From: Borislav Petkov <bp@alien8.de>
To: Jason Baron <jasonbaron0@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>,
Thomas Gleixner <tglx@linutronix.de>,
Mikulas Patocka <mpatocka@redhat.com>,
Paul Mackerras <paulus@samba.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Kees Cook <keescook@chromium.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Vince Weaver <vince@deater.net>,
"hillf.zj" <hillf.zj@alibaba-inc.com>,
Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: Kernel broken on processors without performance counters
Date: Wed, 22 Jul 2015 06:24:03 +0200 [thread overview]
Message-ID: <20150722042403.GA6345@nazgul.tnic> (raw)
In-Reply-To: <55AE9471.1000601@gmail.com>
On Tue, Jul 21, 2015 at 02:50:25PM -0400, Jason Baron wrote:
> hmmm...so this is a case where need to the default the branch
> to the out-of-line branch at boot. That is, we can't just enable
> the out-of-line branch at boot time, b/c it might be too late at
> that point? IE native_sched_clock() gets called very early?
Well, even the layout is wrong here. The optimal thing would be to have:
NOP
rdtsc
unlikely:
/* read jiffies */
at build time. And then at boot time, patch in the JMP over the NOP on
!use_tsc boxes. And RDTSC works always, no matter how early.
I'm fairly sure we can do that now with alternatives instead of jump
labels.
The problem currently is that the 5-byte NOP gets patched in with a JMP
so we have an unconditional forwards JMP to the RDTSC.
Now I'd put my money on most arches handling NOPs better then
unconditional JMPs and this is a hot path...
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
next prev parent reply other threads:[~2015-07-22 4:24 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-08 15:17 Mikulas Patocka
2015-07-08 16:07 ` Peter Zijlstra
2015-07-08 16:54 ` Mikulas Patocka
2015-07-09 17:23 ` [PATCH] x86: Fix static_key in load_mm_cr4() Peter Zijlstra
2015-07-09 19:11 ` Mikulas Patocka
2015-07-10 8:27 ` [tip:perf/urgent] x86, perf: Fix static_key bug " tip-bot for Peter Zijlstra
2015-07-08 17:37 ` Kernel broken on processors without performance counters Andy Lutomirski
2015-07-08 20:04 ` Jason Baron
2015-07-09 0:36 ` Andy Lutomirski
2015-07-10 14:13 ` Peter Zijlstra
2015-07-10 15:29 ` Jason Baron
2015-07-21 8:21 ` Peter Zijlstra
2015-07-21 15:43 ` Thomas Gleixner
2015-07-21 15:49 ` Peter Zijlstra
2015-07-21 15:51 ` Andy Lutomirski
2015-07-21 16:12 ` Peter Zijlstra
2015-07-21 16:57 ` Jason Baron
2015-07-23 14:54 ` Steven Rostedt
2015-07-21 18:15 ` Borislav Petkov
2015-07-21 18:50 ` Jason Baron
2015-07-21 18:54 ` Andy Lutomirski
2015-07-21 19:00 ` Valdis.Kletnieks
2015-07-21 19:29 ` Andy Lutomirski
2015-07-21 23:49 ` Valdis.Kletnieks
2015-07-22 4:24 ` Borislav Petkov [this message]
2015-07-22 17:06 ` Jason Baron
2015-07-23 10:42 ` Peter Zijlstra
2015-07-23 10:53 ` Borislav Petkov
2015-07-23 14:19 ` Jason Baron
2015-07-23 14:33 ` Peter Zijlstra
2015-07-23 14:49 ` Peter Zijlstra
2015-07-23 19:14 ` Jason Baron
2015-07-24 10:56 ` Peter Zijlstra
2015-07-24 12:36 ` Peter Zijlstra
2015-07-24 14:15 ` Jason Baron
2015-07-23 14:58 ` Peter Zijlstra
2015-07-23 15:34 ` Steven Rostedt
2015-07-23 17:08 ` Peter Zijlstra
2015-07-23 17:18 ` Steven Rostedt
2015-07-23 17:33 ` Jason Baron
2015-07-23 18:12 ` Steven Rostedt
2015-07-23 19:02 ` Peter Zijlstra
2015-07-23 17:35 ` Andy Lutomirski
2015-07-23 17:54 ` Borislav Petkov
2015-07-23 19:02 ` Peter Zijlstra
2015-07-24 5:29 ` Borislav Petkov
2015-07-24 10:36 ` Peter Zijlstra
2015-07-22 20:43 ` Mikulas Patocka
2015-07-21 15:53 ` Thomas Gleixner
2015-07-21 15:54 ` Peter Zijlstra
2015-07-09 17:11 ` Peter Zijlstra
2015-07-09 19:15 ` Jason Baron
2015-07-14 9:35 ` Borislav Petkov
2015-07-14 12:43 ` Mikulas Patocka
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