On Thu, Apr 13, 2017 at 07:02:36PM -0400, Steven Rostedt wrote: > 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? Yeah, the same patch from before, now with more tags! > If so, then: > > Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Thanks! -- Josh -- 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
