Messages in this thread | | | Date | Mon, 9 Nov 2015 09:52:23 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 4/4] x86/entry/64: Bypass enter_from_user_mode on non-context-tracking boots |
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* Andy Lutomirski <luto@kernel.org> wrote:
> On CONFIG_CONTEXT_TRACKING kernels that have context tracking > disabled at runtime (which includes most distro kernels), we still > have the overhead of a call to enter_from_user_mode in interrupt and > exception entries. > > If jump labels are available, this uses the jump label > infrastructure to skip the call. > > Signed-off-by: Andy Lutomirski <luto@kernel.org> > --- > arch/x86/entry/calling.h | 15 +++++++++++++++ > arch/x86/entry/entry_64.S | 8 ++------ > 2 files changed, 17 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h > index 3c71dd947c7b..271e30c585bc 100644 > --- a/arch/x86/entry/calling.h > +++ b/arch/x86/entry/calling.h > @@ -1,3 +1,5 @@ > +#include <linux/jump_label.h> > + > /* > > x86 function call convention, 64-bit: > @@ -232,3 +234,16 @@ For 32-bit we have the following conventions - kernel is built with > > #endif /* CONFIG_X86_64 */ > > +/* > + * This does 'call enter_from_user_mode' unless we can avoid it based on > + * kernel config or using the static jump infrastructure. > + */ > +.macro CALL_ENTER_FROM_USER_MODE > +#ifdef CONFIG_CONTEXT_TRACKING > +#ifdef HAVE_JUMP_LABEL > + STATIC_JUMP_IF_FALSE .Lafter_call_\@, context_tracking_enabled, def=0 > +#endif > + call enter_from_user_mode > +.Lafter_call_\@: > +#endif > +.endm > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > index f585df24ab3d..9b49b56efa29 100644 > --- a/arch/x86/entry/entry_64.S > +++ b/arch/x86/entry/entry_64.S > @@ -517,9 +517,7 @@ END(irq_entries_start) > */ > TRACE_IRQS_OFF > > -#ifdef CONFIG_CONTEXT_TRACKING > - call enter_from_user_mode > -#endif > + CALL_ENTER_FROM_USER_MODE > > 1: > /* > @@ -1058,9 +1056,7 @@ ENTRY(error_entry) > > .Lerror_entry_from_usermode_after_swapgs: > TRACE_IRQS_OFF > -#ifdef CONFIG_CONTEXT_TRACKING > - call enter_from_user_mode > -#endif > + CALL_ENTER_FROM_USER_MODE > ret
Yeah, so I only have a really minor syntactic nit abou tthis: it's OK to capitalize things when doing macros, but here I don't think capitalizing the called function name is good - I think the following would be more obvious:
CALL_enter_from_user_mode
this makes it really, really obvious (to me!) that this macro is a shortcut for:
call enter_from_user_mode
with some glue around it, and I could grep for 'enter_from_user_mode' immediately - while grepping for ENTER_FROM_USER_MODE would miss the called function.
Thanks,
Ingo
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