[PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

[PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

[Ilya Leoshkevich]

Inline KMSAN arch_local_irq_*() definitions run afoul of
-Wstatic-in-inline. Move them out-of-line. Decompressor is not
instrumented, so make sure it keeps using inline definitions.
Make sure non-GPL modules see the out-of-line definitions.

Cc: Boqun Feng <boqun@kernel.org>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202607131219.euJHPSJ5-lkp@intel.com/
Suggested-by: Heiko Carstens <hca@linux.ibm.com>
Fixes: 1b301f5f28ba ("s390/irqflags: do not instrument arch_local_irq_*() with KMSAN")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/include/asm/irqflags.h | 20 +++++++++++++-------
 arch/s390/kernel/Makefile        |  1 +
 arch/s390/kernel/irqflags.c      | 27 +++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 7 deletions(-)
 create mode 100644 arch/s390/kernel/irqflags.c

diff --git a/arch/s390/include/asm/irqflags.h b/arch/s390/include/asm/irqflags.h
index bcab456dfb803..44d158f7831e6 100644
--- a/arch/s390/include/asm/irqflags.h
+++ b/arch/s390/include/asm/irqflags.h
@@ -37,18 +37,24 @@ static __always_inline void __arch_local_irq_ssm(unsigned long flags)
 	asm volatile("ssm   %0" : : "Q" (flags) : "memory");
 }
 
-#ifdef CONFIG_KMSAN
-#define arch_local_irq_attributes noinline notrace __no_sanitize_memory __maybe_unused
+#if defined(CONFIG_KMSAN) && !defined(__DECOMPRESSOR)
+extern unsigned long arch_local_save_flags(void);
+extern unsigned long arch_local_irq_save(void);
+extern void arch_local_irq_enable_external(void);
+extern void arch_local_irq_enable(void);
 #else
-#define arch_local_irq_attributes __always_inline
+#define arch_local_save_flags __arch_local_save_flags
+#define arch_local_irq_save __arch_local_irq_save
+#define arch_local_irq_enable_external __arch_local_irq_enable_external
+#define arch_local_irq_enable __arch_local_irq_enable
 #endif
 
-static arch_local_irq_attributes unsigned long arch_local_save_flags(void)
+static __always_inline unsigned long __arch_local_save_flags(void)
 {
 	return __arch_local_irq_stnsm(0xff);
 }
 
-static arch_local_irq_attributes unsigned long arch_local_irq_save(void)
+static __always_inline unsigned long __arch_local_irq_save(void)
 {
 	return __arch_local_irq_stnsm(0xfc);
 }
@@ -58,12 +64,12 @@ static __always_inline void arch_local_irq_disable(void)
 	arch_local_irq_save();
 }
 
-static arch_local_irq_attributes void arch_local_irq_enable_external(void)
+static __always_inline void __arch_local_irq_enable_external(void)
 {
 	__arch_local_irq_stosm(0x01);
 }
 
-static arch_local_irq_attributes void arch_local_irq_enable(void)
+static __always_inline void __arch_local_irq_enable(void)
 {
 	__arch_local_irq_stosm(0x03);
 }
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index 6c88476d79a31..14ef03cb2f72a 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -72,6 +72,7 @@ obj-$(CONFIG_STACKPROTECTOR)	+= stackprotector.o
 obj-$(CONFIG_KEXEC_FILE)	+= machine_kexec_file.o kexec_image.o
 obj-$(CONFIG_KEXEC_FILE)	+= kexec_elf.o
 obj-$(CONFIG_CERT_STORE)	+= cert_store.o
+obj-$(CONFIG_KMSAN)		+= irqflags.o
 
 obj-$(CONFIG_PERF_EVENTS)	+= perf_event.o
 obj-$(CONFIG_PERF_EVENTS)	+= perf_cpum_cf.o perf_cpum_sf.o
diff --git a/arch/s390/kernel/irqflags.c b/arch/s390/kernel/irqflags.c
new file mode 100644
index 0000000000000..98299c4758c6e
--- /dev/null
+++ b/arch/s390/kernel/irqflags.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <asm/irqflags.h>
+#include <linux/export.h>
+
+noinstr unsigned long arch_local_save_flags(void)
+{
+	return __arch_local_save_flags();
+}
+EXPORT_SYMBOL(arch_local_save_flags);
+
+noinstr unsigned long arch_local_irq_save(void)
+{
+	return __arch_local_irq_save();
+}
+EXPORT_SYMBOL(arch_local_irq_save);
+
+noinstr void arch_local_irq_enable_external(void)
+{
+	__arch_local_irq_enable_external();
+}
+EXPORT_SYMBOL(arch_local_irq_enable_external);
+
+noinstr void arch_local_irq_enable(void)
+{
+	__arch_local_irq_enable();
+}
+EXPORT_SYMBOL(arch_local_irq_enable);
-- 
2.55.0

Re: [PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

[Heiko Carstens]

On Thu, Aug 06, 2026 at 12:00:19PM +0200, Ilya Leoshkevich wrote:
> Inline KMSAN arch_local_irq_*() definitions run afoul of
> -Wstatic-in-inline. Move them out-of-line. Decompressor is not
> instrumented, so make sure it keeps using inline definitions.
> Make sure non-GPL modules see the out-of-line definitions.
> 
> Cc: Boqun Feng <boqun@kernel.org>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202607131219.euJHPSJ5-lkp@intel.com/
> Suggested-by: Heiko Carstens <hca@linux.ibm.com>
> Fixes: 1b301f5f28ba ("s390/irqflags: do not instrument arch_local_irq_*() with KMSAN")
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  arch/s390/include/asm/irqflags.h | 20 +++++++++++++-------
>  arch/s390/kernel/Makefile        |  1 +
>  arch/s390/kernel/irqflags.c      | 27 +++++++++++++++++++++++++++
>  3 files changed, 41 insertions(+), 7 deletions(-)
>  create mode 100644 arch/s390/kernel/irqflags.c

Don't we have the very same problem in arch/s390/include/asm/uaccess.h
with uaccess_kmsan_or_inline too?

> -#ifdef CONFIG_KMSAN
> -#define arch_local_irq_attributes noinline notrace __no_sanitize_memory __maybe_unused
> +#if defined(CONFIG_KMSAN) && !defined(__DECOMPRESSOR)
> +extern unsigned long arch_local_save_flags(void);
> +extern unsigned long arch_local_irq_save(void);
> +extern void arch_local_irq_enable_external(void);
> +extern void arch_local_irq_enable(void);

FWIW, we go without "extern" for function prototypes.

>  #else
> -#define arch_local_irq_attributes __always_inline
> +#define arch_local_save_flags __arch_local_save_flags
> +#define arch_local_irq_save __arch_local_irq_save
> +#define arch_local_irq_enable_external __arch_local_irq_enable_external
> +#define arch_local_irq_enable __arch_local_irq_enable
>  #endif

For the sake of readability: could you adjust all of them with tabs?
Like e.g.:

#define arch_local_save_flags		__arch_local_save_flags
#define arch_local_irq_save		__arch_local_irq_save
#define arch_local_irq_enable_external	__arch_local_irq_enable_external
#define arch_local_irq_enable		__arch_local_irq_enable

And just to annoy you: the patch subject needs to be adjusted to:

s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN
               ^

In the meantime we require always an upper case letter following the
component.

> +++ b/arch/s390/kernel/irqflags.c
> @@ -0,0 +1,27 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <asm/irqflags.h>
> +#include <linux/export.h>

Please add an empty line before the first include, and also change the order
of includes - "linux" should always come before "asm".

Re: [PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

[Ilya Leoshkevich]

On 8/6/26 12:17, Heiko Carstens wrote:
> On Thu, Aug 06, 2026 at 12:00:19PM +0200, Ilya Leoshkevich wrote:
>> Inline KMSAN arch_local_irq_*() definitions run afoul of
>> -Wstatic-in-inline. Move them out-of-line. Decompressor is not
>> instrumented, so make sure it keeps using inline definitions.
>> Make sure non-GPL modules see the out-of-line definitions.
>>
>> Cc: Boqun Feng <boqun@kernel.org>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202607131219.euJHPSJ5-lkp@intel.com/
>> Suggested-by: Heiko Carstens <hca@linux.ibm.com>
>> Fixes: 1b301f5f28ba ("s390/irqflags: do not instrument arch_local_irq_*() with KMSAN")
>> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
>> ---
>>   arch/s390/include/asm/irqflags.h | 20 +++++++++++++-------
>>   arch/s390/kernel/Makefile        |  1 +
>>   arch/s390/kernel/irqflags.c      | 27 +++++++++++++++++++++++++++
>>   3 files changed, 41 insertions(+), 7 deletions(-)
>>   create mode 100644 arch/s390/kernel/irqflags.c
> 
> Don't we have the very same problem in arch/s390/include/asm/uaccess.h
> with uaccess_kmsan_or_inline too?

Apparently yes. I will send a separate patch.


And I'll fix the rest of your findings in v2.

Re: [PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Missing KMSAN attributes on the `extern` declarations of `arch_local_save_flags` and `arch_local_irq_save` will cause spurious use-of-uninitialized-value reports.
--

--- Patch [1]: [PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN ---
commit 75ac5ab83800e65155075aeee91b3fd23aa6274d
Author: Ilya Leoshkevich <iii@linux.ibm.com>

s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

This commit moves KMSAN arch_local_irq_*() definitions out-of-line to avoid
warnings about static functions in inline functions. Uninstrumented
decompressor code keeps the inline definitions, while non-GPL modules see
the out-of-line versions.

Closes: https://lore.kernel.org/oe-kbuild-all/202607131219.euJHPSJ5-lkp@intel.com/

> diff --git a/arch/s390/include/asm/irqflags.h b/arch/s390/include/asm/irqflags.h
> index bcab456dfb803..44d158f7831e6 100644
> --- a/arch/s390/include/asm/irqflags.h
> +++ b/arch/s390/include/asm/irqflags.h
> @@ -37,18 +37,24 @@ static __always_inline void __arch_local_irq_ssm(unsigned long flags)
>  	asm volatile("ssm   %0" : : "Q" (flags) : "memory");
>  }
>  
> -#ifdef CONFIG_KMSAN
> -#define arch_local_irq_attributes noinline notrace __no_sanitize_memory __maybe_unused
> +#if defined(CONFIG_KMSAN) && !defined(__DECOMPRESSOR)
> +extern unsigned long arch_local_save_flags(void);
> +extern unsigned long arch_local_irq_save(void);

[Severity: High]
Since these extern declarations lack KMSAN attributes, will instrumented
callers expect a populated return value shadow in __msan_retval_tls?

When arch_local_save_flags() and arch_local_irq_save() are called from
instrumented code, the caller reads __msan_retval_tls. However, because the
corresponding definitions are marked noinstr:

arch/s390/kernel/irqflags.c:
noinstr unsigned long arch_local_save_flags(void)
{
	return __arch_local_save_flags();
}

instrumentation is skipped, and __msan_retval_tls is never populated before
returning to the caller. 

Could this result in spurious use-of-uninitialized-value reports on every
IRQ state check or lock operation (like spin_lock_irqsave) when the kernel
is built with CONFIG_KMSAN?

> +extern void arch_local_irq_enable_external(void);
> +extern void arch_local_irq_enable(void);
>  #else
> -#define arch_local_irq_attributes __always_inline
> +#define arch_local_save_flags __arch_local_save_flags
> +#define arch_local_irq_save __arch_local_irq_save

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260806100038.3163298-1-iii@linux.ibm.com?part=1

Re: [PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

[Ilya Leoshkevich]

On 8/6/26 12:19, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Missing KMSAN attributes on the `extern` declarations of `arch_local_save_flags` and `arch_local_irq_save` will cause spurious use-of-uninitialized-value reports.

[...]

>> -#ifdef CONFIG_KMSAN
>> -#define arch_local_irq_attributes noinline notrace __no_sanitize_memory __maybe_unused
>> +#if defined(CONFIG_KMSAN) && !defined(__DECOMPRESSOR)
>> +extern unsigned long arch_local_save_flags(void);
>> +extern unsigned long arch_local_irq_save(void);
> 
> [Severity: High]
> Since these extern declarations lack KMSAN attributes, will instrumented
> callers expect a populated return value shadow in __msan_retval_tls?
> 
> When arch_local_save_flags() and arch_local_irq_save() are called from
> instrumented code, the caller reads __msan_retval_tls. However, because the
> corresponding definitions are marked noinstr:
> 
> arch/s390/kernel/irqflags.c:
> noinstr unsigned long arch_local_save_flags(void)
> {
> 	return __arch_local_save_flags();
> }
> 
> instrumentation is skipped, and __msan_retval_tls is never populated before
> returning to the caller.
> 
> Could this result in spurious use-of-uninitialized-value reports on every
> IRQ state check or lock operation (like spin_lock_irqsave) when the kernel
> is built with CONFIG_KMSAN?

This is a known issue that affects many other places.
It can be resolved by compiling with KMSAN_CHECK_PARAM_RETVAL:


lib/Kconfig.kmsan:
------------------
Disabling KMSAN_CHECK_PARAM_RETVAL will result in tracking shadow for
function parameters and return values across function borders. This
is a more relaxed mode, but it generates more instrumentation code and
may potentially report errors in corner cases when non-instrumented
functions call instrumented ones.


LLVM refers to this as "EagerChecks" internally.

[...]