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Date: Thu, 25 Jan 2024 18:21:22 -0000
From: "tip-bot2 for Xin Li" <tip-bot2@linutronix.de>
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Subject: [tip: x86/fred] x86/fred: Add a machine check entry stub for FRED
Cc: Xin Li <xin3.li@intel.com>, Thomas Gleixner <tglx@linutronix.de>,
 Shan Kang <shan.kang@intel.com>, x86@kernel.org, linux-kernel@vger.kernel.org
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The following commit has been merged into the x86/fred branch of tip:

Commit-ID:     4aa4dce58fb07380c5a63c1993d0478f7ee195d1
Gitweb:        https://git.kernel.org/tip/4aa4dce58fb07380c5a63c1993d0478f7ee195d1
Author:        Xin Li <xin3.li@intel.com>
AuthorDate:    Tue, 05 Dec 2023 02:50:14 -08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 25 Jan 2024 19:10:32 +01:00

x86/fred: Add a machine check entry stub for FRED

Like #DB, when occurred on different ring level, i.e., from user or kernel
context, #MCE needs to be handled on different stack: User #MCE on current
task stack, while kernel #MCE on a dedicated stack.

This is exactly how FRED event delivery invokes an exception handler: ring
3 event on level 0 stack, i.e., current task stack; ring 0 event on the
#MCE dedicated stack specified in the IA32_FRED_STKLVLS MSR. So unlike IDT,
the FRED machine check entry stub doesn't do stack switch.

Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-26-xin3.li@intel.com

---
 arch/x86/kernel/cpu/mce/core.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index bc39252..04acdc3 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -46,6 +46,7 @@
 #include <linux/hardirq.h>
 #include <linux/kexec.h>
 
+#include <asm/fred.h>
 #include <asm/intel-family.h>
 #include <asm/processor.h>
 #include <asm/traps.h>
@@ -2166,6 +2167,31 @@ DEFINE_IDTENTRY_MCE_USER(exc_machine_check)
 	exc_machine_check_user(regs);
 	local_db_restore(dr7);
 }
+
+#ifdef CONFIG_X86_FRED
+/*
+ * When occurred on different ring level, i.e., from user or kernel
+ * context, #MCE needs to be handled on different stack: User #MCE
+ * on current task stack, while kernel #MCE on a dedicated stack.
+ *
+ * This is exactly how FRED event delivery invokes an exception
+ * handler: ring 3 event on level 0 stack, i.e., current task stack;
+ * ring 0 event on the #MCE dedicated stack specified in the
+ * IA32_FRED_STKLVLS MSR. So unlike IDT, the FRED machine check entry
+ * stub doesn't do stack switch.
+ */
+DEFINE_FREDENTRY_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
 #else
 /* 32bit unified entry point */
 DEFINE_IDTENTRY_RAW(exc_machine_check)