linux-kernel - Re: [PATCH v2 2/8] powerpc: Prepare to build with generic entry/exit framework

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Message-ID: <qulxc3toxkjsiljvwz23hixlxe4qrnbzekv4oqtmuch5kgzsaj@xv6oqpmhbi5w>
Date: Tue, 16 Dec 2025 20:12:09 +0530
From: Mukesh Kumar Chaurasiya <mkchauras@...ux.ibm.com>
To: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
Cc: maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
        oleg@...hat.com, kees@...nel.org, luto@...capital.net,
        wad@...omium.org, mchauras@...ux.ibm.com, thuth@...hat.com,
        sshegde@...ux.ibm.com, charlie@...osinc.com, macro@...am.me.uk,
        akpm@...ux-foundation.org, ldv@...ace.io, deller@....de,
        ankur.a.arora@...cle.com, segher@...nel.crashing.org,
        tglx@...utronix.de, thomas.weissschuh@...utronix.de,
        peterz@...radead.org, menglong8.dong@...il.com, bigeasy@...utronix.de,
        namcao@...utronix.de, kan.liang@...ux.intel.com, mingo@...nel.org,
        atrajeev@...ux.vnet.ibm.com, mark.barnett@....com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/8] powerpc: Prepare to build with generic entry/exit
 framework

On Tue, Dec 16, 2025 at 10:27:55AM +0100, Christophe Leroy (CS GROUP) wrote:
> 
> 
> Le 14/12/2025 à 14:02, Mukesh Kumar Chaurasiya a écrit :
> > From: Mukesh Kumar Chaurasiya <mchauras@...ux.ibm.com>
> > 
> > This patch introduces preparatory changes needed to support building
> > PowerPC with the generic entry/exit (irqentry) framework.
> > 
> > The following infrastructure updates are added:
> >   - Add a syscall_work field to struct thread_info to hold SYSCALL_WORK_* flags.
> >   - Provide a stub implementation of arch_syscall_is_vdso_sigreturn(),
> >     returning false for now.
> >   - Introduce on_thread_stack() helper to detect if the current stack pointer
> >     lies within the task’s kernel stack.
> > 
> > These additions enable later integration with the generic entry/exit
> > infrastructure while keeping existing PowerPC behavior unchanged.
> > 
> > No functional change is intended in 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   |  6 ++++++
> >   arch/powerpc/include/asm/syscall.h      |  5 +++++
> >   arch/powerpc/include/asm/thread_info.h  |  1 +
> >   4 files changed, 23 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 000000000000..3af16d821d07
> > --- /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
> 
> Why do you need this #ifdef ? I see no reason, the build works well without
> this #ifdef.
> 
> At the time being, CONFIG_GENERIC_IRQ_ENTRY is never selected by powerpc,
> meaning you are introducing dead code. If really needed it would be more
> explicit to add a "#if 0"
> 
Yes you are correct. I intended it to be a dead code till we introduce
the implementation. I'll remove this in next iteration.
> > +
> > +#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 6149b53b3bc8..a81a9373d723 100644
> > --- a/arch/powerpc/include/asm/stacktrace.h
> > +++ b/arch/powerpc/include/asm/stacktrace.h
> > @@ -10,4 +10,10 @@
> >   void show_user_instructions(struct pt_regs *regs);
> > +static inline bool on_thread_stack(void)
> 
> Shouldn't it be __always_inline ?
> 
Yes it should. Will fix this too.
> > +{
> > +	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 4b3c52ed6e9d..834fcc4f7b54 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 b0f200aba2b3..9c8270354f0b 100644
> > --- a/arch/powerpc/include/asm/thread_info.h
> > +++ b/arch/powerpc/include/asm/thread_info.h
> > @@ -57,6 +57,7 @@ struct thread_info {
> >   #ifdef CONFIG_SMP
> >   	unsigned int	cpu;
> >   #endif
> > +	unsigned long	syscall_work;		/* SYSCALL_WORK_ flags */
> 
> This is not used, why add it here ?
> 
I wanted it to be in a separate patch from where it's used coz if there
are any cache alignment issues, during the bisect we can be sure that
it's introduced by this variable not due to any implementation.
Do you think it should be along with the implementation?

I appreciate the review.

Regards,
Mukesh

> >   	unsigned long	local_flags;		/* private flags for thread */
> >   #ifdef CONFIG_LIVEPATCH_64
> >   	unsigned long *livepatch_sp;
>