Subject: [patch V5 10/12] futex: Convert to get/put_user_inline()

From: Thomas Gleixner <[email-masked]>
Date: Mon, 27 Oct 2025 09:44:00 +0100 (CET)

From: Thomas Gleixner <[email-masked]>

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 <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
Cc: Darren Hart <[email-masked]>
Cc: Davidlohr Bueso <[email-masked]>
Cc: "André Almeida" <[email-masked]>
---
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);