linux-kernel - Re: [PATCH 3/3] perf, x86: Add INST

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

Message-ID: <20150323093854.GA24993@gmail.com>
Date:	Mon, 23 Mar 2015 10:38:54 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	peterz@...radead.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 3/3] perf, x86: Add INST_RETIRED.ALL workarounds


* Andi Kleen <andi@...stfloor.org> wrote:

> From: Andi Kleen <ak@...ux.intel.com>
> 
> On Broadwell INST_RETIRED.ALL cannot be used with any period
> that doesn't have the lowest 6 bits cleared. And the period
> should not be smaller than 128.

Sloppy changelog: a most basic question is not answered by the 
changelog: what happens in practice when the period is set to a 
smaller value than 128?

> +/*
> + * Broadwell:
> + * The INST_RETIRED.ALL period always needs to have lowest
> + * 6bits cleared (BDM57). It shall not use a period smaller
> + * than 100 (BDM11). We combine the two to enforce
> + * a min-period of 128.
> + */

Sloppy comment: that's not what we do:

> +static unsigned bdw_limit_period(struct perf_event *event, unsigned left)
> +{
> +	if ((event->hw.config & INTEL_ARCH_EVENT_MASK) ==
> +			X86_CONFIG(.event=0xc0, .umask=0x01)) {
> +		if (left < 128)
> +			left = 128;
> +		left &= ~0x3fu;
> +	}
> +	return left;

We enforce a minimum period of 128 and round the requested period to 
64.

I think in this case it would be useful to tooling if we updated the 
syscall attribute with the real period value that was used, to not 
skew tooling output.

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/