Re: [PATCH] ARM: entry: Convert IRQ handling to generic IRQ entry

[Jinjie Ruan]

On 6/23/2026 6:52 AM, Linus Walleij wrote:
> Bring ARM to the same level of generic-ness as ARM64 by enabling
> GENERIC_IRQ_ENTRY.
> 
> Route ARM IRQ entry through C wrappers that use the generic IRQ entry
> helpers. Conversely put the FIQ entry under the generic NMI-style entry
> helpers.
> 
> Select GENERIC_IRQ_ENTRY, add the ARM entry prototypes, and provide
> regs_irqs_disabled() for the generic IRQ entry return path.
> 
> The kernel-mode IRQ return path relies on the generic IRQ entry
> preemption handling, matching the arm64 structure and avoiding the old
> assembly reschedule check.
> 
> The reschedule check is now done in raw_irqentry_exit_cond_resched()
> in kernel/entry/common.c.
> 
> User-mode IRQs __irq_usr is neither calling ct_user_exit/enter
> or asm_trace_hardirqs_off/on anymore. The corresponding calls happen on
> irqentry_enter/exit() call paths, e.g the irq-disabled C variants
> __ct_user_exit/enter() are called instead.
> 
> As __irq_usr no longer returns by jumping to ret_to_user_from_irq,
> the corresponding code has been inlined, except the slow_work_pending
> part, which is now also handled by generic entry. ret_to_user_from_irq
> is only called from v7m so it has been renamed accordingly.
> 
> arch_do_signal_or_restart() is required, but we only need a very small
> stub, since we keep the existing syscall restart code around in assembly.
> 
> Tested on with multi_v7_defconfig and qemu-system-arm vexpress-a15
> using vexpress-v2p-ca15-tc1.dtb and some different loads.
> 
> A note on V7M: the reason we cannot switch the V7M entry over to generic
> entry is that it raises a "pendable service call" ("pendv") exception to
> process deferred work at the end of the interrupt handler. This is done
> so higher priority work can come in. This has no corresponding structure
> in other ARM cores.
> 
> This is a reduced patch based on the earlier generic entry series avoiding
> all the syscall handling changes.
> 
> Link: https://lore.kernel.org/linux-arm-kernel/20250420-arm-generic-entry-v6-0-95f1fcdfeeb2@xxxxxxxxxx/
> Signed-off-by: Linus Walleij <linusw@xxxxxxxxxx>
> ---
>  arch/arm/Kconfig                    |  1 +
>  arch/arm/include/asm/entry-common.h |  7 ++++
>  arch/arm/include/asm/entry.h        | 10 +++++
>  arch/arm/include/asm/ptrace.h       |  7 +++-
>  arch/arm/kernel/Makefile            |  2 +-
>  arch/arm/kernel/entry-armv.S        | 75 ++++++++-----------------------------
>  arch/arm/kernel/entry-common.S      |  5 ++-
>  arch/arm/kernel/entry-header.S      |  7 +++-
>  arch/arm/kernel/entry-v7m.S         |  2 +-
>  arch/arm/kernel/entry.c             | 51 +++++++++++++++++++++++++
>  arch/arm/kernel/irq.c               |  6 +++
>  arch/arm/kernel/irq.h               |  2 +
>  arch/arm/kernel/signal.c            |  6 +++
>  13 files changed, 116 insertions(+), 65 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 73e6647bea46..aad21d645ff3 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -71,6 +71,7 @@ config ARM
>  	select GENERIC_CPU_AUTOPROBE
>  	select GENERIC_CPU_DEVICES
>  	select GENERIC_EARLY_IOREMAP
> +	select GENERIC_IRQ_ENTRY if !CPU_V7M
>  	select GENERIC_IDLE_POLL_SETUP
>  	select GENERIC_IRQ_MULTI_HANDLER
>  	select GENERIC_IRQ_PROBE
> diff --git a/arch/arm/include/asm/entry-common.h b/arch/arm/include/asm/entry-common.h
> new file mode 100644
> index 000000000000..c017df5f39d5
> --- /dev/null
> +++ b/arch/arm/include/asm/entry-common.h
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_ARM_ENTRY_COMMON_H
> +#define __ASM_ARM_ENTRY_COMMON_H
> +
> +#include <asm/stacktrace.h>
> +
> +#endif
> diff --git a/arch/arm/include/asm/entry.h b/arch/arm/include/asm/entry.h
> new file mode 100644
> index 000000000000..864c9b3abbf1
> --- /dev/null
> +++ b/arch/arm/include/asm/entry.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef __ASM_ENTRY_H__
> +#define __ASM_ENTRY_H__
> +
> +struct pt_regs;
> +
> +void arm_irq_handler(struct pt_regs *regs, int mode);
> +void arm_fiq_handler(struct pt_regs *regs);
> +
> +#endif /* __ASM_ENTRY_H__ */
> diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
> index 6eb311fb2da0..88ddb9371a02 100644
> --- a/arch/arm/include/asm/ptrace.h
> +++ b/arch/arm/include/asm/ptrace.h
> @@ -46,8 +46,13 @@ struct svc_pt_regs {
>  #define processor_mode(regs) \
>  	((regs)->ARM_cpsr & MODE_MASK)
>  
> +static inline bool regs_irqs_disabled(const struct pt_regs *regs)
> +{
> +	return regs->ARM_cpsr & PSR_I_BIT;
> +}
> +
>  #define interrupts_enabled(regs) \
> -	(!((regs)->ARM_cpsr & PSR_I_BIT))
> +	(!regs_irqs_disabled(regs))
>  
>  #define fast_interrupts_enabled(regs) \
>  	(!((regs)->ARM_cpsr & PSR_F_BIT))
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index b36cf0cfd4a7..3b8a62f6f54d 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -17,7 +17,7 @@ CFLAGS_REMOVE_return_address.o = -pg
>  
>  # Object file lists.
>  
> -obj-y		:= elf.o entry-common.o irq.o opcodes.o \
> +obj-y		:= elf.o entry.o entry-common.o irq.o opcodes.o \
>  		   process.o ptrace.o reboot.o io.o \
>  		   setup.o signal.o sigreturn_codes.o \
>  		   stacktrace.o sys_arm.o time.o traps.o
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index a3d050ce9b79..8ac7f1512ee8 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -36,35 +36,6 @@
>  #define RELOC_TEXT_NONE
>  #endif
>  
> -/*
> - * Interrupt handling.
> - */
> -	.macro	irq_handler, from_user:req
> -	mov	r1, sp
> -	ldr_this_cpu r2, irq_stack_ptr, r2, r3
> -	.if	\from_user == 0
> -	@
> -	@ If we took the interrupt while running in the kernel, we may already
> -	@ be using the IRQ stack, so revert to the original value in that case.
> -	@
> -	subs	r3, r2, r1		@ SP above bottom of IRQ stack?
> -	rsbscs	r3, r3, #THREAD_SIZE	@ ... and below the top?
> -#ifdef CONFIG_VMAP_STACK
> -	ldr_va	r3, high_memory, cc	@ End of the linear region
> -	cmpcc	r3, r1			@ Stack pointer was below it?
> -#endif
> -	bcc	0f			@ If not, switch to the IRQ stack
> -	mov	r0, r1
> -	bl	generic_handle_arch_irq
> -	b	1f
> -0:
> -	.endif
> -
> -	mov_l	r0, generic_handle_arch_irq
> -	bl	call_with_stack
> -1:
> -	.endm
> -
>  	.macro	pabt_helper
>  	@ PABORT handler takes pt_regs in r2, fault address in r4 and psr in r5
>  #ifdef MULTI_PABORT
> @@ -224,34 +195,17 @@ ENDPROC(__dabt_svc)
>  
>  	.align	5
>  __irq_svc:
> -	svc_entry
> -	irq_handler from_user=0
> -
> -#ifdef CONFIG_PREEMPTION
> -	ldr	r8, [tsk, #TI_PREEMPT]		@ get preempt count
> -	ldr	r0, [tsk, #TI_FLAGS]		@ get flags
> -	teq	r8, #0				@ if preempt count != 0
> -	movne	r0, #0				@ force flags to 0
> -	tst	r0, #_TIF_NEED_RESCHED
> -	blne	svc_preempt
> -#endif
> +	svc_entry trace=0
> +	mov	r0, sp				@ regs
> +	mov	r1, #0				@ from kernel mode
> +	bl	arm_irq_handler
>  
> -	svc_exit r5, irq = 1			@ return from exception
> +	svc_exit r5, irqentry = 1		@ return from exception
>   UNWIND(.fnend		)
>  ENDPROC(__irq_svc)
>  
>  	.ltorg
>  
> -#ifdef CONFIG_PREEMPTION
> -svc_preempt:
> -	mov	r8, lr
> -1:	bl	preempt_schedule_irq		@ irq en/disable is done inside
> -	ldr	r0, [tsk, #TI_FLAGS]		@ get new tasks TI_FLAGS
> -	tst	r0, #_TIF_NEED_RESCHED
> -	reteq	r8				@ go again
> -	b	1b
> -#endif
> -
>  __und_fault:
>  	@ Correct the PC such that it is pointing at the instruction
>  	@ which caused the fault.  If the faulting instruction was ARM
> @@ -302,7 +256,7 @@ ENDPROC(__pabt_svc)
>  __fiq_svc:
>  	svc_entry trace=0
>  	mov	r0, sp				@ struct pt_regs *regs
> -	bl	handle_fiq_as_nmi
> +	bl	arm_fiq_handler
>  	svc_exit_via_fiq
>   UNWIND(.fnend		)
>  ENDPROC(__fiq_svc)
> @@ -331,7 +285,7 @@ __fiq_abt:
>  	stmfd	sp!, {r1 - r2}
>  
>  	add	r0, sp, #8			@ struct pt_regs *regs
> -	bl	handle_fiq_as_nmi
> +	bl	arm_fiq_handler
>  
>  	ldmfd	sp!, {r1 - r2}
>   ARM(	msr	cpsr_c, #ABT_MODE | PSR_I_BIT | PSR_F_BIT )
> @@ -438,12 +392,15 @@ ENDPROC(__dabt_usr)
>  
>  	.align	5
>  __irq_usr:
> -	usr_entry
> +	usr_entry trace=0
>  	kuser_cmpxchg_check
> -	irq_handler from_user=1
> -	get_thread_info tsk
> -	mov	why, #0
> -	b	ret_to_user_from_irq
> +	mov	r0, sp				@ regs
> +	mov	r1, #1				@ from user mode
> +	bl	arm_irq_handler
> +#ifdef CONFIG_KSTACK_ERASE
> +	bl	stackleak_erase_on_task_stack
> +#endif
> +	restore_user_regs fast = 0, offset = 0
>   UNWIND(.fnend		)
>  ENDPROC(__irq_usr)
>  
> @@ -498,7 +455,7 @@ __fiq_usr:
>  	usr_entry trace=0
>  	kuser_cmpxchg_check
>  	mov	r0, sp				@ struct pt_regs *regs
> -	bl	handle_fiq_as_nmi
> +	bl	arm_fiq_handler
>  	get_thread_info tsk
>  	restore_user_regs fast = 0, offset = 0
>   UNWIND(.fnend		)
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index 88336a1292bb..d5fdb234c1d4 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -110,7 +110,8 @@ ret_slow_syscall:
>  	bl	do_rseq_syscall
>  #endif
>  	disable_irq_notrace			@ disable interrupts
> -ENTRY(ret_to_user_from_irq)
> +ENTRY(v7m_ret_to_user_from_irq)
> +	/* Only the v7m jumps directly to v7m_ret_to_user_from_irq */
>  	ldr	r1, [tsk, #TI_FLAGS]
>  	movs	r1, r1, lsl #16
>  	bne	slow_work_pending
> @@ -123,7 +124,7 @@ no_work_pending:
>  	bl	stackleak_erase_on_task_stack
>  #endif
>  	restore_user_regs fast = 0, offset = 0
> -ENDPROC(ret_to_user_from_irq)
> +ENDPROC(v7m_ret_to_user_from_irq)
>  ENDPROC(ret_to_user)
>  
>  /*
> diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
> index 99411fa91350..e83f2fb8a592 100644
> --- a/arch/arm/kernel/entry-header.S
> +++ b/arch/arm/kernel/entry-header.S
> @@ -199,7 +199,11 @@
>  	.endm
>  
>  
> -	.macro	svc_exit, rpsr, irq = 0
> +	.macro	svc_exit, rpsr, irq = 0, irqentry = 0
> +	.if	\irqentry != 0
> +	@ Generic IRQ entry already handled tracing and lockdep state.
> +	disable_irq_notrace
> +	.else
>  	.if	\irq != 0
>  	@ IRQs already off
>  #ifdef CONFIG_TRACE_IRQFLAGS
> @@ -216,6 +220,7 @@
>  	tst	\rpsr, #PSR_I_BIT
>  	blne	trace_hardirqs_off
>  #endif
> +	.endif
>  	.endif
>  	uaccess_exit tsk, r0, r1
>  
> diff --git a/arch/arm/kernel/entry-v7m.S b/arch/arm/kernel/entry-v7m.S
> index 52bacf07ba16..49a3a34e2913 100644
> --- a/arch/arm/kernel/entry-v7m.S
> +++ b/arch/arm/kernel/entry-v7m.S
> @@ -94,7 +94,7 @@ __pendsv_entry:
>  	@ execute the pending work, including reschedule
>  	get_thread_info tsk
>  	mov	why, #0
> -	b	ret_to_user_from_irq
> +	b	v7m_ret_to_user_from_irq
>  ENDPROC(__pendsv_entry)
>  
>  /*
> diff --git a/arch/arm/kernel/entry.c b/arch/arm/kernel/entry.c
> new file mode 100644
> index 000000000000..1142e418d161
> --- /dev/null
> +++ b/arch/arm/kernel/entry.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/hardirq.h>
> +#include <linux/irq-entry-common.h>
> +#include <linux/irq.h>
> +
> +#include <asm/entry.h>
> +#include <asm/stacktrace.h>
> +#include <asm/traps.h>
> +
> +#include "irq.h"
> +
> +static void noinstr handle_arm_irq(void *data)
> +{
> +	struct pt_regs *regs = data;
> +	struct pt_regs *old_regs;
> +
> +	irq_enter_rcu();
> +	old_regs = set_irq_regs(regs);
> +
> +	handle_arch_irq(regs);
> +
> +	set_irq_regs(old_regs);
> +	irq_exit_rcu();
> +}
> +
> +noinstr void arm_irq_handler(struct pt_regs *regs, int mode)
> +{
> +	irqentry_state_t state = irqentry_enter(regs);
> +
> +	/*
> +	 * mode == 1 means we came from userspace, and then we
> +	 * should just immediately switch to the irq stack.
> +	 * Then we check of we are on the thread stack. If we are
> +	 * not, then by definition we are already using the irq stack.
> +	 */
> +	if (mode == 1 || on_thread_stack())
> +		call_on_irq_stack(handle_arm_irq, regs);

It seems that the CONFIG_VMAP_STACK Overflow Protection is missing,
should we implement the C version of CONFIG_VMAP_STACK first, before
moving the IRQ handling to C?"

-       .macro  irq_handler, from_user:req
-#ifdef CONFIG_VMAP_STACK
-       ldr_va  r3, high_memory, cc     @ End of the linear region
-       cmpcc   r3, r1                  @ Stack pointer was below it?
-#endif


> +	else
> +		handle_arm_irq(regs);
> +
> +	irqentry_exit(regs, state);
> +}
> +
> +noinstr void arm_fiq_handler(struct pt_regs *regs)
> +{
> +	irqentry_state_t state = irqentry_nmi_enter(regs);
> +
> +	handle_fiq_as_nmi(regs);
> +
> +	irqentry_nmi_exit(regs, state);
> +}
> diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
> index e1993e28a9ec..f99d6b24d8ff 100644
> --- a/arch/arm/kernel/irq.c
> +++ b/arch/arm/kernel/irq.c
> @@ -43,6 +43,7 @@
>  #include <asm/mach/irq.h>
>  #include <asm/mach/time.h>
>  
> +#include "irq.h"
>  #include "reboot.h"
>  
>  unsigned long irq_err_count;
> @@ -71,6 +72,11 @@ static void __init init_irq_stacks(void)
>  	}
>  }
>  
> +void call_on_irq_stack(void (*fn)(void *), void *arg)
> +{
> +	call_with_stack(fn, arg, __this_cpu_read(irq_stack_ptr));
> +}
> +
>  #ifdef CONFIG_SOFTIRQ_ON_OWN_STACK
>  static void ____do_softirq(void *arg)
>  {
> diff --git a/arch/arm/kernel/irq.h b/arch/arm/kernel/irq.h
> new file mode 100644
> index 000000000000..80dd5bfe6403
> --- /dev/null
> +++ b/arch/arm/kernel/irq.h
> @@ -0,0 +1,2 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +void call_on_irq_stack(void (*fn)(void *), void *arg);
> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
> index 7be9188d83d9..9084c04c07f7 100644
> --- a/arch/arm/kernel/signal.c
> +++ b/arch/arm/kernel/signal.c
> @@ -12,6 +12,7 @@
>  #include <linux/resume_user_mode.h>
>  #include <linux/uprobes.h>
>  #include <linux/syscalls.h>
> +#include <linux/irq-entry-common.h>
>  
>  #include <asm/elf.h>
>  #include <asm/cacheflush.h>
> @@ -599,6 +600,11 @@ static int do_signal(struct pt_regs *regs, int syscall)
>  	return 0;
>  }
>  
> +void arch_do_signal_or_restart(struct pt_regs *regs)
> +{
> +	do_signal(regs, 0);
> +}
> +
>  asmlinkage int
>  do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
>  {
> 
> ---
> base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6
> change-id: 20260622-arm-generic-irq-entry-v7-1-ff6c1d6c9c48
> 
> Best regards,
> --  
> Linus Walleij <linusw@xxxxxxxxxx>
> 
> 
>