[PATCH v13 25/35] x86/fred: Add a machine check entry stub for FRED

Xin Li
2023-12-05T11:21:31Z

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.

Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---

Changes since v5:
* Disallow #DB inside #MCE for robustness sake (Peter Zijlstra).
---
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 1642018dd6c9..d524eb87f76c 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -53,6 +53,7 @@
#include <asm/mce.h>
#include <asm/msr.h>
#include <asm/reboot.h>
+#include <asm/fred.h>

#include "internal.h"

@@ -2150,6 +2151,31 @@ 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)
--
2.43.0