linux-kernel - Re: [PATCH 08/10] perf/core: Add PERF_AUX_FLAG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <72e0e51c-9abf-641f-f13e-ee07e12c02c1@arm.com>
Date:   Fri, 31 Mar 2017 17:44:23 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     mark.rutland@....com, robh@...nel.org, kim.phillips@....com,
        mathieu.poirier@...aro.org, pawel.moll@....com,
        suzuki.poulose@....com, marc.zyngier@....com,
        linux-kernel@...r.kernel.org, alexander.shishkin@...ux.intel.com,
        peterz@...radead.org, mingo@...hat.com, tglx@...utronix.de,
        alex.bennee@...aro.org, christoffer.dall@...aro.org
Subject: Re: [PATCH 08/10] perf/core: Add PERF_AUX_FLAG_COLLISION to report
 colliding samples

Hi Will,

On 27/01/17 18:07, Will Deacon wrote:
> The ARM SPE architecture permits an implementation to ignore a sample
> if the sample is due to be taken whilst another sample is already being
> produced. In this case, it is desirable to report the collision to
> userspace, as they may want to lower the sample period.
> 
> This patch adds a PERF_AUX_FLAG_COLLISION flag, so that such events can
> be relayed to userspace.
> 
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  include/uapi/linux/perf_event.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index c66a485a24ac..68a4e542968e 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -885,6 +885,7 @@ enum perf_callchain_context {
>   */
>  #define PERF_AUX_FLAG_TRUNCATED		0x01	/* record was truncated to fit */
>  #define PERF_AUX_FLAG_OVERWRITE		0x02	/* snapshot from overwrite mode */
> +#define PERF_AUX_FLAG_COLLISION		0x03	/* sample collided with another */

Does COLLISION really represent the combination of both TRUNCATED and
OVERWRITE, or does that want to be 0x04? (The way they get ORed together
at one point in the following patch makes me suspicious.)

Robin.

>  
>  #define PERF_FLAG_FD_NO_GROUP		(1UL << 0)
>  #define PERF_FLAG_FD_OUTPUT		(1UL << 1)
>