* Andy Lutomirski <l...@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 <l...@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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