linux-kernel - Re: [tip:x86/idle] x86, idle: Use static_cpu_has() for CLFLUSH workaround, add barriers

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]

Date:	Thu, 19 Dec 2013 22:55:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	hpa@...or.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	hpa@...ux.intel.com, len.brown@...el.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/idle] x86, idle: Use static_cpu_has() for CLFLUSH
 workaround, add barriers

On Thu, Dec 19, 2013 at 09:40:51PM +0100, Ingo Molnar wrote:
> > +		if (static_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
> > +			mb();
> >  			clflush((void *)&current_thread_info()->flags);
> > +			mb();
> > +		}

>  	if (!current_set_polling_and_test()) {
>  		if (static_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
> -			mb();
> +			/*
> +			 * There's no need for an extra barrier here: current_set_polling_and_test()
> +			 * already has an smp_mb() after ->flags gets modified, see sched.h.
> +			 */
>  			clflush((void *)&current_thread_info()->flags);
>  			mb();
>  		}

So almost, except that smp_mb() will disappear on an UP kernel whereas
this errata might just always need the MFENCE.

Then again, you'd be a pretty big nutter to run an UP kernel on an EX
part.
--
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/