[RFC] #MC mess

Borislav Petkov
2020-02-18T17:31:57Z

Ok,

so Peter raised this question on IRC today, that the #MC handler needs
to disable all kinds of tracing/kprobing and etc exceptions happening
while handling an #MC. And I guess we can talk about supporting some
exceptions but #MC is usually nasty enough to not care about tracing
when former happens.

So how about this trivial first stab of using the big hammer and simply
turning off stuff? The nmi_enter()/nmi_exit() thing still needs debating
because ist_enter() already does rcu_nmi_enter() and I'm not sure
whether any of the context tracking would still be ok with that.

Anything else I'm missing? It is likely...

Thx.

---
diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 2c4f949611e4..6dff97c53310 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1214,7 +1214,7 @@ static void __mc_scan_banks(struct mce *m, struct mce *final,
* MCE broadcast. However some CPUs might be broken beyond repair,
* so be always careful when synchronizing with others.
*/
-void do_machine_check(struct pt_regs *regs, long error_code)
+void notrace do_machine_check(struct pt_regs *regs, long error_code)
{
DECLARE_BITMAP(valid_banks, MAX_NR_BANKS);
DECLARE_BITMAP(toclear, MAX_NR_BANKS);
@@ -1251,6 +1251,10 @@ void do_machine_check(struct pt_regs *regs, long error_code)
if (__mc_check_crashing_cpu(cpu))
return;

+ hw_breakpoint_disable();
+ static_key_disable(&__tracepoint_read_msr.key);
+ tracing_off();
+
ist_enter(regs);

this_cpu_inc(mce_exception_count);
@@ -1360,6 +1364,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
ist_exit(regs);
}
EXPORT_SYMBOL_GPL(do_machine_check);
+NOKPROBE_SYMBOL(do_machine_check);

#ifndef CONFIG_MEMORY_FAILURE
int memory_failure(unsigned long pfn, int flags)

--
Regards/Gruss,
Boris.