linux-kernel - [PATCH 2/2] x86: Stop Intel PT before kdump starts

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Date:	Wed, 28 Oct 2015 17:25:48 +0900
From:	Takao Indoh <indou.takao@...fujitsu.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Vivek Goyal <vgoyal@...hat.com>
CC:	<linux-kernel@...r.kernel.org>, <x86@...nel.org>
Subject: [PATCH 2/2] x86: Stop Intel PT before kdump starts

This patch stops Intel PT logging and saves its registers in the memory
before kdump is started. This feature is needed to prevent Intel PT from
overwrite its log buffer after panic, and saved registers are needed to
find the last position where Intel PT wrote data. After crash dump is
captured by kdump, user can retrieve the log buffer from vmcore and use
it to investigate kernel behavior.

Signed-off-by: Takao Indoh <indou.takao@...fujitsu.com>
---
 arch/x86/kernel/crash.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 74ca2fe..5f383d2 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -35,6 +35,7 @@
 #include <asm/cpu.h>
 #include <asm/reboot.h>
 #include <asm/virtext.h>
+#include <asm/intel_pt.h>
 
 /* Alignment required for elf header segment */
 #define ELF_CORE_HEADER_ALIGN   4096
@@ -127,6 +128,11 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
 	cpu_emergency_vmxoff();
 	cpu_emergency_svm_disable();
 
+	/*
+	 * Disable Intel PT to stop its logging
+	 */
+	cpu_emergency_stop_pt();
+
 	disable_local_APIC();
 }
 
@@ -172,6 +178,11 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 	cpu_emergency_vmxoff();
 	cpu_emergency_svm_disable();
 
+	/*
+	 * Disable Intel PT to stop its logging
+	 */
+	cpu_emergency_stop_pt();
+
 #ifdef CONFIG_X86_IO_APIC
 	/* Prevent crash_kexec() from deadlocking on ioapic_lock. */
 	ioapic_zap_locks();
-- 
1.7.1


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