uaccess: unify inline vs outline copy_{from,to}_user() selection

[PATCH 1/2] uaccess: unify inline vs outline copy_{from,to}_user() selection

Posted by Yury Norov 1 week, 1 day ago

The kernel allows arches to select between inline and outline
implementations of the copy_{from,to}_user() by defining individual
INLINE_COPY_FROM_USER and INLINE_COPY_TO_USER, correspondingly.
However, all arches enable or disable them always together.

Without the real use-case for one helper being inlined while the other
outlined, having independent controls is excessive and error prone.

Switch the codebase to the single unified INLINE_COPY_USER control.

Reported-by: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
Closes: https://lore.kernel.org/all/746c9c50-20c4-4dc9-a539-bf1310ff9414@kernel.org/
Fixes: 1f9a8286bc0c ("uaccess: always export _copy_[from|to]_user with CONFIG_RUST")
Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
 arch/arc/include/asm/uaccess.h        |  3 +--
 arch/arm/include/asm/uaccess.h        |  3 +--
 arch/arm64/include/asm/uaccess.h      |  3 +--
 arch/hexagon/include/asm/uaccess.h    |  3 +--
 arch/loongarch/include/asm/uaccess.h  |  3 +--
 arch/m68k/include/asm/uaccess.h       |  3 +--
 arch/microblaze/include/asm/uaccess.h |  3 +--
 arch/mips/include/asm/uaccess.h       |  3 +--
 arch/nios2/include/asm/uaccess.h      |  3 +--
 arch/openrisc/include/asm/uaccess.h   |  3 +--
 arch/parisc/include/asm/uaccess.h     |  3 +--
 arch/s390/include/asm/uaccess.h       |  3 +--
 arch/sh/include/asm/uaccess.h         |  3 +--
 arch/sparc/include/asm/uaccess_32.h   |  3 +--
 arch/sparc/include/asm/uaccess_64.h   |  3 +--
 arch/um/include/asm/uaccess.h         |  3 +--
 arch/xtensa/include/asm/uaccess.h     |  3 +--
 include/asm-generic/uaccess.h         |  3 +--
 include/linux/uaccess.h               | 12 ++++++------
 lib/usercopy.c                        |  4 +---
 rust/helpers/uaccess.c                |  2 +-
 21 files changed, 26 insertions(+), 46 deletions(-)

diff --git a/arch/arc/include/asm/uaccess.h b/arch/arc/include/asm/uaccess.h
index 1e8809ea000a..6df2209541ac 100644
--- a/arch/arc/include/asm/uaccess.h
+++ b/arch/arc/include/asm/uaccess.h
@@ -628,8 +628,7 @@ static inline unsigned long __clear_user(void __user *to, unsigned long n)
 	return res;
 }
 
-#define INLINE_COPY_TO_USER
-#define INLINE_COPY_FROM_USER
+#define INLINE_COPY_USER
 
 #define __clear_user			__clear_user
 
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index d6ae80b5df36..1593cf3b9800 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -616,8 +616,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 }
 #define __clear_user(addr, n)		(memset((void __force *)addr, 0, n), 0)
 #endif
-#define INLINE_COPY_TO_USER
-#define INLINE_COPY_FROM_USER
+#define INLINE_COPY_USER
 
 static inline unsigned long __must_check clear_user(void __user *to, unsigned long n)
 {
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 9810106a3f66..d8be8cb45050 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -456,8 +456,7 @@ do {									\
 	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
 } while (0)
 
-#define INLINE_COPY_TO_USER
-#define INLINE_COPY_FROM_USER
+#define INLINE_COPY_USER
 
 extern unsigned long __must_check __arch_clear_user(void __user *to, unsigned long n);
 static inline unsigned long __must_check __clear_user(void __user *to, unsigned long n)
diff --git a/arch/hexagon/include/asm/uaccess.h b/arch/hexagon/include/asm/uaccess.h
index bff77efc0d9a..1aecf60ec4f5 100644
--- a/arch/hexagon/include/asm/uaccess.h
+++ b/arch/hexagon/include/asm/uaccess.h
@@ -26,8 +26,7 @@ unsigned long raw_copy_from_user(void *to, const void __user *from,
 				     unsigned long n);
 unsigned long raw_copy_to_user(void __user *to, const void *from,
 				   unsigned long n);
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 __kernel_size_t __clear_user_hexagon(void __user *dest, unsigned long count);
 #define __clear_user(a, s) __clear_user_hexagon((a), (s))
diff --git a/arch/loongarch/include/asm/uaccess.h b/arch/loongarch/include/asm/uaccess.h
index 438269313e78..428f373feabf 100644
--- a/arch/loongarch/include/asm/uaccess.h
+++ b/arch/loongarch/include/asm/uaccess.h
@@ -292,8 +292,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 	return __copy_user((__force void *)to, from, n);
 }
 
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 /*
  * __clear_user: - Zero a block of memory in user space, with less checking.
diff --git a/arch/m68k/include/asm/uaccess.h b/arch/m68k/include/asm/uaccess.h
index 64914872a5c9..31d133faa45e 100644
--- a/arch/m68k/include/asm/uaccess.h
+++ b/arch/m68k/include/asm/uaccess.h
@@ -377,8 +377,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 		return __constant_copy_to_user(to, from, n);
 	return __generic_copy_to_user(to, from, n);
 }
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 #define __get_kernel_nofault(dst, src, type, err_label)			\
 do {									\
diff --git a/arch/microblaze/include/asm/uaccess.h b/arch/microblaze/include/asm/uaccess.h
index 3aab2f17e046..afa0dd8d013f 100644
--- a/arch/microblaze/include/asm/uaccess.h
+++ b/arch/microblaze/include/asm/uaccess.h
@@ -250,8 +250,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	return __copy_tofrom_user(to, (__force const void __user *)from, n);
 }
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 /*
  * Copy a null terminated string from userspace.
diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
index c0cede273c7c..f00c36676b73 100644
--- a/arch/mips/include/asm/uaccess.h
+++ b/arch/mips/include/asm/uaccess.h
@@ -433,8 +433,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 	return __cu_len_r;
 }
 
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 extern __kernel_size_t __bzero(void __user *addr, __kernel_size_t size);
 
diff --git a/arch/nios2/include/asm/uaccess.h b/arch/nios2/include/asm/uaccess.h
index 6ccc9a232c23..5e6e05cc6efc 100644
--- a/arch/nios2/include/asm/uaccess.h
+++ b/arch/nios2/include/asm/uaccess.h
@@ -57,8 +57,7 @@ extern unsigned long
 raw_copy_from_user(void *to, const void __user *from, unsigned long n);
 extern unsigned long
 raw_copy_to_user(void __user *to, const void *from, unsigned long n);
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 extern long strncpy_from_user(char *__to, const char __user *__from,
 			      long __len);
diff --git a/arch/openrisc/include/asm/uaccess.h b/arch/openrisc/include/asm/uaccess.h
index d6500a374e18..db934ebc0069 100644
--- a/arch/openrisc/include/asm/uaccess.h
+++ b/arch/openrisc/include/asm/uaccess.h
@@ -218,8 +218,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long size)
 {
 	return __copy_tofrom_user((__force void *)to, from, size);
 }
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 extern unsigned long __clear_user(void __user *addr, unsigned long size);
 
diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
index 6c531d2c847e..0d17f81c8b27 100644
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -197,7 +197,6 @@ unsigned long __must_check raw_copy_to_user(void __user *dst, const void *src,
 					    unsigned long len);
 unsigned long __must_check raw_copy_from_user(void *dst, const void __user *src,
 					    unsigned long len);
-#define INLINE_COPY_TO_USER
-#define INLINE_COPY_FROM_USER
+#define INLINE_COPY_USER
 
 #endif /* __PARISC_UACCESS_H */
diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index dff035372601..a9f32c53f699 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -30,8 +30,7 @@ void debug_user_asce(int exit);
 #define uaccess_kmsan_or_inline __always_inline
 #endif
 
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 static uaccess_kmsan_or_inline __must_check unsigned long
 raw_copy_from_user(void *to, const void __user *from, unsigned long size)
diff --git a/arch/sh/include/asm/uaccess.h b/arch/sh/include/asm/uaccess.h
index a79609eb14be..02e7a066538e 100644
--- a/arch/sh/include/asm/uaccess.h
+++ b/arch/sh/include/asm/uaccess.h
@@ -95,8 +95,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	return __copy_user((__force void *)to, from, n);
 }
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 /*
  * Clear the area and return remaining number of bytes
diff --git a/arch/sparc/include/asm/uaccess_32.h b/arch/sparc/include/asm/uaccess_32.h
index 43284b6ec46a..5542d5b32994 100644
--- a/arch/sparc/include/asm/uaccess_32.h
+++ b/arch/sparc/include/asm/uaccess_32.h
@@ -190,8 +190,7 @@ static inline unsigned long raw_copy_from_user(void *to, const void __user *from
 	return __copy_user((__force void __user *) to, from, n);
 }
 
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 static inline unsigned long __clear_user(void __user *addr, unsigned long size)
 {
diff --git a/arch/sparc/include/asm/uaccess_64.h b/arch/sparc/include/asm/uaccess_64.h
index b825a5dd0210..e2989cfba626 100644
--- a/arch/sparc/include/asm/uaccess_64.h
+++ b/arch/sparc/include/asm/uaccess_64.h
@@ -231,8 +231,7 @@ unsigned long __must_check raw_copy_from_user(void *to,
 unsigned long __must_check raw_copy_to_user(void __user *to,
 					   const void *from,
 					   unsigned long size);
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 unsigned long __must_check raw_copy_in_user(void __user *to,
 					   const void __user *from,
diff --git a/arch/um/include/asm/uaccess.h b/arch/um/include/asm/uaccess.h
index 0df9ea4abda8..4417c8b1d37a 100644
--- a/arch/um/include/asm/uaccess.h
+++ b/arch/um/include/asm/uaccess.h
@@ -27,8 +27,7 @@ static inline int __access_ok(const void __user *ptr, unsigned long size);
 #define __access_ok __access_ok
 #define __clear_user __clear_user
 
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 #include <asm-generic/uaccess.h>
 
diff --git a/arch/xtensa/include/asm/uaccess.h b/arch/xtensa/include/asm/uaccess.h
index 56aec6d504fe..6538a29a2bbd 100644
--- a/arch/xtensa/include/asm/uaccess.h
+++ b/arch/xtensa/include/asm/uaccess.h
@@ -237,8 +237,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 	prefetch(from);
 	return __xtensa_copy_user((__force void *)to, from, n);
 }
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 
 /*
  * We need to return the number of bytes not cleared.  Our memset()
diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
index b276f783494c..4569045e7139 100644
--- a/include/asm-generic/uaccess.h
+++ b/include/asm-generic/uaccess.h
@@ -91,8 +91,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 	memcpy((void __force *)to, from, n);
 	return 0;
 }
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
+#define INLINE_COPY_USER
 #endif /* CONFIG_UACCESS_MEMCPY */
 
 /*
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 4fe63169d5a2..0ddd2806d7f5 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -84,7 +84,7 @@
  * the 6 functions (copy_{to,from}_user(), __copy_{to,from}_user_inatomic())
  * that are used instead.  Out of those, __... ones are inlined.  Plain
  * copy_{to,from}_user() might or might not be inlined.  If you want them
- * inlined, have asm/uaccess.h define INLINE_COPY_{TO,FROM}_USER.
+ * inlined, have asm/uaccess.h define INLINE_COPY_USER.
  *
  * NOTE: only copy_from_user() zero-pads the destination in case of short copy.
  * Neither __copy_from_user() nor __copy_from_user_inatomic() zero anything
@@ -157,7 +157,7 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
 }
 
 /*
- * Architectures that #define INLINE_COPY_TO_USER use this function
+ * Architectures that #define INLINE_COPY_USER use this function
  * directly in the normal copy_to/from_user(), the other ones go
  * through an extern _copy_to/from_user(), which expands the same code
  * here.
@@ -190,7 +190,7 @@ _inline_copy_from_user(void *to, const void __user *from, unsigned long n)
 	memset(to + (n - res), 0, res);
 	return res;
 }
-#ifndef INLINE_COPY_FROM_USER
+#ifndef INLINE_COPY_USER
 extern __must_check unsigned long
 _copy_from_user(void *, const void __user *, unsigned long);
 #endif
@@ -207,7 +207,7 @@ _inline_copy_to_user(void __user *to, const void *from, unsigned long n)
 	}
 	return n;
 }
-#ifndef INLINE_COPY_TO_USER
+#ifndef INLINE_COPY_USER
 extern __must_check unsigned long
 _copy_to_user(void __user *, const void *, unsigned long);
 #endif
@@ -217,7 +217,7 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	if (!check_copy_size(to, n, false))
 		return n;
-#ifdef INLINE_COPY_FROM_USER
+#ifdef INLINE_COPY_USER
 	return _inline_copy_from_user(to, from, n);
 #else
 	return _copy_from_user(to, from, n);
@@ -230,7 +230,7 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
 	if (!check_copy_size(from, n, true))
 		return n;
 
-#ifdef INLINE_COPY_TO_USER
+#ifdef INLINE_COPY_USER
 	return _inline_copy_to_user(to, from, n);
 #else
 	return _copy_to_user(to, from, n);
diff --git a/lib/usercopy.c b/lib/usercopy.c
index b00a3a957de6..e2f0bf104a59 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -12,15 +12,13 @@
 
 /* out-of-line parts */
 
-#if !defined(INLINE_COPY_FROM_USER)
+#if !defined(INLINE_COPY_USER)
 unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	return _inline_copy_from_user(to, from, n);
 }
 EXPORT_SYMBOL(_copy_from_user);
-#endif
 
-#if !defined(INLINE_COPY_TO_USER)
 unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	return _inline_copy_to_user(to, from, n);
diff --git a/rust/helpers/uaccess.c b/rust/helpers/uaccess.c
index d9625b9ee046..6e59cc9c665c 100644
--- a/rust/helpers/uaccess.c
+++ b/rust/helpers/uaccess.c
@@ -14,7 +14,7 @@ rust_helper_copy_to_user(void __user *to, const void *from, unsigned long n)
 	return copy_to_user(to, from, n);
 }
 
-#ifdef INLINE_COPY_FROM_USER
+#ifdef INLINE_COPY_USER
 __rust_helper
 unsigned long rust_helper__copy_from_user(void *to, const void __user *from, unsigned long n)
 {
-- 
2.43.0

Re: [PATCH 1/2] uaccess: unify inline vs outline copy_{from,to}_user() selection

Posted by Christophe Leroy (CS GROUP) 1 week ago


Le 25/03/2026 à 17:33, Yury Norov a écrit :
> The kernel allows arches to select between inline and outline
> implementations of the copy_{from,to}_user() by defining individual
> INLINE_COPY_FROM_USER and INLINE_COPY_TO_USER, correspondingly.
> However, all arches enable or disable them always together.
> 
> Without the real use-case for one helper being inlined while the other
> outlined, having independent controls is excessive and error prone.
> 
> Switch the codebase to the single unified INLINE_COPY_USER control.

Could we use a (non user selectable) Kconfig item instead, e.g. 
CONFIG_ARCH_WANT_OUTLINE_USER_COPY ?

Also, looks like only powerpc doesn't select INLINE_COPY. Would it be 
cleaner to change the logic to a flag for OUTLINE_COPY ?

Something like (untested):

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index ad7a2fe63a2a..58743cb0e305 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -186,6 +186,7 @@ config PPC
  	select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
  	select ARCH_WANT_LD_ORPHAN_WARN
  	select ARCH_WANT_OPTIMIZE_DAX_VMEMMAP	if PPC_RADIX_MMU
+	select ARCH_WANT_OUTLINE_USER_COPY
  	select ARCH_WANTS_MODULES_DATA_IN_VMALLOC	if PPC_BOOK3S_32 || PPC_8xx
  	select ARCH_WEAK_RELEASE_ACQUIRE
  	select BINFMT_ELF
diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
index b276f783494c..fb33a71fd24e 100644
--- a/include/asm-generic/uaccess.h
+++ b/include/asm-generic/uaccess.h
@@ -91,8 +91,6 @@ raw_copy_to_user(void __user *to, const void *from, 
unsigned long n)
  	memcpy((void __force *)to, from, n);
  	return 0;
  }
-#define INLINE_COPY_FROM_USER
-#define INLINE_COPY_TO_USER
  #endif /* CONFIG_UACCESS_MEMCPY */

  /*
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 1f3804245c06..bcfa8c11e49f 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -83,8 +83,8 @@
   * with that.  They should not be used directly; they are used to 
implement
   * the 6 functions (copy_{to,from}_user(), 
__copy_{to,from}_user_inatomic())
   * that are used instead.  Out of those, __... ones are inlined.  Plain
- * copy_{to,from}_user() might or might not be inlined.  If you want them
- * inlined, have asm/uaccess.h define INLINE_COPY_{TO,FROM}_USER.
+ * copy_{to,from}_user() might or might not be inlined.  If you don't 
want them
+ * inlined, select CONFIG_ARCH_WANT_OUTLINE_USER_COPY.
   *
   * NOTE: only copy_from_user() zero-pads the destination in case of 
short copy.
   * Neither __copy_from_user() nor __copy_from_user_inatomic() zero 
anything
@@ -157,8 +157,8 @@ __copy_to_user(void __user *to, const void *from, 
unsigned long n)
  }

  /*
- * Architectures that #define INLINE_COPY_TO_USER use this function
- * directly in the normal copy_to/from_user(), the other ones go
+ * Architectures that don't select CONFIG_ARCH_WANT_OUTLINE_USER_COPY 
use this
+ * function directly in the normal copy_to/from_user(), the other ones go
   * through an extern _copy_to/from_user(), which expands the same code
   * here.
   */
@@ -190,7 +190,7 @@ _inline_copy_from_user(void *to, const void __user 
*from, unsigned long n)
  	memset(to + (n - res), 0, res);
  	return res;
  }
-#ifndef INLINE_COPY_FROM_USER
+#ifndef CONFIG_ARCH_WANT_OUTLINE_USER_COPY
  extern __must_check unsigned long
  _copy_from_user(void *, const void __user *, unsigned long);
  #endif
@@ -207,7 +207,7 @@ _inline_copy_to_user(void __user *to, const void 
*from, unsigned long n)
  	}
  	return n;
  }
-#ifndef INLINE_COPY_TO_USER
+#ifndef CONFIG_ARCH_WANT_OUTLINE_USER_COPY
  extern __must_check unsigned long
  _copy_to_user(void __user *, const void *, unsigned long);
  #endif
@@ -217,7 +217,7 @@ copy_from_user(void *to, const void __user *from, 
unsigned long n)
  {
  	if (!check_copy_size(to, n, false))
  		return n;
-#ifdef INLINE_COPY_FROM_USER
+#ifndef CONFIG_ARCH_WANT_OUTLINE_USER_COPY
  	return _inline_copy_from_user(to, from, n);
  #else
  	return _copy_from_user(to, from, n);
@@ -230,7 +230,7 @@ copy_to_user(void __user *to, const void *from, 
unsigned long n)
  	if (!check_copy_size(from, n, true))
  		return n;

-#ifdef INLINE_COPY_TO_USER
+#ifndef CONFIG_ARCH_WANT_OUTLINE_USER_COPY
  	return _inline_copy_to_user(to, from, n);
  #else
  	return _copy_to_user(to, from, n);
diff --git a/lib/Kconfig b/lib/Kconfig
index 0f2fb9610647..0106c1facfa4 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -550,6 +550,9 @@ config ARCH_HAS_UACCESS_FLUSHCACHE
  config ARCH_HAS_COPY_MC
  	bool

+config ARCH_WANT_OUTLINE_USER_COPY
+	bool
+
  # Temporary. Goes away when all archs are cleaned up
  config ARCH_STACKWALK
         bool
diff --git a/lib/usercopy.c b/lib/usercopy.c
index b00a3a957de6..aa52ac3f5d6b 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -12,15 +12,13 @@

  /* out-of-line parts */

-#if !defined(INLINE_COPY_FROM_USER)
+#ifdef CONFIG_ARCH_WANT_OUTLINE_USER_COPY
  unsigned long _copy_from_user(void *to, const void __user *from, 
unsigned long n)
  {
  	return _inline_copy_from_user(to, from, n);
  }
  EXPORT_SYMBOL(_copy_from_user);
-#endif

-#if !defined(INLINE_COPY_TO_USER)
  unsigned long _copy_to_user(void __user *to, const void *from, 
unsigned long n)
  {
  	return _inline_copy_to_user(to, from, n);
diff --git a/rust/helpers/uaccess.c b/rust/helpers/uaccess.c
index d9625b9ee046..79d950425dd9 100644
--- a/rust/helpers/uaccess.c
+++ b/rust/helpers/uaccess.c
@@ -14,7 +14,7 @@ rust_helper_copy_to_user(void __user *to, const void 
*from, unsigned long n)
  	return copy_to_user(to, from, n);
  }

-#ifdef INLINE_COPY_FROM_USER
+#ifndef CONFIG_ARCH_WANT_OUTLINE_USER_COPY
  __rust_helper
  unsigned long rust_helper__copy_from_user(void *to, const void __user 
*from, unsigned long n)
  {


> 
> Reported-by: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
> Closes: https://lore.kernel.org/all/746c9c50-20c4-4dc9-a539-bf1310ff9414@kernel.org/
> Fixes: 1f9a8286bc0c ("uaccess: always export _copy_[from|to]_user with CONFIG_RUST")
> Signed-off-by: Yury Norov <ynorov@nvidia.com>


Christophe

Re: [PATCH 1/2] uaccess: unify inline vs outline copy_{from,to}_user() selection

Posted by Yury Norov 1 week ago

On Thu, Mar 26, 2026 at 02:44:40PM +0100, Christophe Leroy (CS GROUP) wrote:
> 
> 
> Le 25/03/2026 à 17:33, Yury Norov a écrit :
> > The kernel allows arches to select between inline and outline
> > implementations of the copy_{from,to}_user() by defining individual
> > INLINE_COPY_FROM_USER and INLINE_COPY_TO_USER, correspondingly.
> > However, all arches enable or disable them always together.
> > 
> > Without the real use-case for one helper being inlined while the other
> > outlined, having independent controls is excessive and error prone.
> > 
> > Switch the codebase to the single unified INLINE_COPY_USER control.
> 
> Could we use a (non user selectable) Kconfig item instead, e.g.
> CONFIG_ARCH_WANT_OUTLINE_USER_COPY ?

This sounds interesting. I need to wrap it around my head for a while.
Right now, I believe, the best solution is to isolate this setting
from the sources as much as we can, and your suggestion looks like a
step forward.

Overall, I'm puzzled why some arches enable this while the others
don't. The next question is why copy_{from,to}_user is so special.
If this function benefits from being inlined for that particular
arch or compiler, which functions would also benefit and why?

Reasoning logically, if this WANT_INLINE thing makes sense, it would
make much more sense if we create a machinery for something like:

        unsigned long __arch_inline copy_to_user();

> Also, looks like only powerpc doesn't select INLINE_COPY. Would it be
> cleaner to change the logic to a flag for OUTLINE_COPY ?

How that? x86_64 outlines it. Check it yourself:

  @@ -206,7 +206,9 @@ _inline_copy_to_user(void __user *to, const void *from, unsigned long n)
   #ifdef INLINE_COPY_USER
   # define _copy_to_user _inline_copy_to_user
   # define _copy_from_user _inline_copy_from_user
  +#error INLINE_COPY_USER
   #else
  +#error OUTLINE_COPY_USER
   extern __must_check unsigned long
   _copy_from_user(void *, const void __user *, unsigned long);

If it was really a single arch, it would be worth to discuss what for do
we need this customization at all.

Re: [PATCH 1/2] uaccess: unify inline vs outline copy_{from,to}_user() selection

Posted by Christophe Leroy (CS GROUP) 1 week ago


Le 26/03/2026 à 18:29, Yury Norov a écrit :
> On Thu, Mar 26, 2026 at 02:44:40PM +0100, Christophe Leroy (CS GROUP) wrote:
>>
>>
>> Le 25/03/2026 à 17:33, Yury Norov a écrit :
>>> The kernel allows arches to select between inline and outline
>>> implementations of the copy_{from,to}_user() by defining individual
>>> INLINE_COPY_FROM_USER and INLINE_COPY_TO_USER, correspondingly.
>>> However, all arches enable or disable them always together.
>>>
>>> Without the real use-case for one helper being inlined while the other
>>> outlined, having independent controls is excessive and error prone.
>>>
>>> Switch the codebase to the single unified INLINE_COPY_USER control.
>>
>> Could we use a (non user selectable) Kconfig item instead, e.g.
>> CONFIG_ARCH_WANT_OUTLINE_USER_COPY ?
> 
> This sounds interesting. I need to wrap it around my head for a while.
> Right now, I believe, the best solution is to isolate this setting
> from the sources as much as we can, and your suggestion looks like a
> step forward.
> 
> Overall, I'm puzzled why some arches enable this while the others
> don't. The next question is why copy_{from,to}_user is so special.
> If this function benefits from being inlined for that particular
> arch or compiler, which functions would also benefit and why?
> 
> Reasoning logically, if this WANT_INLINE thing makes sense, it would
> make much more sense if we create a machinery for something like:
> 
>          unsigned long __arch_inline copy_to_user();
> 
>> Also, looks like only powerpc doesn't select INLINE_COPY. Would it be
>> cleaner to change the logic to a flag for OUTLINE_COPY ?
> 
> How that? x86_64 outlines it. Check it yourself:
> 
>    @@ -206,7 +206,9 @@ _inline_copy_to_user(void __user *to, const void *from, unsigned long n)
>     #ifdef INLINE_COPY_USER
>     # define _copy_to_user _inline_copy_to_user
>     # define _copy_from_user _inline_copy_from_user
>    +#error INLINE_COPY_USER
>     #else
>    +#error OUTLINE_COPY_USER
>     extern __must_check unsigned long
>     _copy_from_user(void *, const void __user *, unsigned long);
> 
> If it was really a single arch, it would be worth to discuss what for do
> we need this customization at all.

Hum ... You are right. I don't know why, I thought powerpc was the only one.

Nevertheless, among the 21 architectures in arch/ , 17 of them select 
INLINE_COPY_FROM_USER, which means only 4 don't define it.

So might still be interesting to reverse the logic, then only 4 arches 
will have to select it, similar to the exemple below with powerpc:

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index ad7a2fe63a2a..58743cb0e305 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -186,6 +186,7 @@ config PPC
  	select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
  	select ARCH_WANT_LD_ORPHAN_WARN
  	select ARCH_WANT_OPTIMIZE_DAX_VMEMMAP	if PPC_RADIX_MMU
+	select ARCH_WANT_OUTLINE_USER_COPY
  	select ARCH_WANTS_MODULES_DATA_IN_VMALLOC	if PPC_BOOK3S_32 || PPC_8xx
  	select ARCH_WEAK_RELEASE_ACQUIRE
  	select BINFMT_ELF
diff --git a/lib/Kconfig b/lib/Kconfig
index 0f2fb9610647..0106c1facfa4 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -550,6 +550,9 @@ config ARCH_HAS_UACCESS_FLUSHCACHE
  config ARCH_HAS_COPY_MC
  	bool

+config ARCH_WANT_OUTLINE_USER_COPY
+	bool
+
  # Temporary. Goes away when all archs are cleaned up
  config ARCH_STACKWALK
         bool


Christophe

[PATCH 1/2] uaccess: unify inline vs outline copy_{from,to}_user() selection
[PATCH 2/2] uaccess: minimize INLINE_COPY_USER-related ifdefery