Re: [PATCH v2 1/2] openrisc: Add text patching API support

[Stafford Horne <shorne@gmail.com>]

On Wed, Aug 06, 2025 at 02:05:03AM +0000, ChenMiao wrote:
> From: chenmiao <chenmiao.ku@gmail.com>
> 
> We need a text patching mechanism to ensure that in the subsequent
> implementation of jump_label, the code can be modified to the correct
> location. Therefore, FIX_TEXT_POKE0 has been added as a mapping area.
> 
> And, I create a new file named insn-def.h to define the or1k insn macro
> size and more define in the future.
> 
> Among these changes, we implement patch_map and support the
> patch_insn_write API for single instruction writing.
> 
> - V2: We modify the patch_insn_write(void *addr, const void *insn) API to
> patch_insn_write(void *addr, u32 insn), derectly support a single u32
> instruction write to map memory.
> 
> Link: https://lore.kernel.org/openrisc/aJIC8o1WmVHol9RY@antec/T/#t
> 
> Signed-off-by: chenmiao <chenmiao.ku@gmail.com>
> ---

The v2, notes should go in this part of the patch (after ---), this way
it does not show up when I queue the patches.

>  arch/openrisc/include/asm/Kbuild          |  1 -
>  arch/openrisc/include/asm/fixmap.h        |  1 +
>  arch/openrisc/include/asm/insn-def.h      | 12 ++++
>  arch/openrisc/include/asm/text-patching.h | 13 ++++
>  arch/openrisc/kernel/Makefile             |  1 +
>  arch/openrisc/kernel/patching.c           | 79 +++++++++++++++++++++++
>  arch/openrisc/mm/init.c                   |  2 +-
>  7 files changed, 107 insertions(+), 2 deletions(-)
>  create mode 100644 arch/openrisc/include/asm/insn-def.h
>  create mode 100644 arch/openrisc/include/asm/text-patching.h
>  create mode 100644 arch/openrisc/kernel/patching.c
> 
> diff --git a/arch/openrisc/include/asm/Kbuild b/arch/openrisc/include/asm/Kbuild
> index 2b1a6b00cdac..cef49d60d74c 100644
> --- a/arch/openrisc/include/asm/Kbuild
> +++ b/arch/openrisc/include/asm/Kbuild
> @@ -9,4 +9,3 @@ generic-y += spinlock.h
>  generic-y += qrwlock_types.h
>  generic-y += qrwlock.h
>  generic-y += user.h
> -generic-y += text-patching.h
> diff --git a/arch/openrisc/include/asm/fixmap.h b/arch/openrisc/include/asm/fixmap.h
> index aaa6a26a3e92..74000215064d 100644
> --- a/arch/openrisc/include/asm/fixmap.h
> +++ b/arch/openrisc/include/asm/fixmap.h
> @@ -28,6 +28,7 @@
>  
>  enum fixed_addresses {
>  	FIX_EARLYCON_MEM_BASE,
> +	FIX_TEXT_POKE0,
>  	__end_of_fixed_addresses
>  };
>  
> diff --git a/arch/openrisc/include/asm/insn-def.h b/arch/openrisc/include/asm/insn-def.h
> new file mode 100644
> index 000000000000..dc8d16db1579
> --- /dev/null
> +++ b/arch/openrisc/include/asm/insn-def.h
> @@ -0,0 +1,12 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2025 Chen Miao
> + */
> +
> +#ifndef __ASM_INSN_DEF_H
> +#define __ASM_INSN_DEF_H
> +
> +/* or1k instructions are always 32 bits. */
> +#define	OPENRISC_INSN_SIZE		4

Is this used outside of the usage below?  Why do we need a header for it?

> +#endif /* __ASM_INSN_DEF_H */
> diff --git a/arch/openrisc/include/asm/text-patching.h b/arch/openrisc/include/asm/text-patching.h
> new file mode 100644
> index 000000000000..bffe828288c3
> --- /dev/null
> +++ b/arch/openrisc/include/asm/text-patching.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2025 Chen Miao
> + */
> +
> +#ifndef _ASM_PATCHING_H_
> +#define _ASM_PATCHING_H_
> +
> +#include <linux/types.h>
> +
> +int patch_insn_write(void *addr, u32 insn);
> +
> +#endif /* _ASM_PATCHING_H_ */
> diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
> index 58e6a1b525b7..f0957ce16d6b 100644
> --- a/arch/openrisc/kernel/Makefile
> +++ b/arch/openrisc/kernel/Makefile
> @@ -13,5 +13,6 @@ obj-$(CONFIG_SMP)		+= smp.o sync-timer.o
>  obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
>  obj-$(CONFIG_MODULES)		+= module.o
>  obj-$(CONFIG_OF)		+= prom.o
> +obj-y	+= patching.o
>  
>  clean:
> diff --git a/arch/openrisc/kernel/patching.c b/arch/openrisc/kernel/patching.c
> new file mode 100644
> index 000000000000..c9a30f0d1193
> --- /dev/null
> +++ b/arch/openrisc/kernel/patching.c
> @@ -0,0 +1,79 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (C) 2020 SiFive
> + * Copyright (C) 2025 Chen Miao
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/kernel.h>
> +#include <linux/spinlock.h>
> +#include <linux/uaccess.h>
> +
> +#include <asm/insn-def.h>
> +#include <asm/cacheflush.h>
> +#include <asm/page.h>
> +#include <asm/fixmap.h>
> +#include <asm/text-patching.h>
> +#include <asm/sections.h>
> +
> +static DEFINE_RAW_SPINLOCK(patch_lock);
> +
> +static inline bool is_exit_text(uintptr_t addr)
> +{
> +	/* Now Have NO Mechanism to do */
> +	return true;
> +}

Is this needed?  OpenRISC doesn't seem to have any sections to support __exit
annotated cleanup functions.

  Ref: https://kernelnewbies.org/FAQ/InitExitMacros

Returning true here means that all of the patch_map calls will be treated as
kernel pages below though, which is wrong, please remove this.

> +
> +static __always_inline void *patch_map(void *addr, int fixmap)
> +{
> +	uintptr_t uaddr = (uintptr_t) addr;
> +	phys_addr_t phys;
> +
> +	if (core_kernel_text(uaddr) || is_exit_text(uaddr)) {
> +		phys = __pa_symbol(addr);
> +	} else {
> +		struct page *page = vmalloc_to_page(addr);
> +		BUG_ON(!page);
> +		phys = page_to_phys(page) + offset_in_page(addr);
> +	}
> +
> +	return (void *)set_fixmap_offset(fixmap, phys);
> +}
> +
> +static void patch_unmap(int fixmap)
> +{
> +	clear_fixmap(fixmap);
> +}
> +
> +static int __patch_insn_write(void *addr, u32 insn)
> +{
> +	void *waddr = addr;
> +	unsigned long flags = 0;
> +	int ret;
> +
> +	raw_spin_lock_irqsave(&patch_lock, flags);
> +
> +	waddr = patch_map(addr, FIX_TEXT_POKE0);
> +
> +	ret = copy_to_kernel_nofault(waddr, &insn, OPENRISC_INSN_SIZE);
> +	local_icache_range_inv((unsigned long)waddr,
> +			       (unsigned long)waddr + OPENRISC_INSN_SIZE);

Instead of OPENRISC_INSN_SIZE, can you use sizeof(insn)?

> +	patch_unmap(FIX_TEXT_POKE0);
> +
> +	raw_spin_unlock_irqrestore(&patch_lock, flags);
> +
> +	return ret;
> +}
> +
> +int patch_insn_write(void *addr, u32 insn)
> +{
> +	u32 *tp = addr;
> +	int ret;
> +
> +	if ((uintptr_t) tp & 0x3)
> +		return -EINVAL;
> +
> +	ret = __patch_insn_write(tp, insn);
> +
> +	return ret;
> +}
> diff --git a/arch/openrisc/mm/init.c b/arch/openrisc/mm/init.c
> index e4904ca6f0a0..b5925710f954 100644
> --- a/arch/openrisc/mm/init.c
> +++ b/arch/openrisc/mm/init.c
> @@ -226,7 +226,7 @@ static int __init map_page(unsigned long va, phys_addr_t pa, pgprot_t prot)
>  	return 0;
>  }
>  
> -void __init __set_fixmap(enum fixed_addresses idx,
> +void __set_fixmap(enum fixed_addresses idx,

Can you put a comment about this bit in the commit description?

>  			 phys_addr_t phys, pgprot_t prot)
>  {
>  	unsigned long address = __fix_to_virt(idx);
> -- 
> 2.45.2

-Stafford