linux-kernel - Re: [RFC V2 2/8] powerpc: Prepare to build with generic entry/exit framework

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Message-ID: <b347f6e2-26c0-486f-85c7-b2877b9f1189@linux.ibm.com>
Date: Sat, 13 Sep 2025 18:19:05 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Mukesh Kumar Chaurasiya <mchauras@...ux.ibm.com>
Cc: maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
        christophe.leroy@...roup.eu, oleg@...hat.com, kees@...nel.org,
        luto@...capital.net, wad@...omium.org, deller@....de, ldv@...ace.io,
        macro@...am.me.uk, charlie@...osinc.com, akpm@...ux-foundation.org,
        bigeasy@...utronix.de, ankur.a.arora@...cle.com, naveen@...nel.org,
        thomas.weissschuh@...utronix.de, Jason@...c4.com, peterz@...radead.org,
        tglx@...utronix.de, namcao@...utronix.de, kan.liang@...ux.intel.com,
        mingo@...nel.org, oliver.upton@...ux.dev, mark.barnett@....com,
        atrajeev@...ux.vnet.ibm.com, rppt@...nel.org, coltonlewis@...gle.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC V2 2/8] powerpc: Prepare to build with generic entry/exit
 framework



On 9/9/25 2:32 AM, Mukesh Kumar Chaurasiya wrote:
> Enabling build with generic entry/exit framework for powerpc
> architecture requires few necessary steps.
> 
> Introducing minor infrastructure updates to prepare for future generic
> framework handling:
> 
> - Add syscall_work field to struct thread_info for SYSCALL_WORK_* flags.
> - Provide arch_syscall_is_vdso_sigreturn() stub, returning false.
> - Add on_thread_stack() helper to test whether the current stack pointer
>    lies within the task’s kernel stack.
> 
> No functional change is intended with this patch.
> 
> Signed-off-by: Mukesh Kumar Chaurasiya <mchauras@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/entry-common.h | 11 +++++++++++
>   arch/powerpc/include/asm/stacktrace.h   |  8 ++++++++
>   arch/powerpc/include/asm/syscall.h      |  5 +++++
>   arch/powerpc/include/asm/thread_info.h  |  1 +
>   4 files changed, 25 insertions(+)
>   create mode 100644 arch/powerpc/include/asm/entry-common.h
> 
> diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h
> new file mode 100644
> index 0000000000000..3af16d821d07e
> --- /dev/null
> +++ b/arch/powerpc/include/asm/entry-common.h
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _ASM_PPC_ENTRY_COMMON_H
> +#define _ASM_PPC_ENTRY_COMMON_H
> +
> +#ifdef CONFIG_GENERIC_IRQ_ENTRY
> +
> +#include <asm/stacktrace.h>
> +
> +#endif /* CONFIG_GENERIC_IRQ_ENTRY */
> +#endif /* _ASM_PPC_ENTRY_COMMON_H */
> diff --git a/arch/powerpc/include/asm/stacktrace.h b/arch/powerpc/include/asm/stacktrace.h
> index 6149b53b3bc8e..3f0a242468813 100644
> --- a/arch/powerpc/include/asm/stacktrace.h
> +++ b/arch/powerpc/include/asm/stacktrace.h
> @@ -8,6 +8,14 @@
>   #ifndef _ASM_POWERPC_STACKTRACE_H
>   #define _ASM_POWERPC_STACKTRACE_H
>   
> +#include <linux/sched.h>

nit:

Is sched.h needed? I don't see any reference here.
It compiled for me without it.

> +
>   void show_user_instructions(struct pt_regs *regs);
>   
> +static inline bool on_thread_stack(void)
> +{
> +	return !(((unsigned long)(current->stack) ^ current_stack_pointer)
> +			& ~(THREAD_SIZE -1));
> +}
> +
>   #endif /* _ASM_POWERPC_STACKTRACE_H */
> diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
> index 4b3c52ed6e9d2..834fcc4f7b543 100644
> --- a/arch/powerpc/include/asm/syscall.h
> +++ b/arch/powerpc/include/asm/syscall.h
> @@ -139,4 +139,9 @@ static inline int syscall_get_arch(struct task_struct *task)
>   	else
>   		return AUDIT_ARCH_PPC64;
>   }
> +
> +static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
> +{
> +	return false;
> +}
>   #endif	/* _ASM_SYSCALL_H */
> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> index 2785c7462ebf7..d0e87c9bae0b0 100644
> --- a/arch/powerpc/include/asm/thread_info.h
> +++ b/arch/powerpc/include/asm/thread_info.h
> @@ -54,6 +54,7 @@
>   struct thread_info {
>   	int		preempt_count;		/* 0 => preemptable,
>   						   <0 => BUG */
> +	unsigned long	syscall_work;		/* SYSCALL_WORK_ flags */

Can this go after cpu ? it would be 8 byte aligned then. Since it is in 
fast path, might help.

>   #ifdef CONFIG_SMP
>   	unsigned int	cpu;
>   #endif