linux-kernel - [tip: x86/entry] x86/entry, mce: Disallow #DB during #MC

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Date:   Sat, 30 May 2020 09:57:20 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/entry] x86/entry, mce: Disallow #DB during #MC

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     ff98610a03285516b578821549973f969118d6a3
Gitweb:        https://git.kernel.org/tip/ff98610a03285516b578821549973f969118d6a3
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Fri, 29 May 2020 23:27:35 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Sat, 30 May 2020 10:00:08 +02:00

x86/entry, mce: Disallow #DB during #MC

#MC is fragile as heck, don't tempt fate.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/20200529213321.131187767@infradead.org

---
 arch/x86/kernel/cpu/mce/core.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 068e6ca..be49926 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1943,22 +1943,34 @@ static __always_inline void exc_machine_check_user(struct pt_regs *regs)
 /* MCE hit kernel mode */
 DEFINE_IDTENTRY_MCE(exc_machine_check)
 {
+	unsigned long dr7;
+
+	dr7 = local_db_save();
 	exc_machine_check_kernel(regs);
+	local_db_restore(dr7);
 }
 
 /* The user mode variant. */
 DEFINE_IDTENTRY_MCE_USER(exc_machine_check)
 {
+	unsigned long dr7;
+
+	dr7 = local_db_save();
 	exc_machine_check_user(regs);
+	local_db_restore(dr7);
 }
 #else
 /* 32bit unified entry point */
 DEFINE_IDTENTRY_MCE(exc_machine_check)
 {
+	unsigned long dr7;
+
+	dr7 = local_db_save();
 	if (user_mode(regs))
 		exc_machine_check_user(regs);
 	else
 		exc_machine_check_kernel(regs);
+	local_db_restore(dr7);
 }
 #endif