linux-kernel - Re: [patch V2 31/37] asm-generic: Provide generic TIF infrastructure

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Message-ID: <ed52565a-be0b-45a7-a838-a9c6f8d5359d@efficios.com>
Date: Mon, 25 Aug 2025 15:33:25 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
 Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney"
 <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson
 <seanjc@...gle.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>, x86@...nel.org,
 Heiko Carstens <hca@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Huacai Chen <chenhuacai@...nel.org>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [patch V2 31/37] asm-generic: Provide generic TIF infrastructure

On 2025-08-23 12:40, Thomas Gleixner wrote:
> 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 changea.

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@...utronix.de>
> Cc: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

> ---
>   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_ */
> 


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com