[patch V4 31/36] asm-generic: Provide generic TIF infrastructure

Thomas Gleixner
2025-09-08T21:32:32Z

Common TIF bits do not have to be defined by every architecture. They can
be defined in a generic header.

That allows adding generic TIF bits without chasing a gazillion of
architecture headers, which is again a unjustified burden on anyone who
works on generic infrastructure as it always needs a boat load of work to
keep existing architecture code working when adding new stuff.

While it is not as horrible as the ignorance of the generic entry
infrastructure, it is a welcome mechanism to make architecture people
rethink their approach of just leaching generic improvements into
architecture code and thereby making it accumulatingly harder to maintain
and improve generic code. It's about time that this changes.

Provide the infrastructure and split the TIF space in half, 16 generic and
16 architecture specific bits.

This could probably be extended by TIF_SINGLESTEP and BLOCKSTEP, but those
are only used in architecture specific code. So leave them alone for now.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

---
arch/Kconfig | 4 ++
include/asm-generic/thread_info_tif.h | 48 ++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+)

--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1730,6 +1730,10 @@ config ARCH_VMLINUX_NEEDS_RELOCS
relocations preserved. This is used by some architectures to
construct bespoke relocation tables for KASLR.

+# Select if architecture uses the common generic TIF bits
+config HAVE_GENERIC_TIF_BITS
+ bool
+
source "kernel/gcov/Kconfig"

source "scripts/gcc-plugins/Kconfig"
--- /dev/null
+++ b/include/asm-generic/thread_info_tif.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_THREAD_INFO_TIF_H_
+#define _ASM_GENERIC_THREAD_INFO_TIF_H_
+
+#include <vdso/bits.h>
+
+/* Bits 16-31 are reserved for architecture specific purposes */
+
+#define TIF_NOTIFY_RESUME 0 // callback before returning to user
+#define _TIF_NOTIFY_RESUME BIT(TIF_NOTIFY_RESUME)
+
+#define TIF_SIGPENDING 1 // signal pending
+#define _TIF_SIGPENDING BIT(TIF_SIGPENDING)
+
+#define TIF_NOTIFY_SIGNAL 2 // signal notifications exist
+#define _TIF_NOTIFY_SIGNAL BIT(TIF_NOTIFY_SIGNAL)
+
+#define TIF_MEMDIE 3 // is terminating due to OOM killer
+#define _TIF_MEMDIE BIT(TIF_MEMDIE)
+
+#define TIF_NEED_RESCHED 4 // rescheduling necessary
+#define _TIF_NEED_RESCHED BIT(TIF_NEED_RESCHED)
+
+#ifdef HAVE_TIF_NEED_RESCHED_LAZY
+# define TIF_NEED_RESCHED_LAZY 5 // Lazy rescheduling needed
+# define _TIF_NEED_RESCHED_LAZY BIT(TIF_NEED_RESCHED_LAZY)
+#endif
+
+#ifdef HAVE_TIF_POLLING_NRFLAG
+# define TIF_POLLING_NRFLAG 6 // idle is polling for TIF_NEED_RESCHED
+# define _TIF_POLLING_NRFLAG BIT(TIF_POLLING_NRFLAG)
+#endif
+
+#define TIF_USER_RETURN_NOTIFY 7 // notify kernel of userspace return
+#define _TIF_USER_RETURN_NOTIFY BIT(TIF_USER_RETURN_NOTIFY)
+
+#define TIF_UPROBE 8 // breakpointed or singlestepping
+#define _TIF_UPROBE BIT(TIF_UPROBE)
+
+#define TIF_PATCH_PENDING 9 // pending live patching update
+#define _TIF_PATCH_PENDING BIT(TIF_PATCH_PENDING)
+
+#ifdef HAVE_TIF_RESTORE_SIGMASK
+# define TIF_RESTORE_SIGMASK 10 // Restore signal mask in do_signal() */
+# define _TIF_RESTORE_SIGMASK BIT(TIF_RESTORE_SIGMASK)
+#endif
+
+#endif /* _ASM_GENERIC_THREAD_INFO_TIF_H_ */