linux-kernel - Re: [PATCH V2 1/8] perf: Add PERF_SAMPLE_PHYS

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Message-ID: <20160119163020.GJ6344@twins.programming.kicks-ass.net>
Date:	Tue, 19 Jan 2016 17:30:20 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	kan.liang@...el.com
Cc:	acme@...nel.org, eranian@...gle.com, ak@...ux.intel.com,
	jolsa@...nel.org, namhyung@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 1/8] perf: Add PERF_SAMPLE_PHYS_ADDR

On Thu, Jan 07, 2016 at 08:30:33AM -0500, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> For understanding how the workload maps to memory channels and hardware
> behavior, it's useful to collect address maps with physical addresses.
> This is not intended for detecting page sharing (which can be already
> done using the mmap inode), but for lower level hardware behavior
> studies.

This patch set completely lacks any useful example for why we should
entertain this.

> @@ -8269,6 +8275,11 @@ SYSCALL_DEFINE5(perf_event_open,
>  			return -EINVAL;
>  	}
>  
> +	/* Only privileged users can get kernel addresses */
> +	if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
> +	    !capable(CAP_SYS_ADMIN))
> +		return -EACCES;
> +

should that not also include a perf_paranoid_kernel() test?