uprobes: replace deprecated kmap_atomic() with kmap_local_page()

[PATCH] uprobes: replace deprecated kmap_atomic() with kmap_local_page()

Posted by Carlos López 1 day, 20 hours ago

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.

Signed-off-by: Carlos López <clopez@suse.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

Re: [PATCH] uprobes: replace deprecated kmap_atomic() with kmap_local_page()

Posted by Oleg Nesterov 1 day, 20 hours ago

Hi Carlos,

see

	[PATCH 0/5] uprobes: transition from kmap_atomic to kmap_local_page
	https://lore.kernel.org/all/20260103084243.195125-1-ming.jvle@gmail.com/

already in tip/perf/core

Oleg.

On 02/05, 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.
>
> Signed-off-by: Carlos López <clopez@suse.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
>

Re: [PATCH] uprobes: replace deprecated kmap_atomic() with kmap_local_page()

Posted by Carlos López 1 day, 20 hours ago

On 2/5/26 12:25 PM, Oleg Nesterov wrote:
> Hi Carlos,
> 
> see
> 
> 	[PATCH 0/5] uprobes: transition from kmap_atomic to kmap_local_page
> 	https://lore.kernel.org/all/20260103084243.195125-1-ming.jvle@gmail.com/
> 
> already in tip/perf/core

Ah, looks like I was looking at the wrong tree, sorry for the noise.

Re: [PATCH] uprobes: replace deprecated kmap_atomic() with kmap_local_page()

Posted by Peter Zijlstra 1 day, 20 hours ago

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@suse.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
>

Re: [PATCH] uprobes: replace deprecated kmap_atomic() with kmap_local_page()

Posted by Oleg Nesterov 1 day, 19 hours ago

On 02/05, Peter Zijlstra wrote:
>
> 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?

No, I think there are not needed.

And the (already in tip) patches from Keke do not add pagefault_disable().

is_trap_at_addr() does pagefault_disable() because it is called with
mm->mmap_lock held.

Oleg.

Re: [PATCH] uprobes: replace deprecated kmap_atomic() with kmap_local_page()

Posted by Carlos López 1 day, 20 hours ago

Hi,

On 2/5/26 12:12 PM, Peter Zijlstra wrote:
> 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?

The subsystem experts can correct me, but it seems to me this code is
primarily accessing user memory, e.g. is_trap_at_addr() ->
get_user_pages() -> uprobe_copy_from_page().