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

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

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