linux-kernel - Re: [tip:x86/urgent] x86/entry/32: Add an ASM_CLAC to entry_SYSENTER

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: <1456391333.3709.8.camel@gmail.com>
Date:	Thu, 25 Feb 2016 10:08:53 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Brian Gerst <brgerst@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [tip:x86/urgent] x86/entry/32: Add an ASM_CLAC to
 entry_SYSENTER_32

On Thu, 2016-02-25 at 09:40 +0100, Ingo Molnar wrote:
> * Mike Galbraith <umgwanakikbuti@...il.com> wrote:
> 
> > On Thu, 2016-02-25 at 09:14 +0100, Ingo Molnar wrote:
> > 
> > > But but ... 'context tracking' is not really something that a regular distro 
> > > kernel cares about much - it's a nohz-full special AFAICS.
> 
> Let me qualify that: with the timer code maintenance hat on I really love all nohz 
> variants (the deeper the better), but now I have my x86 maintainer hat on, and as 
> such I'm really annoyed at those nohz folks adding overhead to the syscall hot 
> path! ;-)
> 
> > (psst.. distros are shipping it)
> 
> Yeah, indeed, Fedora does - but AFAICS:
> 
>  fomalhaut:~> grep NO_HZ /boot/config-4.1.13-100.fc21.x86_64 
>  CONFIG_NO_HZ_COMMON=y
>  # CONFIG_NO_HZ_IDLE is not set
>  CONFIG_NO_HZ_FULL=y
>  # CONFIG_NO_HZ_FULL_ALL is not set
>  # CONFIG_NO_HZ_FULL_SYSIDLE is not set
>  CONFIG_NO_HZ=y
>  CONFIG_RCU_FAST_NO_HZ=y
> 
> ... which won't result in actual full-nohz CPUs unless you boot it with a special 
> boot parameter, right?

Yeah, you have to manually enable it unless you (in a suicidal moment)
enable CONFIG_NO_HZ_FULL_ALL.

> What is the easiest way to query which/how many CPUs are in nohz-full mode and do 
> context tracking? I somehow thought /proc/timer_* had that info, but that does not 
> appear to be the case.

/sys/devices/system/cpu/nohz_full

	-Mike