On Thu, 13 Apr 2017 17:53:55 -0500 Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > On x86-32, with CONFIG_FIRMWARE and multiple CPUs, if you enable > function graph tracing and then suspend to RAM, it will triple fault and > reboot when it resumes. > > The first fault happens when booting a secondary CPU: > > startup_32_smp() > load_ucode_ap() > prepare_ftrace_return() > ftrace_graph_is_dead() > (accesses 'kill_ftrace_graph') > > The early head_32.S code calls into load_ucode_ap(), which has an an > ftrace hook, so it calls prepare_ftrace_return(), which calls > ftrace_graph_is_dead(), which tries to access the global > 'kill_ftrace_graph' variable with a virtual address, causing a fault > because the CPU is still in real mode. > > The fix is to add a check in prepare_ftrace_return() to make sure it's > running in protected mode before continuing. The check makes sure the > stack pointer is a virtual kernel address. It's a bit of a hack, but > it's not very intrusive and it works well enough. > > For reference, here are a few other (more difficult) ways this could > have potentially been fixed: > > - Move startup_32_smp()'s call to load_ucode_ap() down to *after* paging > is enabled. (No idea what that would break.) > > - Track down load_ucode_ap()'s entire callee tree and mark all the > functions 'notrace'. (Probably not realistic.) > > - Pause graph tracing in ftrace_suspend_notifier_call() or bringup_cpu() > or __cpu_up(), and ensure that the pause facility can be queried from > real mode. > > Reported-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx> > Tested-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxx > Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> This is pretty much the same thing we were talking about before, right? If so, then: Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> if not, I need to spend more time reviewing it ;-) -- Steve > --- > v3: Added Tested-by: and Cc:stable tags > > arch/x86/kernel/ftrace.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index 9dd546b..a3adf1f 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -995,6 +995,18 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, > unsigned long return_hooker = (unsigned long) > &return_to_handler; > > + /* > + * When resuming from suspend-to-ram, this function can be indirectly > + * called from early CPU startup code while the CPU is in real mode, > + * which would fail miserably. Make sure the stack pointer is a > + * virtual address. > + * > + * This check isn't as accurate as virt_addr_valid(), but it should be > + * good enough for this purpose, and it's fast. > + */ > + if (unlikely((long)__builtin_frame_address(0) >= 0)) > + return; > + > if (unlikely(ftrace_graph_is_dead())) > return; > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
