linux-kernel - Re: [PATCH] uprobes: replace deprecated kmap_atomic() with kmap_local

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Message-ID: <20260205111208.GK232055@noisy.programming.kicks-ass.net>
Date: Thu, 5 Feb 2026 12:12:08 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Carlos López <clopez@...e.de>
Cc: linux-trace-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	"open list:UPROBES" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] uprobes: replace deprecated kmap_atomic() with
 kmap_local_page()

On Thu, Feb 05, 2026 at 11:57:25AM +0100, Carlos López wrote:
> kmap_atomic() has been deprecated for a few years, and kmap_local_page()
> should be used instead, so replace it. Since the uprobes code relied on
> kmap_atomic() disabling page faults to access user pages, add the
> required calls to keep the existing behavior.

Are those pagefault_disable()s really needed here, or is this just
cargo-culting?

> Signed-off-by: Carlos López <clopez@...e.de>
> ---
>  kernel/events/uprobes.c | 22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index d546d32390a8..38898435acfe 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -179,16 +179,24 @@ bool __weak is_trap_insn(uprobe_opcode_t *insn)
>  
>  void uprobe_copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len)
>  {
> -	void *kaddr = kmap_atomic(page);
> +	void *kaddr = kmap_local_page(page);
> +
> +	pagefault_disable();
>  	memcpy(dst, kaddr + (vaddr & ~PAGE_MASK), len);
> -	kunmap_atomic(kaddr);
> +	pagefault_enable();
> +
> +	kunmap_local(kaddr);
>  }
>  
>  static void copy_to_page(struct page *page, unsigned long vaddr, const void *src, int len)
>  {
> -	void *kaddr = kmap_atomic(page);
> +	void *kaddr = kmap_local_page(page);
> +
> +	pagefault_disable();
>  	memcpy(kaddr + (vaddr & ~PAGE_MASK), src, len);
> -	kunmap_atomic(kaddr);
> +	pagefault_enable();
> +
> +	kunmap_local(kaddr);
>  }
>  
>  static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *insn,
> @@ -323,9 +331,10 @@ __update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
>  		return ret == 0 ? -EBUSY : ret;
>  	}
>  
> -	kaddr = kmap_atomic(page);
> +	kaddr = kmap_local_page(page);
>  	ptr = kaddr + (vaddr & ~PAGE_MASK);
>  
> +	pagefault_disable();
>  	if (unlikely(*ptr + d < 0)) {
>  		pr_warn("ref_ctr going negative. vaddr: 0x%lx, "
>  			"curr val: %d, delta: %d\n", vaddr, *ptr, d);
> @@ -336,7 +345,8 @@ __update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
>  	*ptr += d;
>  	ret = 0;
>  out:
> -	kunmap_atomic(kaddr);
> +	pagefault_enable();
> +	kunmap_local(kaddr);
>  	put_page(page);
>  	return ret;
>  }
> 
> base-commit: f14faaf3a1fb3b9e4cf2e56269711fb85fba9458
> -- 
> 2.51.0
>