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Date:   Sat, 4 Jul 2020 13:22:56 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Emil Renner Berthing <kernel@...il.dk>
Cc:     linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] riscv: Add jump-label implementation

On Fri, 3 Jul 2020 at 17:43, Emil Renner Berthing <kernel@...il.dk> wrote:
>
> On Thu, 2 Jul 2020 at 22:07, Emil Renner Berthing <kernel@...il.dk> wrote:
> >
> > Add basic jump-label implementation heavily based
> > on the ARM64 version.
> >
> > Tested on the HiFive Unleashed.
> >
> > Signed-off-by: Emil Renner Berthing <kernel@...il.dk>
> > ---
> >
> > This seems to work on my HiFive Unleashed. At least boots, runs fine
> > and the static key self-tests doesn't complain, but I'm sure I've missed
> > something, so I'm sending this as an RFC.
> >
> > /Emil
> >
> >  .../core/jump-labels/arch-support.txt         |  2 +-
> >  arch/riscv/Kconfig                            |  2 +
> >  arch/riscv/include/asm/jump_label.h           | 59 +++++++++++++++++++
> >  arch/riscv/kernel/Makefile                    |  2 +
> >  arch/riscv/kernel/jump_label.c                | 44 ++++++++++++++
> >  5 files changed, 108 insertions(+), 1 deletion(-)
> >  create mode 100644 arch/riscv/include/asm/jump_label.h
> >  create mode 100644 arch/riscv/kernel/jump_label.c
> >
> > diff --git a/Documentation/features/core/jump-labels/arch-support.txt b/Documentation/features/core/jump-labels/arch-support.txt
> > index 632a1c7aefa2..760243d18ed7 100644
> > --- a/Documentation/features/core/jump-labels/arch-support.txt
> > +++ b/Documentation/features/core/jump-labels/arch-support.txt
> > @@ -23,7 +23,7 @@
> >      |    openrisc: | TODO |
> >      |      parisc: |  ok  |
> >      |     powerpc: |  ok  |
> > -    |       riscv: | TODO |
> > +    |       riscv: |  ok  |
> >      |        s390: |  ok  |
> >      |          sh: | TODO |
> >      |       sparc: |  ok  |
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index fd639937e251..d2f5c53fdc19 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -46,6 +46,8 @@ config RISCV
> >         select GENERIC_TIME_VSYSCALL if MMU && 64BIT
> >         select HANDLE_DOMAIN_IRQ
> >         select HAVE_ARCH_AUDITSYSCALL
> > +       select HAVE_ARCH_JUMP_LABEL
> > +       select HAVE_ARCH_JUMP_LABEL_RELATIVE
> >         select HAVE_ARCH_KASAN if MMU && 64BIT
> >         select HAVE_ARCH_KGDB
> >         select HAVE_ARCH_KGDB_QXFER_PKT
> > diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h
> > new file mode 100644
> > index 000000000000..29be6d351866
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/jump_label.h
> > @@ -0,0 +1,59 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (C) 2020 Emil Renner Berthing
> > + *
> > + * Based on arch/arm64/include/asm/jump_label.h
> > + */
> > +#ifndef __ASM_JUMP_LABEL_H
> > +#define __ASM_JUMP_LABEL_H
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <linux/types.h>
> > +
> > +#define JUMP_LABEL_NOP_SIZE 4
> > +
> > +static __always_inline bool arch_static_branch(struct static_key *key,
> > +                                              bool branch)
> > +{
> > +       asm_volatile_goto(
> > +               "       .option push                            \n\n"
> > +               "       .option norelax                         \n\n"
> > +               "       .option norvc                           \n\n"
> > +               "1:     nop                                     \n\t"
> > +               "       .option pop                             \n\n"
> > +               "       .pushsection    __jump_table, \"aw\"    \n\t"
> > +               "       .align          3                       \n\t"
> > +               "       .long           1b - ., %l[l_yes] - .   \n\t"
> > +               "       .quad           %0 - .                  \n\t"
>
> With HAVE_ARCH_JUMP_LABEL_RELATIVE we get
> struct jump_entry {
>   s32 code;
>   s32 target;
>   long key;
> }
> ..so this .quad and the one below should be replaced by the RISCV_PTR
> macro to match the struct in 32bit kernels.
>

Indeed. And nice work! Can you respin the patch with the 32b fix
above, and also without the RFC tag?

Curious; Why is [branch ? 1 : 0] needed when coding the boolean into
the key pointer (arm64 is just [branch]). Different encoding of
booleans (branch in this case)?


Cheers,
Björn

> > +               "       .popsection                             \n\t"
> > +               :  :  "i"(&((char *)key)[branch ? 1 : 0]) :  : l_yes);
> > +
> > +       return false;
> > +l_yes:
> > +       return true;
> > +}
> > +
> > +static __always_inline bool arch_static_branch_jump(struct static_key *key,
> > +                                                   bool branch)
> > +{
> > +       asm_volatile_goto(
> > +               "       .option push                            \n\n"
> > +               "       .option norelax                         \n\n"
> > +               "       .option norvc                           \n\n"
> > +               "1:     jal             zero, %l[l_yes]         \n\t"
> > +               "       .option pop                             \n\n"
> > +               "       .pushsection    __jump_table, \"aw\"    \n\t"
> > +               "       .align          3                       \n\t"
> > +               "       .long           1b - ., %l[l_yes] - .   \n\t"
> > +               "       .quad           %0 - .                  \n\t"
> > +               "       .popsection                             \n\t"
> > +               :  :  "i"(&((char *)key)[branch ? 1 : 0]) :  : l_yes);
> > +
> > +       return false;
> > +l_yes:
> > +       return true;
> > +}
> > +
> > +#endif  /* __ASSEMBLY__ */
> > +#endif /* __ASM_JUMP_LABEL_H */
> > diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> > index b355cf485671..a5287ab9f7f2 100644
> > --- a/arch/riscv/kernel/Makefile
> > +++ b/arch/riscv/kernel/Makefile
> > @@ -53,4 +53,6 @@ endif
> >  obj-$(CONFIG_HOTPLUG_CPU)      += cpu-hotplug.o
> >  obj-$(CONFIG_KGDB)             += kgdb.o
> >
> > +obj-$(CONFIG_JUMP_LABEL)       += jump_label.o
> > +
> >  clean:
> > diff --git a/arch/riscv/kernel/jump_label.c b/arch/riscv/kernel/jump_label.c
> > new file mode 100644
> > index 000000000000..55b2d742efe1
> > --- /dev/null
> > +++ b/arch/riscv/kernel/jump_label.c
> > @@ -0,0 +1,44 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Copyright (C) 2020 Emil Renner Berthing
> > + *
> > + * Based on arch/arm64/kernel/jump_label.c
> > + */
> > +#include <linux/kernel.h>
> > +#include <linux/jump_label.h>
> > +#include <asm/patch.h>
> > +
> > +#define RISCV_INSN_NOP 0x00000013
> > +#define RISCV_INSN_JAL 0x0000006f
> > +
> > +void arch_jump_label_transform(struct jump_entry *entry,
> > +                              enum jump_label_type type)
> > +{
> > +       void *addr = (void *)jump_entry_code(entry);
> > +       u32 insn;
> > +
> > +       if (type == JUMP_LABEL_JMP) {
> > +               u32 offset = jump_entry_target(entry) - jump_entry_code(entry);
> > +
> > +               insn = RISCV_INSN_JAL |
> > +                       ((offset & GENMASK(19, 12)) << (12 - 12)) |
> > +                       ((offset & GENMASK(11, 11)) << (20 - 11)) |
> > +                       ((offset & GENMASK(10,  1)) << (21 -  1)) |
> > +                       ((offset & GENMASK(20, 20)) << (31 - 20));
> > +       } else
> > +               insn = RISCV_INSN_NOP;
> > +
> > +       patch_text_nosync(addr, &insn, sizeof(insn));
> > +}
> > +
> > +void arch_jump_label_transform_static(struct jump_entry *entry,
> > +                                     enum jump_label_type type)
> > +{
> > +       /*
> > +        * We use the same instructions in the arch_static_branch and
> > +        * arch_static_branch_jump inline functions, so there's no
> > +        * need to patch them up here.
> > +        * The core will call arch_jump_label_transform  when those
> > +        * instructions need to be replaced.
> > +        */
> > +}
> > --
> > 2.27.0
> >

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