* 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..e32206e09868 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 a55697d19824..9d34d3cfceb6 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -520,9 +520,7 @@ END(irq_entries_start)
> */
> TRACE_IRQS_OFF
>
> -#ifdef CONFIG_CONTEXT_TRACKING
> - call enter_from_user_mode
> -#endif
> + CALL_enter_from_user_mode
>
> 1:
> /*
> @@ -1066,9 +1064,7 @@ ENTRY(error_entry)
> * (which can take locks).
> */
> TRACE_IRQS_OFF
> -#ifdef CONFIG_CONTEXT_TRACKING
> - call enter_from_user_mode
> -#endif
> + CALL_enter_from_user_mode
> ret
>
> .Lerror_entry_done:
> --
> 2.5.0
>
hm, this patch does not apply to latest -tip:
patching file arch/x86/entry/entry_64.S
Hunk #1 FAILED at 520.
Hunk #2 FAILED at 1066.
2 out of 2 hunks FAILED -- rejects in file arch/x86/entry/entry_64.S
am I missing some dependency, or are they against an older tree?
Thanks,
Ingo
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