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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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