linux-kernel - [RFC PATCH V2 6/7] x86/entry: is_debug

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Date:   Tue, 26 May 2020 01:42:20 +0000
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Changbin Du <changbin.du@...el.com>,
        Martin Molnar <martin.molnar.programming@...il.com>
Subject: [RFC PATCH V2 6/7] x86/entry: is_debug_stack() don't check of DB1 stack

IST-shift code is removed from entry code, #DB will not
at DB1 stack. So we remove the check of DB1 stack in
is_debug_stack().

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/kernel/nmi.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 1c58454ac5fb..2f463f5880c6 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -500,15 +500,10 @@ static noinstr bool is_debug_stack(unsigned long addr)
 {
 	struct cea_exception_stacks *cs = __this_cpu_read(cea_exception_stacks);
 	unsigned long top = CEA_ESTACK_TOP(cs, DB);
-	unsigned long bot = CEA_ESTACK_BOT(cs, DB1);
+	unsigned long bot = CEA_ESTACK_BOT(cs, DB);
 
 	if (__this_cpu_read(debug_stack_usage))
 		return true;
-	/*
-	 * Note, this covers the guard page between DB and DB1 as well to
-	 * avoid two checks. But by all means @addr can never point into
-	 * the guard page.
-	 */
 	return addr >= bot && addr < top;
 }
 #endif
-- 
2.20.1