linux-kernel - [tip:ras/core] x86/mce: Fix thermal throttling reporting after kexec

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Message-ID: <tip-81ffdcdd97d94110627caa81c23d5d780083731d@git.kernel.org>
Date:	Wed, 21 Oct 2015 03:06:28 -0700
From:	tip-bot for Andi Kleen <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	peterz@...radead.org, bp@...e.de, ak@...ux.intel.com,
	torvalds@...ux-foundation.org, mingo@...nel.org,
	tglx@...utronix.de, tony.luck@...el.com, hpa@...or.com
Subject: [tip:ras/core] x86/mce:
  Fix thermal throttling reporting after kexec

Commit-ID:  81ffdcdd97d94110627caa81c23d5d780083731d
Gitweb:     http://git.kernel.org/tip/81ffdcdd97d94110627caa81c23d5d780083731d
Author:     Andi Kleen <ak@...ux.intel.com>
AuthorDate: Mon, 19 Oct 2015 11:17:48 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 21 Oct 2015 11:10:57 +0200

x86/mce: Fix thermal throttling reporting after kexec

The per CPU thermal vector init code checks if the thermal
vector is already installed and complains and bails out if it
is.

This happens after kexec, as kernel shut down does not clear the
thermal vector APIC register.

This causes two problems:

1. So we always do not fully initialize thermal reports after
   kexec. The CPU is still likely initialized, as the previous
   kernel should have done it. But we don't set up the software
   pointer to the thermal vector, so reporting may end up with a
   unknown thermal interrupt message.

2. Also it complains for every logical CPU, even though the
   value is actually derived from BP only.

The problem is that we end up with one message per CPU, so on
larger systems it becomes very noisy and messes up the otherwise
nicely formatted CPU bootup numbers in the kernel log.

Just remove the check. I checked the code and there's no valid
code paths where the thermal init code for a CPU could be called
multiple times.

Why the kernel does not clean up this value on shutdown:

The thermal monitoring is controlled per logical CPU thread.
Normal shutdown code is just running on one CPU. To disable it
we would need a broadcast NMI to all CPUs on shut down. That's
overkill for this. So we just ignore it after kexec.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Tony Luck <tony.luck@...el.com>
Cc: linux-edac <linux-edac@...r.kernel.org>
Link: http://lkml.kernel.org/r/1445246268-26285-9-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/mcheck/therm_throt.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
index 1af51b1..2c5aaf8 100644
--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -503,14 +503,6 @@ void intel_init_thermal(struct cpuinfo_x86 *c)
 		return;
 	}

-	/* Check whether a vector already exists */
-	if (h & APIC_VECTOR_MASK) {
-		printk(KERN_DEBUG
-		       "CPU%d: Thermal LVT vector (%#x) already installed\n",
-		       cpu, (h & APIC_VECTOR_MASK));
-		return;
-	}
-
 	/* early Pentium M models use different method for enabling TM2 */
 	if (cpu_has(c, X86_FEATURE_TM2)) {
 		if (c->x86 == 6 && (c->x86_model == 9 || c->x86_model == 13)) {
--
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