From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753138AbbJUR6M (ORCPT ); Wed, 21 Oct 2015 13:58:12 -0400 Received: from mail.skyhub.de ([78.46.96.112]:44222 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752002AbbJUR6J (ORCPT ); Wed, 21 Oct 2015 13:58:09 -0400 Date: Wed, 21 Oct 2015 19:58:03 +0200 From: Borislav Petkov To: Peter Zijlstra Cc: x86-ml , Peter Zijlstra , Andy Lutomirski , Steven Rostedt , lkml Subject: Re: [RFC PATCH] x86: Kill notsc Message-ID: <20151021175803.GF3575@pd.tnic> References: <20151018142007.GA11294@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20151018142007.GA11294@pd.tnic> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 18, 2015 at 04:20:07PM +0200, Borislav Petkov wrote: > Ok, > > let's try this and see where it takes us. Patch has been only lightly > tested in kvm - I'll hammer on it for real once we agree about the > general form. > > Aanyway, this patch is something Peter and I have been talking about on > IRC a couple of times already. I finally found some free time to poke at > it, here's the result. > > Thoughts? > > --- > > Kill "notsc" cmdline option and all the glue around it. The two boxes > worldwide which don't have a TSC should disable X86_TSC. Thus, make > native_sched_clock() use TSC unconditionally, even if the TSC is > unstable because that's fine there. This gets rid of the static key > too and makes the function even simpler and faster, which is a Good > Thing(tm). > > The jiffies-fallback is for the !X86_TSC case. > > Signed-off-by: Borislav Petkov > --- > Documentation/kernel-parameters.txt | 2 - > Documentation/x86/x86_64/boot-options.txt | 5 --- > arch/x86/include/asm/tsc.h | 3 +- > arch/x86/kernel/apic/apic.c | 2 +- > arch/x86/kernel/tsc.c | 74 ++++++++----------------------- > 5 files changed, 21 insertions(+), 65 deletions(-) ... > +#ifdef CONFIG_X86_TSC > + /* return the value in ns */ > + return cycles_2_ns(rdtsc()); > +#else Ok, we have a problem here: See the splat below. On the init path start_kernel |-> sched_init |-> init_idle we're calling sched_clock() which does the cycles_2_ns() thing. However, that cycles_2_ns() thing gets called only in tsc_init() which comes later in start_kernel(). Which means, data in this line ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, data->cyc2ns_shift); is NULL. Now, the question is, can I push only the cyc2ns_init() call up, before sched_init()? I mean, it dummy initializes only the per-cpu variable and tsc_init() will correct it anyway, as the comment says: /* * Secondary CPUs do not run through tsc_init(), so set up * all the scale factors for all CPUs, assuming the same * speed as the bootup CPU. (cpufreq notifiers will fix this * up if their speed diverges) */ for_each_possible_cpu(cpu) { cyc2ns_init(cpu); set_cyc2ns_scale(cpu_khz, cpu); } Thoughts? [ 0.000000] BUG: unable to handle kernel NULL pointer dereference at (null) [ 0.000000] IP: [] native_sched_clock+0x2d/0x90 [ 0.000000] PGD 0 [ 0.000000] Oops: 0000 [#1] PREEMPT SMP [ 0.000000] Modules linked in: [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.3.0-rc6+ #4 [ 0.000000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014 [ 0.000000] task: ffffffff819f7500 ti: ffffffff819e8000 task.ti: ffffffff819e8000 [ 0.000000] RIP: 0010:[] [] native_sched_clock+0x2d/0x90 [ 0.000000] RSP: 0000:ffffffff819ebee0 EFLAGS: 00010046 [ 0.000000] RAX: 0000000129f79c5a RBX: ffff88007b7d5c00 RCX: 0000000000000000 [ 0.000000] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff819f76e0 [ 0.000000] RBP: ffffffff819ebee0 R08: 0000000000000001 R09: 0000000000000000 [ 0.000000] R10: 0000000000000001 R11: ffffffff819f7500 R12: 0000000000000000 [ 0.000000] R13: 0000000000000000 R14: ffffffff819f7b30 R15: ffffffff819f7500 [ 0.000000] FS: 0000000000000000(0000) GS:ffff88007b600000(0000) knlGS:0000000000000000 [ 0.000000] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 0.000000] CR2: 0000000000000000 CR3: 00000000019f2000 CR4: 00000000000406b0 [ 0.000000] Stack: [ 0.000000] ffffffff819ebf28 ffffffff8108622f 0000000000000000 0000000000000086 [ 0.000000] ffffffff819f7500 0000000000000008 0000000000000008 00000000001d5c00 [ 0.000000] ffffffff0000ffff ffffffff819ebf58 ffffffff81cace4f ffffffffffffffff [ 0.000000] Call Trace: [ 0.000000] [] init_idle+0x13f/0x2d0 [ 0.000000] [] sched_init+0x304/0x345 [ 0.000000] [] start_kernel+0x25e/0x417 [ 0.000000] [] x86_64_start_reservations+0x2a/0x2c [ 0.000000] [] x86_64_start_kernel+0x168/0x176 [ 0.000000] Code: 89 e5 48 83 e4 f0 0f 31 48 c1 e2 20 48 09 d0 65 ff 05 88 dd ff 7e 65 48 8b 35 e0 5b 1c 7f 65 48 8b 15 e0 5b 1c 7f 48 39 d6 75 2c <8b> 16 8b 4e 04 48 f7 e2 48 0f ad d0 48 d3 ea f6 c1 40 48 0f 45 [ 0.000000] RIP [] native_sched_clock+0x2d/0x90 [ 0.000000] RSP [ 0.000000] CR2: 0000000000000000 [ 0.000000] ---[ end trace aff58b1304cfecf1 ]--- [ 0.000000] Kernel panic - not syncing: Attempted to kill the idle task! [ 0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.