Re: [PATCH] riscv: patch: Remove redundant functions

[Samuel Holland <samuel.holland@sifive.com>]

Hi Alex,

On 2024-07-17 3:41 AM, Alexandre Ghiti wrote:
> Commit edf2d546bfd6f5c4 ("riscv: patch: Flush the icache right after
> patching to avoid illegal insns") removed the last differences between
> patch_text_set_nosync() and patch_insn_set(), and between
> patch_text_nosync() and patch_insn_write().
> 
> So remove the redundant *_nosync() functions.

My understanding was that we would eventually revert that patch, once we are
sure we never non-atomically patch the text patching code. So it's helpful to
keep the semantic distinction between the two sets of functions.

And looking at this closer, I think the original patch should not have removed
the calls to flush_icache_range() anyway. It replaces a global icache flush with
a local icache flush, which is wrong if there is more than one CPU online, and
there are a couple of places (bpf_jit_core.c, kprobes.c) where those functions
are called at runtime.

Regards,
Samuel

> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Closes: https://lore.kernel.org/linux-riscv/CAMuHMdUwx=rU2MWhFTE6KhYHm64phxx2Y6u05-aBLGfeG5696A@mail.gmail.com/
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  arch/riscv/errata/sifive/errata.c |  4 ++--
>  arch/riscv/errata/thead/errata.c  |  2 +-
>  arch/riscv/include/asm/patch.h    |  3 +--
>  arch/riscv/kernel/alternative.c   |  4 ++--
>  arch/riscv/kernel/cpufeature.c    |  2 +-
>  arch/riscv/kernel/jump_label.c    |  2 +-
>  arch/riscv/kernel/patch.c         | 24 +-----------------------
>  arch/riscv/net/bpf_jit_core.c     |  4 ++--
>  8 files changed, 11 insertions(+), 34 deletions(-)
> 
> diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
> index 716cfedad3a2..5253b205aa17 100644
> --- a/arch/riscv/errata/sifive/errata.c
> +++ b/arch/riscv/errata/sifive/errata.c
> @@ -112,8 +112,8 @@ void sifive_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  		tmp = (1U << alt->patch_id);
>  		if (cpu_req_errata & tmp) {
>  			mutex_lock(&text_mutex);
> -			patch_text_nosync(ALT_OLD_PTR(alt), ALT_ALT_PTR(alt),
> -					  alt->alt_len);
> +			patch_insn_write(ALT_OLD_PTR(alt), ALT_ALT_PTR(alt),
> +					 alt->alt_len);
>  			mutex_unlock(&text_mutex);
>  			cpu_apply_errata |= tmp;
>  		}
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index bf6a0a6318ee..0ce280a190b6 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -182,7 +182,7 @@ void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  				memcpy(oldptr, altptr, alt->alt_len);
>  			} else {
>  				mutex_lock(&text_mutex);
> -				patch_text_nosync(oldptr, altptr, alt->alt_len);
> +				patch_insn_write(oldptr, altptr, alt->alt_len);
>  				mutex_unlock(&text_mutex);
>  			}
>  		}
> diff --git a/arch/riscv/include/asm/patch.h b/arch/riscv/include/asm/patch.h
> index 9f5d6e14c405..6b0e9b8a321b 100644
> --- a/arch/riscv/include/asm/patch.h
> +++ b/arch/riscv/include/asm/patch.h
> @@ -6,9 +6,8 @@
>  #ifndef _ASM_RISCV_PATCH_H
>  #define _ASM_RISCV_PATCH_H
>  
> +int patch_insn_set(void *addr, u8 c, size_t len);
>  int patch_insn_write(void *addr, const void *insn, size_t len);
> -int patch_text_nosync(void *addr, const void *insns, size_t len);
> -int patch_text_set_nosync(void *addr, u8 c, size_t len);
>  int patch_text(void *addr, u32 *insns, int ninsns);
>  
>  extern int riscv_patch_in_stop_machine;
> diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
> index 0128b161bfda..a8b508d99cf8 100644
> --- a/arch/riscv/kernel/alternative.c
> +++ b/arch/riscv/kernel/alternative.c
> @@ -83,7 +83,7 @@ static void riscv_alternative_fix_auipc_jalr(void *ptr, u32 auipc_insn,
>  	riscv_insn_insert_utype_itype_imm(&call[0], &call[1], imm);
>  
>  	/* patch the call place again */
> -	patch_text_nosync(ptr, call, sizeof(u32) * 2);
> +	patch_insn_write(ptr, call, sizeof(u32) * 2);
>  }
>  
>  static void riscv_alternative_fix_jal(void *ptr, u32 jal_insn, int patch_offset)
> @@ -98,7 +98,7 @@ static void riscv_alternative_fix_jal(void *ptr, u32 jal_insn, int patch_offset)
>  	riscv_insn_insert_jtype_imm(&jal_insn, imm);
>  
>  	/* patch the call place again */
> -	patch_text_nosync(ptr, &jal_insn, sizeof(u32));
> +	patch_insn_write(ptr, &jal_insn, sizeof(u32));
>  }
>  
>  void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 5ef48cb20ee1..4c040a857c7e 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -795,7 +795,7 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
>  		altptr = ALT_ALT_PTR(alt);
>  
>  		mutex_lock(&text_mutex);
> -		patch_text_nosync(oldptr, altptr, alt->alt_len);
> +		patch_insn_write(oldptr, altptr, alt->alt_len);
>  		riscv_alternative_fix_offsets(oldptr, alt->alt_len, oldptr - altptr);
>  		mutex_unlock(&text_mutex);
>  	}
> diff --git a/arch/riscv/kernel/jump_label.c b/arch/riscv/kernel/jump_label.c
> index e6694759dbd0..74b5ebfacf4a 100644
> --- a/arch/riscv/kernel/jump_label.c
> +++ b/arch/riscv/kernel/jump_label.c
> @@ -36,6 +36,6 @@ void arch_jump_label_transform(struct jump_entry *entry,
>  	}
>  
>  	mutex_lock(&text_mutex);
> -	patch_text_nosync(addr, &insn, sizeof(insn));
> +	patch_insn_write(addr, &insn, sizeof(insn));
>  	mutex_unlock(&text_mutex);
>  }
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index ab03732d06c4..bf45b507f900 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -177,7 +177,7 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
>  NOKPROBE_SYMBOL(__patch_insn_write);
>  #endif /* CONFIG_MMU */
>  
> -static int patch_insn_set(void *addr, u8 c, size_t len)
> +int patch_insn_set(void *addr, u8 c, size_t len)
>  {
>  	size_t patched = 0;
>  	size_t size;
> @@ -198,17 +198,6 @@ static int patch_insn_set(void *addr, u8 c, size_t len)
>  }
>  NOKPROBE_SYMBOL(patch_insn_set);
>  
> -int patch_text_set_nosync(void *addr, u8 c, size_t len)
> -{
> -	u32 *tp = addr;
> -	int ret;
> -
> -	ret = patch_insn_set(tp, c, len);
> -
> -	return ret;
> -}
> -NOKPROBE_SYMBOL(patch_text_set_nosync);
> -
>  int patch_insn_write(void *addr, const void *insn, size_t len)
>  {
>  	size_t patched = 0;
> @@ -230,17 +219,6 @@ int patch_insn_write(void *addr, const void *insn, size_t len)
>  }
>  NOKPROBE_SYMBOL(patch_insn_write);
>  
> -int patch_text_nosync(void *addr, const void *insns, size_t len)
> -{
> -	u32 *tp = addr;
> -	int ret;
> -
> -	ret = patch_insn_write(tp, insns, len);
> -
> -	return ret;
> -}
> -NOKPROBE_SYMBOL(patch_text_nosync);
> -
>  static int patch_text_cb(void *data)
>  {
>  	struct patch_insn *patch = data;
> diff --git a/arch/riscv/net/bpf_jit_core.c b/arch/riscv/net/bpf_jit_core.c
> index 0a96abdaca65..b053ae5c4191 100644
> --- a/arch/riscv/net/bpf_jit_core.c
> +++ b/arch/riscv/net/bpf_jit_core.c
> @@ -226,7 +226,7 @@ void *bpf_arch_text_copy(void *dst, void *src, size_t len)
>  	int ret;
>  
>  	mutex_lock(&text_mutex);
> -	ret = patch_text_nosync(dst, src, len);
> +	ret = patch_insn_write(dst, src, len);
>  	mutex_unlock(&text_mutex);
>  
>  	if (ret)
> @@ -240,7 +240,7 @@ int bpf_arch_text_invalidate(void *dst, size_t len)
>  	int ret;
>  
>  	mutex_lock(&text_mutex);
> -	ret = patch_text_set_nosync(dst, 0, len);
> +	ret = patch_insn_set(dst, 0, len);
>  	mutex_unlock(&text_mutex);
>  
>  	return ret;