[RFC][PATCH 4/4] x86/entry, mce: Disallow #DB during #MC

[Peter Zijlstra]

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

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
 arch/x86/kernel/cpu/mce/core.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- 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_
 /* MCE hit kernel mode */
 DEFINE_IDTENTRY_MCE(exc_machine_check)
 {
+       unsigned long dr7;
+
+       local_db_save(&dr7);
        exc_machine_check_kernel(regs);
+       local_db_restore(dr7);
 }
 
 /* The user mode variant. */
 DEFINE_IDTENTRY_MCE_USER(exc_machine_check)
 {
+       unsigned long dr7;
+
+       local_db_save(&dr7);
        exc_machine_check_user(regs);
+       local_db_restore(dr7);
 }
 #else
 /* 32bit unified entry point */
 DEFINE_IDTENTRY_MCE(exc_machine_check)
 {
+       unsigned long dr7;
+
+       local_db_save(&dr7);
        if (user_mode(regs))
                exc_machine_check_user(regs);
        else
                exc_machine_check_kernel(regs);
+       local_db_restore(dr7);
 }
 #endif