Re: [PATCH v2 1/4] sparc64: kprobes: Single-step from an executable instruction slot

[Masami Hiramatsu (Google)]

On Fri, 13 Nov 2026 15:40:54 +0100, Stian Halseth <stian@xxxxxx> wrote:
> kprobes single-steps the probed instruction from kprobe->ainsn.insn[].
> The array is embedded in struct kprobe, in the linear mapping. The
> sun4v linear mapping is not executable. Every probe hit oopses:
> 
>   sun4v_insn_access_exception: ADDR[fff800005b0cd66c] CTX[0000] TYPE[0006], going.
> 
> Allocate the copy with get_insn_slot(), as other architectures do. The
> slot comes from executable memory in the module area.
> 
> flush_insn_slot() flushed the embedded copy after init_aggr_kprobe()
> had copied it into the aggregator. The aggregator now shares the slot
> by pointer. arch_prepare_kprobe() flushes the slot when it writes it.
> Make the macro a no-op, like x86 and arm64.
> 
> Fixes: c4bce90ea2069 ("[SPARC64]: Deal with PTE layout differences in SUN4V.")
> Closes: https://github.com/sparclinux/issues/issues/110
> Signed-off-by: Stian Halseth <stian@xxxxxx>

Looks good to me from kprobe point of view.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Thanks,

> ---
>  arch/sparc/include/asm/kprobes.h | 12 ++++++------
>  arch/sparc/kernel/kprobes.c      | 12 ++++++++++++
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/sparc/include/asm/kprobes.h b/arch/sparc/include/asm/kprobes.h
> index aec742cd898f2..d14206c063e25 100644
> --- a/arch/sparc/include/asm/kprobes.h
> +++ b/arch/sparc/include/asm/kprobes.h
> @@ -11,25 +11,25 @@
>  #include <linux/types.h>
>  #include <linux/percpu.h>
>  
> +#define __ARCH_WANT_KPROBES_INSN_SLOT
> +
>  typedef u32 kprobe_opcode_t;
>  
>  #define MAX_INSN_SIZE 2
>  
>  #define kretprobe_blacklist_size 0
>  
> -#define arch_remove_kprobe(p)	do {} while (0)
> +struct kprobe;
> +void arch_remove_kprobe(struct kprobe *p);
>  
> -#define flush_insn_slot(p)		\
> -do { 	flushi(&(p)->ainsn.insn[0]);	\
> -	flushi(&(p)->ainsn.insn[1]);	\
> -} while (0)
> +#define flush_insn_slot(p)	do { } while (0)
>  
>  void __kretprobe_trampoline(void);
>  
>  /* Architecture specific copy of original instruction*/
>  struct arch_specific_insn {
>  	/* copy of the original instruction */
> -	kprobe_opcode_t insn[MAX_INSN_SIZE];
> +	kprobe_opcode_t *insn;
>  };
>  
>  struct prev_kprobe {
> diff --git a/arch/sparc/kernel/kprobes.c b/arch/sparc/kernel/kprobes.c
> index 191bbaca99212..608efda8cb948 100644
> --- a/arch/sparc/kernel/kprobes.c
> +++ b/arch/sparc/kernel/kprobes.c
> @@ -52,6 +52,10 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  	if ((unsigned long) p->addr & 0x3UL)
>  		return -EILSEQ;
>  
> +	p->ainsn.insn = get_insn_slot();
> +	if (!p->ainsn.insn)
> +		return -ENOMEM;
> +
>  	p->ainsn.insn[0] = *p->addr;
>  	flushi(&p->ainsn.insn[0]);
>  
> @@ -62,6 +66,14 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  	return 0;
>  }
>  
> +void __kprobes arch_remove_kprobe(struct kprobe *p)
> +{
> +	if (p->ainsn.insn) {
> +		free_insn_slot(p->ainsn.insn, 0);
> +		p->ainsn.insn = NULL;
> +	}
> +}
> +
>  void __kprobes arch_arm_kprobe(struct kprobe *p)
>  {
>  	*p->addr = BREAKPOINT_INSTRUCTION;
> -- 
> 2.43.0
> 
>

-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>