linux-kernel - Re: [PATCH V2 08/23] perf/x86: Expose CPUID enumeration bits for arch LBR

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: <20200630163954.GY4817@hirez.programming.kicks-ass.net>
Date:   Tue, 30 Jun 2020 18:39:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     mingo@...hat.com, acme@...nel.org, tglx@...utronix.de,
        bp@...en8.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, dave.hansen@...el.com,
        yu-cheng.yu@...el.com, bigeasy@...utronix.de, gorcunov@...il.com,
        hpa@...or.com, alexey.budankov@...ux.intel.com, eranian@...gle.com,
        ak@...ux.intel.com, like.xu@...ux.intel.com,
        yao.jin@...ux.intel.com, wei.w.wang@...el.com
Subject: Re: [PATCH V2 08/23] perf/x86: Expose CPUID enumeration bits for
 arch LBR

On Tue, Jun 30, 2020 at 11:36:29AM -0400, Liang, Kan wrote:
> > Why keep the full CPUID leaf here? What's wrong with something like:
> > 
> > 	unsigned int	lbr_depth_mask:8;
> > 	unsigned int	lbr_deep_c_reset:1;
> > 	unsigned int	lbr_lip:1;
> > 	unsigned int	lbr_cpl:1;
> > 	unsigned int	lbr_filter:1;
> > 	unsigned int	lbr_call_stack:1;
> > 	unsigned int	lbr_mispred:1;
> > 	unsigned int	lbr_timed_lbr:1;
> > 	unsigned int	lbr_br_type:1;
> > 
> > That's only 2 bytes, instead of 24.
> 
> Yes, it can save the space.
> I will add some codes in patch 14 to initialize these items in
> intel_pmu_arch_lbr_init().

It also makes stuff like:

> +   if (!x86_pmu.lbr_ebx.split.lbr_cpl ||
> +       !x86_pmu.lbr_ebx.split.lbr_filter ||
> +       !x86_pmu.lbr_ebx.split.lbr_call_stack)

eminently more readable.