From: Thomas Gleixner <tglx@linutronix.de>

Replace the open coded implementation with the new get/put_user_inline()
helpers. This might be replaced by a regular get/put_user(), but that needs
a proper performance evaluation.

No functional change intended

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "André Almeida" <andrealmeid@igalia.com>
---
V5: Rename again and remove the helpers
V4: Rename once moar
V3: Adapt to scope changes
V2: Convert to scoped variant
---
 kernel/futex/core.c  |    4 +--
 kernel/futex/futex.h |   58 ++-------------------------------------------------
 2 files changed, 5 insertions(+), 57 deletions(-)
---
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -581,7 +581,7 @@ int get_futex_key(u32 __user *uaddr, uns
 	if (flags & FLAGS_NUMA) {
 		u32 __user *naddr = (void *)uaddr + size / 2;
 
-		if (futex_get_value(&node, naddr))
+		if (get_user_inline(node, naddr))
 			return -EFAULT;
 
 		if ((node != FUTEX_NO_NODE) &&
@@ -601,7 +601,7 @@ int get_futex_key(u32 __user *uaddr, uns
 			node = numa_node_id();
 			node_updated = true;
 		}
-		if (node_updated && futex_put_value(node, naddr))
+		if (node_updated && put_user_inline(node, naddr))
 			return -EFAULT;
 	}
 
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -281,63 +281,11 @@ static inline int futex_cmpxchg_value_lo
 	return ret;
 }
 
-/*
- * This does a plain atomic user space read, and the user pointer has
- * already been verified earlier by get_futex_key() to be both aligned
- * and actually in user space, just like futex_atomic_cmpxchg_inatomic().
- *
- * We still want to avoid any speculation, and while __get_user() is
- * the traditional model for this, it's actually slower than doing
- * this manually these days.
- *
- * We could just have a per-architecture special function for it,
- * the same way we do futex_atomic_cmpxchg_inatomic(), but rather
- * than force everybody to do that, write it out long-hand using
- * the low-level user-access infrastructure.
- *
- * This looks a bit overkill, but generally just results in a couple
- * of instructions.
- */
-static __always_inline int futex_get_value(u32 *dest, u32 __user *from)
-{
-	u32 val;
-
-	if (can_do_masked_user_access())
-		from = masked_user_access_begin(from);
-	else if (!user_read_access_begin(from, sizeof(*from)))
-		return -EFAULT;
-	unsafe_get_user(val, from, Efault);
-	user_read_access_end();
-	*dest = val;
-	return 0;
-Efault:
-	user_read_access_end();
-	return -EFAULT;
-}
-
-static __always_inline int futex_put_value(u32 val, u32 __user *to)
-{
-	if (can_do_masked_user_access())
-		to = masked_user_access_begin(to);
-	else if (!user_write_access_begin(to, sizeof(*to)))
-		return -EFAULT;
-	unsafe_put_user(val, to, Efault);
-	user_write_access_end();
-	return 0;
-Efault:
-	user_write_access_end();
-	return -EFAULT;
-}
-
+/* Read from user memory with pagefaults disabled */
 static inline int futex_get_value_locked(u32 *dest, u32 __user *from)
 {
-	int ret;
-
-	pagefault_disable();
-	ret = futex_get_value(dest, from);
-	pagefault_enable();
-
-	return ret;
+	guard(pagefault)();
+	return get_user_inline(*dest, from);
 }
 
 extern void __futex_unqueue(struct futex_q *q);

Le 27/10/2025 à 09:44, Thomas Gleixner a écrit :
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> Replace the open coded implementation with the new get/put_user_inline()
> helpers. This might be replaced by a regular get/put_user(), but that needs
> a proper performance evaluation.
> 
> No functional change intended
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Darren Hart <dvhart@infradead.org>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: "André Almeida" <andrealmeid@igalia.com>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> ---
> V5: Rename again and remove the helpers
> V4: Rename once moar
> V3: Adapt to scope changes
> V2: Convert to scoped variant
> ---
>   kernel/futex/core.c  |    4 +--
>   kernel/futex/futex.h |   58 ++-------------------------------------------------
>   2 files changed, 5 insertions(+), 57 deletions(-)
> ---
> --- a/kernel/futex/core.c
> +++ b/kernel/futex/core.c
> @@ -581,7 +581,7 @@ int get_futex_key(u32 __user *uaddr, uns
>   	if (flags & FLAGS_NUMA) {
>   		u32 __user *naddr = (void *)uaddr + size / 2;
>   
> -		if (futex_get_value(&node, naddr))
> +		if (get_user_inline(node, naddr))
>   			return -EFAULT;
>   
>   		if ((node != FUTEX_NO_NODE) &&
> @@ -601,7 +601,7 @@ int get_futex_key(u32 __user *uaddr, uns
>   			node = numa_node_id();
>   			node_updated = true;
>   		}
> -		if (node_updated && futex_put_value(node, naddr))
> +		if (node_updated && put_user_inline(node, naddr))
>   			return -EFAULT;
>   	}
>   
> --- a/kernel/futex/futex.h
> +++ b/kernel/futex/futex.h
> @@ -281,63 +281,11 @@ static inline int futex_cmpxchg_value_lo
>   	return ret;
>   }
>   
> -/*
> - * This does a plain atomic user space read, and the user pointer has
> - * already been verified earlier by get_futex_key() to be both aligned
> - * and actually in user space, just like futex_atomic_cmpxchg_inatomic().
> - *
> - * We still want to avoid any speculation, and while __get_user() is
> - * the traditional model for this, it's actually slower than doing
> - * this manually these days.
> - *
> - * We could just have a per-architecture special function for it,
> - * the same way we do futex_atomic_cmpxchg_inatomic(), but rather
> - * than force everybody to do that, write it out long-hand using
> - * the low-level user-access infrastructure.
> - *
> - * This looks a bit overkill, but generally just results in a couple
> - * of instructions.
> - */
> -static __always_inline int futex_get_value(u32 *dest, u32 __user *from)
> -{
> -	u32 val;
> -
> -	if (can_do_masked_user_access())
> -		from = masked_user_access_begin(from);
> -	else if (!user_read_access_begin(from, sizeof(*from)))
> -		return -EFAULT;
> -	unsafe_get_user(val, from, Efault);
> -	user_read_access_end();
> -	*dest = val;
> -	return 0;
> -Efault:
> -	user_read_access_end();
> -	return -EFAULT;
> -}
> -
> -static __always_inline int futex_put_value(u32 val, u32 __user *to)
> -{
> -	if (can_do_masked_user_access())
> -		to = masked_user_access_begin(to);
> -	else if (!user_write_access_begin(to, sizeof(*to)))
> -		return -EFAULT;
> -	unsafe_put_user(val, to, Efault);
> -	user_write_access_end();
> -	return 0;
> -Efault:
> -	user_write_access_end();
> -	return -EFAULT;
> -}
> -
> +/* Read from user memory with pagefaults disabled */
>   static inline int futex_get_value_locked(u32 *dest, u32 __user *from)
>   {
> -	int ret;
> -
> -	pagefault_disable();
> -	ret = futex_get_value(dest, from);
> -	pagefault_enable();
> -
> -	return ret;
> +	guard(pagefault)();
> +	return get_user_inline(*dest, from);
>   }
>   
>   extern void __futex_unqueue(struct futex_q *q);
> 

On 2025-10-27 04:44, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> Replace the open coded implementation with the new get/put_user_inline()
> helpers. This might be replaced by a regular get/put_user(), but that needs
> a proper performance evaluation.

I understand that this is aiming to keep the same underlying code,
but I find it surprising that the first user of the "inline" get/put
user puts the burden of the proof on moving this to regular
get/put_user() rather than on using the inlined version.

The comment above the inline API clearly states that performance
numbers are needed to justify the use of inline, not the opposite.

I am concerned that this creates a precedent that may be used by future
users of the inline API to use it without performance numbers
justification.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

On Tue, Oct 28 2025 at 10:24, Mathieu Desnoyers wrote:
> On 2025-10-27 04:44, Thomas Gleixner wrote:
>> From: Thomas Gleixner <tglx@linutronix.de>
>> 
>> Replace the open coded implementation with the new get/put_user_inline()
>> helpers. This might be replaced by a regular get/put_user(), but that needs
>> a proper performance evaluation.
>
> I understand that this is aiming to keep the same underlying code,
> but I find it surprising that the first user of the "inline" get/put
> user puts the burden of the proof on moving this to regular
> get/put_user() rather than on using the inlined version.
>
> The comment above the inline API clearly states that performance
> numbers are needed to justify the use of inline, not the opposite.
>
> I am concerned that this creates a precedent that may be used by future
> users of the inline API to use it without performance numbers
> justification.

There was not justification for the open coded inline either and
converting it to get/put must be a completely seperate change.

On Tue, 28 Oct 2025 at 08:56, Thomas Gleixner <tglx@linutronix.de> wrote:
>
> There was not justification for the open coded inline either and
> converting it to get/put must be a completely seperate change.

Actually, there's some justification in the original: see commit
43a43faf5376 ("futex: improve user space accesses") which talks about
the original impetus for it all: avoiding the very expensive barrier
in __get_user(), and how __get_user() itself couldn't be fixed.

So then it was converted to the modern user access helpers - including
address masking - and the inlining was mostly incidental to that, but
the commit message does point out that it actually makes the address
generation a bit cleaner in addition to avoiding the function call.

But I doubt that the extra instructions are all that noticeable.

That said - this code *is* in a very hot path on some loads, so it is
entirely possible that the inlining here is noticeable. I$ patterns in
particular can be a real thing.

(There was an additional issue of just making those user accesses -
get, put and cmpxchg - look a bit more similar)

           Linus

On 2025-10-28 11:56, Thomas Gleixner wrote:
> On Tue, Oct 28 2025 at 10:24, Mathieu Desnoyers wrote:
>> On 2025-10-27 04:44, Thomas Gleixner wrote:
>>> From: Thomas Gleixner <tglx@linutronix.de>
>>>
>>> Replace the open coded implementation with the new get/put_user_inline()
>>> helpers. This might be replaced by a regular get/put_user(), but that needs
>>> a proper performance evaluation.
>>
>> I understand that this is aiming to keep the same underlying code,
>> but I find it surprising that the first user of the "inline" get/put
>> user puts the burden of the proof on moving this to regular
>> get/put_user() rather than on using the inlined version.
>>
>> The comment above the inline API clearly states that performance
>> numbers are needed to justify the use of inline, not the opposite.
>>
>> I am concerned that this creates a precedent that may be used by future
>> users of the inline API to use it without performance numbers
>> justification.
> 
> There was not justification for the open coded inline either and
> converting it to get/put must be a completely seperate change.

AFAIU there was justification from Linus in
commit 43a43faf5376 ("futex: improve user space accesses").

Perhaps it's good enough to refer to that prior justification
in the commit message.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

The following commit has been merged into the core/rseq branch of tip:

Commit-ID:     e4e28fd6986e8cf963ec4137e6c0b95403f636ab
Gitweb:        https://git.kernel.org/tip/e4e28fd6986e8cf963ec4137e6c0b95403f636ab
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Mon, 27 Oct 2025 09:44:00 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 04 Nov 2025 08:28:23 +01:00

futex: Convert to get/put_user_inline()

Replace the open coded implementation with the new get/put_user_inline()
helpers. This might be replaced by a regular get/put_user(), but that needs
a proper performance evaluation.

No functional change intended.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251027083745.736737934@linutronix.de
---
 kernel/futex/core.c  |  4 +--
 kernel/futex/futex.h | 58 ++-----------------------------------------
 2 files changed, 5 insertions(+), 57 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 125804f..ebcccb1 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -581,7 +581,7 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
 	if (flags & FLAGS_NUMA) {
 		u32 __user *naddr = (void *)uaddr + size / 2;
 
-		if (futex_get_value(&node, naddr))
+		if (get_user_inline(node, naddr))
 			return -EFAULT;
 
 		if ((node != FUTEX_NO_NODE) &&
@@ -601,7 +601,7 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
 			node = numa_node_id();
 			node_updated = true;
 		}
-		if (node_updated && futex_put_value(node, naddr))
+		if (node_updated && put_user_inline(node, naddr))
 			return -EFAULT;
 	}
 
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 2cd5709..30c2afa 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -281,63 +281,11 @@ static inline int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr, u32
 	return ret;
 }
 
-/*
- * This does a plain atomic user space read, and the user pointer has
- * already been verified earlier by get_futex_key() to be both aligned
- * and actually in user space, just like futex_atomic_cmpxchg_inatomic().
- *
- * We still want to avoid any speculation, and while __get_user() is
- * the traditional model for this, it's actually slower than doing
- * this manually these days.
- *
- * We could just have a per-architecture special function for it,
- * the same way we do futex_atomic_cmpxchg_inatomic(), but rather
- * than force everybody to do that, write it out long-hand using
- * the low-level user-access infrastructure.
- *
- * This looks a bit overkill, but generally just results in a couple
- * of instructions.
- */
-static __always_inline int futex_get_value(u32 *dest, u32 __user *from)
-{
-	u32 val;
-
-	if (can_do_masked_user_access())
-		from = masked_user_access_begin(from);
-	else if (!user_read_access_begin(from, sizeof(*from)))
-		return -EFAULT;
-	unsafe_get_user(val, from, Efault);
-	user_read_access_end();
-	*dest = val;
-	return 0;
-Efault:
-	user_read_access_end();
-	return -EFAULT;
-}
-
-static __always_inline int futex_put_value(u32 val, u32 __user *to)
-{
-	if (can_do_masked_user_access())
-		to = masked_user_access_begin(to);
-	else if (!user_write_access_begin(to, sizeof(*to)))
-		return -EFAULT;
-	unsafe_put_user(val, to, Efault);
-	user_write_access_end();
-	return 0;
-Efault:
-	user_write_access_end();
-	return -EFAULT;
-}
-
+/* Read from user memory with pagefaults disabled */
 static inline int futex_get_value_locked(u32 *dest, u32 __user *from)
 {
-	int ret;
-
-	pagefault_disable();
-	ret = futex_get_value(dest, from);
-	pagefault_enable();
-
-	return ret;
+	guard(pagefault)();
+	return get_user_inline(*dest, from);
 }
 
 extern void __futex_unqueue(struct futex_q *q);

The following commit has been merged into the core/rseq branch of tip:

Commit-ID:     103ee619d2955cbddab3d13c87113aa9a42601c5
Gitweb:        https://git.kernel.org/tip/103ee619d2955cbddab3d13c87113aa9a42601c5
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Mon, 27 Oct 2025 09:44:00 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 03 Nov 2025 15:26:11 +01:00

futex: Convert to get/put_user_inline()

Replace the open coded implementation with the new get/put_user_inline()
helpers. This might be replaced by a regular get/put_user(), but that needs
a proper performance evaluation.

No functional change intended

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251027083745.736737934@linutronix.de
---
 kernel/futex/core.c  |  4 +--
 kernel/futex/futex.h | 58 ++-----------------------------------------
 2 files changed, 5 insertions(+), 57 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 125804f..ebcccb1 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -581,7 +581,7 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
 	if (flags & FLAGS_NUMA) {
 		u32 __user *naddr = (void *)uaddr + size / 2;
 
-		if (futex_get_value(&node, naddr))
+		if (get_user_inline(node, naddr))
 			return -EFAULT;
 
 		if ((node != FUTEX_NO_NODE) &&
@@ -601,7 +601,7 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
 			node = numa_node_id();
 			node_updated = true;
 		}
-		if (node_updated && futex_put_value(node, naddr))
+		if (node_updated && put_user_inline(node, naddr))
 			return -EFAULT;
 	}
 
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 2cd5709..30c2afa 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -281,63 +281,11 @@ static inline int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr, u32
 	return ret;
 }
 
-/*
- * This does a plain atomic user space read, and the user pointer has
- * already been verified earlier by get_futex_key() to be both aligned
- * and actually in user space, just like futex_atomic_cmpxchg_inatomic().
- *
- * We still want to avoid any speculation, and while __get_user() is
- * the traditional model for this, it's actually slower than doing
- * this manually these days.
- *
- * We could just have a per-architecture special function for it,
- * the same way we do futex_atomic_cmpxchg_inatomic(), but rather
- * than force everybody to do that, write it out long-hand using
- * the low-level user-access infrastructure.
- *
- * This looks a bit overkill, but generally just results in a couple
- * of instructions.
- */
-static __always_inline int futex_get_value(u32 *dest, u32 __user *from)
-{
-	u32 val;
-
-	if (can_do_masked_user_access())
-		from = masked_user_access_begin(from);
-	else if (!user_read_access_begin(from, sizeof(*from)))
-		return -EFAULT;
-	unsafe_get_user(val, from, Efault);
-	user_read_access_end();
-	*dest = val;
-	return 0;
-Efault:
-	user_read_access_end();
-	return -EFAULT;
-}
-
-static __always_inline int futex_put_value(u32 val, u32 __user *to)
-{
-	if (can_do_masked_user_access())
-		to = masked_user_access_begin(to);
-	else if (!user_write_access_begin(to, sizeof(*to)))
-		return -EFAULT;
-	unsafe_put_user(val, to, Efault);
-	user_write_access_end();
-	return 0;
-Efault:
-	user_write_access_end();
-	return -EFAULT;
-}
-
+/* Read from user memory with pagefaults disabled */
 static inline int futex_get_value_locked(u32 *dest, u32 __user *from)
 {
-	int ret;
-
-	pagefault_disable();
-	ret = futex_get_value(dest, from);
-	pagefault_enable();
-
-	return ret;
+	guard(pagefault)();
+	return get_user_inline(*dest, from);
 }
 
 extern void __futex_unqueue(struct futex_q *q);

The following commit has been merged into the core/rseq branch of tip:

Commit-ID:     536e6a70108b609e36866efe8c401d1ed32759ea
Gitweb:        https://git.kernel.org/tip/536e6a70108b609e36866efe8c401d1ed32759ea
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Mon, 27 Oct 2025 09:44:00 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 29 Oct 2025 11:07:10 +01:00

futex: Convert to get/put_user_inline()

Replace the open coded implementation with the new get/put_user_inline()
helpers. This might be replaced by a regular get/put_user(), but that needs
a proper performance evaluation.

No functional change intended

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251027083745.736737934@linutronix.de
---
 kernel/futex/core.c  |  4 +--
 kernel/futex/futex.h | 58 ++-----------------------------------------
 2 files changed, 5 insertions(+), 57 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 125804f..ebcccb1 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -581,7 +581,7 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
 	if (flags & FLAGS_NUMA) {
 		u32 __user *naddr = (void *)uaddr + size / 2;
 
-		if (futex_get_value(&node, naddr))
+		if (get_user_inline(node, naddr))
 			return -EFAULT;
 
 		if ((node != FUTEX_NO_NODE) &&
@@ -601,7 +601,7 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
 			node = numa_node_id();
 			node_updated = true;
 		}
-		if (node_updated && futex_put_value(node, naddr))
+		if (node_updated && put_user_inline(node, naddr))
 			return -EFAULT;
 	}
 
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 2cd5709..30c2afa 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -281,63 +281,11 @@ static inline int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr, u32
 	return ret;
 }
 
-/*
- * This does a plain atomic user space read, and the user pointer has
- * already been verified earlier by get_futex_key() to be both aligned
- * and actually in user space, just like futex_atomic_cmpxchg_inatomic().
- *
- * We still want to avoid any speculation, and while __get_user() is
- * the traditional model for this, it's actually slower than doing
- * this manually these days.
- *
- * We could just have a per-architecture special function for it,
- * the same way we do futex_atomic_cmpxchg_inatomic(), but rather
- * than force everybody to do that, write it out long-hand using
- * the low-level user-access infrastructure.
- *
- * This looks a bit overkill, but generally just results in a couple
- * of instructions.
- */
-static __always_inline int futex_get_value(u32 *dest, u32 __user *from)
-{
-	u32 val;
-
-	if (can_do_masked_user_access())
-		from = masked_user_access_begin(from);
-	else if (!user_read_access_begin(from, sizeof(*from)))
-		return -EFAULT;
-	unsafe_get_user(val, from, Efault);
-	user_read_access_end();
-	*dest = val;
-	return 0;
-Efault:
-	user_read_access_end();
-	return -EFAULT;
-}
-
-static __always_inline int futex_put_value(u32 val, u32 __user *to)
-{
-	if (can_do_masked_user_access())
-		to = masked_user_access_begin(to);
-	else if (!user_write_access_begin(to, sizeof(*to)))
-		return -EFAULT;
-	unsafe_put_user(val, to, Efault);
-	user_write_access_end();
-	return 0;
-Efault:
-	user_write_access_end();
-	return -EFAULT;
-}
-
+/* Read from user memory with pagefaults disabled */
 static inline int futex_get_value_locked(u32 *dest, u32 __user *from)
 {
-	int ret;
-
-	pagefault_disable();
-	ret = futex_get_value(dest, from);
-	pagefault_enable();
-
-	return ret;
+	guard(pagefault)();
+	return get_user_inline(*dest, from);
 }
 
 extern void __futex_unqueue(struct futex_q *q);