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    SubjectRe: [PATCH 3/3] jump_label: make initial NOP patching the special case
    On Wed, Jun 08, 2022 at 12:45:12PM +0200, Ard Biesheuvel wrote:
    > Instead of defaulting to patching NOP opcodes at init time, and leaving
    > it to the architectures to override this if this is not needed, switch
    > to a model where doing nothing is the default. This is the common case
    > by far, as only MIPS requires NOP patching at init time. On all other
    > architectures, the correct encodings are emitted by the compiler and so
    > no initial patching is needed.
    >
    > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
    > ---
    > Documentation/staging/static-keys.rst | 3 ---
    > arch/arc/kernel/jump_label.c | 13 -------------
    > arch/arm/kernel/jump_label.c | 6 ------
    > arch/arm64/kernel/jump_label.c | 11 -----------
    > arch/mips/include/asm/jump_label.h | 2 ++
    > arch/parisc/kernel/jump_label.c | 11 -----------
    > arch/riscv/kernel/jump_label.c | 12 ------------
    > arch/s390/kernel/jump_label.c | 5 -----
    > arch/x86/kernel/jump_label.c | 13 -------------
    > kernel/jump_label.c | 14 +++-----------
    > 10 files changed, 5 insertions(+), 85 deletions(-)

    I have one minor comment below, but either way this is a nice cleanup (and I'm
    always happy to see __weak functions disappear), so FWIW:

    Acked-by: Mark Rutland <mark.rutland@arm.com>

    [...]

    > diff --git a/kernel/jump_label.c b/kernel/jump_label.c
    > index b1ac2948be79..ff8576c00893 100644
    > --- a/kernel/jump_label.c
    > +++ b/kernel/jump_label.c
    > @@ -332,17 +332,9 @@ static int __jump_label_text_reserved(struct jump_entry *iter_start,
    > return 0;
    > }
    >
    > -/*
    > - * Update code which is definitely not currently executing.
    > - * Architectures which need heavyweight synchronization to modify
    > - * running code can override this to make the non-live update case
    > - * cheaper.
    > - */
    > -void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
    > - enum jump_label_type type)
    > -{
    > - arch_jump_label_transform(entry, type);
    > -}
    > +#ifndef arch_jump_label_transform_static
    > +#define arch_jump_label_transform_static(entry, type)
    > +#endif

    It might be slightly better to make this a static inline stub so that we always
    get the compiler to type-check it, e.g.

    | #ifndef arch_jump_label_transform_static
    | static inline void arch_jump_label_transform_static(struct jump_entry *entry,
    | enum jump_label_type type)
    | {
    | /* nothing to do on most architectures */
    | }
    | #define arch_jump_label_transform_static arch_jump_label_transform_static
    | #endif

    Mark.

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