linux-kernel - Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play

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: <ZzWFP74YTGj5m6il@BLRRASHENOY1.amd.com>
Date: Thu, 14 Nov 2024 10:36:07 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	rafael.j.wysocki@...el.com, len.brown@...el.com,
	artem.bityutskiy@...ux.intel.com, dave.hansen@...ux.intel.com
Subject: Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer
 cpuidle_play_dead() over mwait_play_dead()

Hello Dave,
On Wed, Nov 13, 2024 at 08:14:08AM -0800, Dave Hansen wrote:
> On 11/13/24 03:41, Gautham R. Shenoy wrote:
> > +       /*
> > +        * This is ugly. But AMD processors don't prefer MWAIT based
> > +        * C-states when processors are offlined.
> > +        */
> > +       if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
> > +           boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
> > +               return -ENODEV;
> 
> Can we get an X86_FEATURE for this, please?  Either a positive one:
> 
> 	X86_FEATURE_MWAIT_OK_FOR_OFFLINE
> 
> or a negative one:
> 
> 	X86_FEATURE_MWAIT_BUSTED_FOR_OFFLINE
>

Sure. That makes sense.

> ... with better names.
> 
> Or even a helper.  Because if you add this AMD||HYGON check, it'll be at
> _least_ the second one of these for the same logical reason.

Fair enough. Will add that.

--
Thanks and Regards
gautham.