linux-kernel - Re: [PATCH RFCv2 06/18] uprobes: Add orig argument to uprobe_write and uprobe_write

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Message-ID: <CAEf4BzZ=TOGXMwYDz1=bdw4DVVgkXJkMKKv=O1HnWddS-i6Kww@mail.gmail.com>
Date: Fri, 28 Feb 2025 11:07:38 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, x86@...nel.org, 
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, Hao Luo <haoluo@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Alan Maguire <alan.maguire@...cle.com>, David Laight <David.Laight@...lab.com>, 
	Thomas Weißschuh <thomas@...ch.de>
Subject: Re: [PATCH RFCv2 06/18] uprobes: Add orig argument to uprobe_write
 and uprobe_write_opcode

On Mon, Feb 24, 2025 at 6:03 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> The uprobe_write has special path to restore the original page when
> we write original instruction back.
>
> This happens when uprobe_write detects that we want to write anything
> else but breakpoint instruction.
>
> In following changes we want to use uprobe_write function for multiple
> updates, so adding new function argument to denote that this is the
> original instruction update. This way uprobe_write can make appropriate
> checks and restore the original page when possible.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  arch/arm/probes/uprobes/core.c |  2 +-
>  include/linux/uprobes.h        |  5 +++--
>  kernel/events/uprobes.c        | 22 ++++++++++------------
>  3 files changed, 14 insertions(+), 15 deletions(-)
>

[...]

> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index ad5879fc2d26..2b542043089e 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -471,25 +471,23 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
>   * Return 0 (success) or a negative errno.
>   */
>  int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> -                       unsigned long vaddr, uprobe_opcode_t opcode)
> +                       unsigned long vaddr, uprobe_opcode_t opcode, bool orig)
>  {
> -       return uprobe_write(auprobe, mm, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE, verify_opcode);
> +       return uprobe_write(auprobe, mm, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE, verify_opcode, orig);
>  }
>
>  int uprobe_write(struct arch_uprobe *auprobe, struct mm_struct *mm,
>                  unsigned long vaddr, uprobe_opcode_t *insn,
> -                int nbytes, uprobe_write_verify_t verify)
> +                int nbytes, uprobe_write_verify_t verify, bool orig)

why not call orig -> is_register and avoid a bunch of code churn?...
(and while "is_register" is not awesome name, still a bit more clear
compared to "orig", IMO)

>  {
>         struct page *old_page, *new_page;
>         struct vm_area_struct *vma;
> -       int ret, is_register;
> +       int ret;
>         bool orig_page_huge = false;
>         unsigned int gup_flags = FOLL_FORCE;
>
> -       is_register = is_swbp_insn(insn);
> -

[...]