linux-kernel - [PATCH] x86, traps: install gates using IST after cpu

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Date:	Thu, 26 Feb 2015 14:15:15 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	<masami.hiramatsu.pt@...achi.com>, <rostedt@...dmis.org>
CC:	<mingo@...hat.com>, <hpa@...or.com>, <tglx@...utronix.de>,
	<x86@...nel.org>, <luto@...capital.net>, <oleg@...hat.com>,
	<dave.hansen@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
	<lizefan@...wei.com>
Subject: [PATCH] x86, traps: install gates using IST after cpu_init().

X86_TRAP_NMI, X86_TRAP_DF and X86_TRAP_MC use their own stack. Those
stacks are invalid until cpu_init() installs TSS.

This patch moves setting of the 3 gates after cpu_init().

Signed-off-by: Wang Nan <wangnan0@...wei.com>
---

If I understand correctly, logically speaking the original code is
incorrect.  However, there is no real bug caused by it for serval years.
I'm not sure whether this fix is practical or not. Fix them only for
logical correctness.

---
 arch/x86/kernel/traps.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4281988..cf7898e 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -962,7 +962,6 @@ void __init trap_init(void)
 #endif
 
 	set_intr_gate(X86_TRAP_DE, divide_error);
-	set_intr_gate_ist(X86_TRAP_NMI, &nmi, NMI_STACK);
 	/* int4 can be called from all */
 	set_system_intr_gate(X86_TRAP_OF, &overflow);
 	set_intr_gate(X86_TRAP_BR, bounds);
@@ -970,8 +969,6 @@ void __init trap_init(void)
 	set_intr_gate(X86_TRAP_NM, device_not_available);
 #ifdef CONFIG_X86_32
 	set_task_gate(X86_TRAP_DF, GDT_ENTRY_DOUBLEFAULT_TSS);
-#else
-	set_intr_gate_ist(X86_TRAP_DF, &double_fault, DOUBLEFAULT_STACK);
 #endif
 	set_intr_gate(X86_TRAP_OLD_MF, coprocessor_segment_overrun);
 	set_intr_gate(X86_TRAP_TS, invalid_TSS);
@@ -981,9 +978,6 @@ void __init trap_init(void)
 	set_intr_gate(X86_TRAP_SPURIOUS, spurious_interrupt_bug);
 	set_intr_gate(X86_TRAP_MF, coprocessor_error);
 	set_intr_gate(X86_TRAP_AC, alignment_check);
-#ifdef CONFIG_X86_MCE
-	set_intr_gate_ist(X86_TRAP_MC, &machine_check, MCE_STACK);
-#endif
 	set_intr_gate(X86_TRAP_XF, simd_coprocessor_error);
 
 	/* Reserve all the builtin and the syscall vector: */
@@ -1013,6 +1007,14 @@ void __init trap_init(void)
 	 */
 	cpu_init();
 
+	set_intr_gate_ist(X86_TRAP_NMI, &nmi, NMI_STACK);
+#ifndef CONFIG_X86_32
+	set_intr_gate_ist(X86_TRAP_DF, &double_fault, DOUBLEFAULT_STACK);
+#endif
+#ifdef CONFIG_X86_MCE
+	set_intr_gate_ist(X86_TRAP_MC, &machine_check, MCE_STACK);
+#endif
+
 	/*
 	 * X86_TRAP_DB and X86_TRAP_BP have been set
 	 * in early_trap_init(). However, DEBUG_STACK works only after
-- 
1.8.4

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