ftrace/x86: Remove the complex ftrace NMI handling code

As ftrace function tracing would require modifying code that could
be executed in NMI context, which is not stopped with stop_machine(),
ftrace had to do a complex algorithm with various stages of setup
and memory barriers to make it work.

With the new breakpoint method, this is no longer required. The changes
to the code can be done without any problem in NMI context, as well as
without stop machine altogether. Remove the complex code as it is
no longer needed.

Also, a lot of the notrace annotations could be removed from the
NMI code as it is now safe to trace them. With the exception of
do_nmi itself, which does some special work to handle running in
the debug stack. The breakpoint method can cause NMIs to double
nest the debug stack if it's not setup properly, and that is done
in do_nmi(), thus that function must not be traced.

(Note the arch sh may want to do the same)

Cc: Paul Mundt <lethal@linux-sh.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 47acaf319165..eb1539eac393 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -84,7 +84,7 @@ __setup("unknown_nmi_panic", setup_unknown_nmi_panic);
 
 #define nmi_to_desc(type) (&nmi_desc[type])
 
-static int notrace __kprobes nmi_handle(unsigned int type, struct pt_regs *regs, bool b2b)
+static int __kprobes nmi_handle(unsigned int type, struct pt_regs *regs, bool b2b)
 {
         struct nmi_desc *desc = nmi_to_desc(type);
         struct nmiaction *a;
@@ -209,7 +209,7 @@ void unregister_nmi_handler(unsigned int type, const char *name)
 
 EXPORT_SYMBOL_GPL(unregister_nmi_handler);
 
-static notrace __kprobes void
+static __kprobes void
 pci_serr_error(unsigned char reason, struct pt_regs *regs)
 {
         pr_emerg("NMI: PCI system error (SERR) for reason %02x on CPU %d.\n",
@@ -236,7 +236,7 @@ pci_serr_error(unsigned char reason, struct pt_regs *regs)
         outb(reason, NMI_REASON_PORT);
 }
 
-static notrace __kprobes void
+static __kprobes void
 io_check_error(unsigned char reason, struct pt_regs *regs)
 {
         unsigned long i;
@@ -263,7 +263,7 @@ io_check_error(unsigned char reason, struct pt_regs *regs)
         outb(reason, NMI_REASON_PORT);
 }
 
-static notrace __kprobes void
+static __kprobes void
 unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
 {
         int handled;
@@ -305,7 +305,7 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
 static DEFINE_PER_CPU(bool, swallow_nmi);
 static DEFINE_PER_CPU(unsigned long, last_nmi_rip);
 
-static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
+static __kprobes void default_do_nmi(struct pt_regs *regs)
 {
         unsigned char reason = 0;
         int handled;