secure i915_perf monitoring is discouraged
> with respect to CAP_SYS_PERFMON capability.
>
> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>

Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

> ---
>   drivers/gpu/drm/i915/i915_perf.c | 13 ++++++-------
>   1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index e42b86827d6b..e2697f8d04de 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -2748,10 +2748,10 @@ i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
>   	/* Similar to perf's kernel.perf_paranoid_cpu sysctl option
>   	 * we check a dev.i915.perf_stream_paranoid sysctl option
>   	 * to determine if it's ok to access system wide OA counters
> -	 * without CAP_SYS_ADMIN privileges.
> +	 * without CAP_SYS_PERFMON or CAP_SYS_ADMIN privileges.
>   	 */
>   	if (privileged_op &&
> -	    i915_perf_stream_paranoid && !capable(CAP_SYS_ADMIN)) {
> +	    i915_perf_stream_paranoid && !perfmon_capable()) {
>   		DRM_DEBUG("Insufficient privileges to open system-wide i915 perf stream\n");
>   		ret = -EACCES;
>   		goto err_ctx;
> @@ -2939,9 +2939,8 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
>   			} else
>   				oa_freq_hz = 0;
>   
> -			if (oa_freq_hz > i915_oa_max_sample_rate &&
> -			    !capable(CAP_SYS_ADMIN)) {
> -				DRM_DEBUG("OA exponent would exceed the max sampling frequency (sysctl dev.i915.oa_max_sample_rate) %uHz without root privileges\n",
> +			if (oa_freq_hz > i915_oa_max_sample_rate && !perfmon_capable()) {
> +				DRM_DEBUG("OA exponent would exceed the max sampling frequency (sysctl dev.i915.oa_max_sample_rate) %uHz without CAP_SYS_PERFMON or CAP_SYS_ADMIN privileges\n",
>   					  i915_oa_max_sample_rate);
>   				return -EACCES;
>   			}
> @@ -3328,7 +3327,7 @@ int i915_perf_add_config_ioctl(struct drm_device *dev, void *data,
>   		return -EINVAL;
>   	}
>   
> -	if (i915_perf_stream_paranoid && !capable(CAP_SYS_ADMIN)) {
> +	if (i915_perf_stream_paranoid && !perfmon_capable()) {
>   		DRM_DEBUG("Insufficient privileges to add i915 OA config\n");
>   		return -EACCES;
>   	}
> @@ -3474,7 +3473,7 @@ int i915_perf_remove_config_ioctl(struct drm_device *dev, void *data,
>   		return -ENOTSUPP;
>   	}
>   
> -	if (i915_perf_stream_paranoid && !capable(CAP_SYS_ADMIN)) {
> +	if (i915_perf_stream_paranoid && !perfmon_capable()) {
>   		DRM_DEBUG("Insufficient privileges to remove i915 OA config\n");
>   		return -EACCES;
>   	}