Messages in this thread | | | Date | Thu, 24 Oct 2019 01:31:38 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch V2 08/17] x86/entry: Move syscall irq tracing to C code |
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On Wed, 23 Oct 2019, Andy Lutomirski wrote: > On Wed, Oct 23, 2019 at 2:30 PM Andy Lutomirski <luto@kernel.org> wrote: > > > > On Wed, Oct 23, 2019 at 5:31 AM Thomas Gleixner <tglx@linutronix.de> wrote: > > > > > > Interrupt state tracing can be safely done in C code. The few stack > > > operations in assembly do not need to be covered. > > > > > > Remove the now pointless indirection via .Lsyscall_32_done and jump to > > > swapgs_restore_regs_and_return_to_usermode directly. > > > > This doesn't look right. > > > > > #define SYSCALL_EXIT_WORK_FLAGS \ > > > @@ -279,6 +282,9 @@ static void syscall_slow_exit_work(struc > > > { > > > struct thread_info *ti; > > > > > > + /* User to kernel transition disabled interrupts. */ > > > + trace_hardirqs_off(); > > > + > > > > So you just traced IRQs off, but... > > > > > enter_from_user_mode(); > > > local_irq_enable(); > > > > Now they're on and traced on again? > > > > I also don't see how your patch handles the fastpath case. > > > > How about the attached patch instead? > > Ignore the attached patch. You have this in your > do_exit_to_usermode() later in the series. But I'm still quite > confused by this patch.
What's confusing you? It basically does:
ENTRY(syscall/int80)
- TRACE_IRQS_OFF call C-syscall*() - TRACE_IRQS_ON/IRET
and
C-syscall*()
+ trace_hardirqs_off() <- first action .... prepare_exit_to_usermode() <- last action return
and
prepare_exit_to_usermode() .... + trace_hardirqs_on() <- last action return
So this is exactly the same as the ASM today.
The only change is that I made it do unconditionally trace_hardirqs_on() for consistency reasons.
I tried to split it into bits and pieces, but failed to come up with something sensible. Let me try again tomorrow.
Thanks,
tglx
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