linux-kernel - [patch V5 10/12] futex: Convert to get/put_user

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Message-ID: <20251027083745.736737934@linutronix.de>
Date: Mon, 27 Oct 2025 09:44:00 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
 Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>,
 André Almeida <andrealmeid@...lia.com>,
 kernel test robot <lkp@...el.com>,
 Russell King <linux@...linux.org.uk>,
 linux-arm-kernel@...ts.infradead.org,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 x86@...nel.org,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>,
 Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 linuxppc-dev@...ts.ozlabs.org,
 Paul Walmsley <pjw@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>,
 linux-riscv@...ts.infradead.org,
 Heiko Carstens <hca@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 linux-s390@...r.kernel.org,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Cooper <andrew.cooper3@...rix.com>,
 David Laight <david.laight.linux@...il.com>,
 Julia Lawall <Julia.Lawall@...ia.fr>,
 Nicolas Palix <nicolas.palix@...g.fr>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>,
 Jan Kara <jack@...e.cz>,
 linux-fsdevel@...r.kernel.org
Subject: [patch V5 10/12] futex: Convert to get/put_user_inline()

From: Thomas Gleixner <tglx@...utronix.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@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Darren Hart <dvhart@...radead.org>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: "André Almeida" <andrealmeid@...lia.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);