[PATCH RESEND] syscall_user_dispatch: Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH

Currently, only x86 genuinely implements and supports Syscall User
Dispatch (SUD). Multiple architectures provide a stub
arch_syscall_is_vdso_sigreturn() returning 'false' simply to satisfy
GENERIC_ENTRY compilation, which creates a false impression of feature
support.

Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH to decouple this mechanism
from GENERIC_ENTRY. Select it exclusively on x86 and remove the redundant
stub functions from other architectures.

Link: https://lore.kernel.org/linux-arm-kernel/akZgV0Y4YAmB43_g@J2N7QTR9R3.cambridge.arm.com/
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ada Couprie Diaz <redacted>
Cc: Thomas Weißschuh <redacted>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jinjie Ruan <redacted>
---
v1 -> RESEND
- Define missing ARCH_SUPPORTS_SYSCALL_USER_DISPATCH.
---
 arch/Kconfig                         | 4 ++++
 arch/loongarch/include/asm/syscall.h | 6 ------
 arch/powerpc/include/asm/syscall.h   | 5 -----
 arch/riscv/include/asm/syscall.h     | 5 -----
 arch/s390/include/asm/syscall.h      | 5 -----
 arch/x86/Kconfig                     | 1 +
 6 files changed, 5 insertions(+), 21 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index d2dbed524f15..066263cc44fe 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig

@@ -114,8 +114,12 @@ config GENERIC_ENTRY
 	select GENERIC_IRQ_ENTRY
 	select GENERIC_SYSCALL
 
+config ARCH_SUPPORTS_SYSCALL_USER_DISPATCH
+	bool
+
 config SYSCALL_USER_DISPATCH
 	bool "Syscall User Dispatch"
+	depends on ARCH_SUPPORTS_SYSCALL_USER_DISPATCH
 	depends on GENERIC_ENTRY
 	default y
 	help

diff --git a/arch/loongarch/include/asm/syscall.h b/arch/loongarch/include/asm/syscall.h
index df8ea223c77b..d9275010f548 100644
--- a/arch/loongarch/include/asm/syscall.h
+++ b/arch/loongarch/include/asm/syscall.h

@@ -84,10 +84,4 @@ static inline int syscall_get_arch(struct task_struct *task)
 	return AUDIT_ARCH_LOONGARCH64;
 #endif
 }
-
-static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
-{
-	return false;
-}
-
 #endif	/* __ASM_LOONGARCH_SYSCALL_H */

diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index 834fcc4f7b54..4b3c52ed6e9d 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h

@@ -139,9 +139,4 @@ 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/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 8067e666a4ca..987c9a78806f 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h

@@ -112,11 +112,6 @@ static inline void syscall_handler(struct pt_regs *regs, ulong syscall)
 	regs->a0 = fn(regs);
 }
 
-static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
-{
-	return false;
-}
-
 asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);
 
 asmlinkage long sys_riscv_hwprobe(struct riscv_hwprobe *, size_t, size_t,

diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
index 4271e4169f45..5f310caad1fc 100644
--- a/arch/s390/include/asm/syscall.h
+++ b/arch/s390/include/asm/syscall.h

@@ -89,11 +89,6 @@ static inline int syscall_get_arch(struct task_struct *task)
 	return AUDIT_ARCH_S390X;
 }
 
-static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
-{
-	return false;
-}
-
 #define SYSCALL_FMT_0
 #define SYSCALL_FMT_1 , "0" (r2)
 #define SYSCALL_FMT_2 , "d" (r3) SYSCALL_FMT_1

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bdad90f210e4..f3f8ad107eeb 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig

@@ -335,6 +335,7 @@ config X86
 	select SCHED_SMT			if SMP
 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
 	select ARCH_SUPPORTS_SCHED_MC		if SMP
+	select ARCH_SUPPORTS_SYSCALL_USER_DISPATCH
 	select HAVE_SINGLE_FTRACE_DIRECT_OPS	if X86_64 && DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 
 config INSTRUCTION_DECODER

-- 
2.34.1

On Mon, Jul 13, 2026 at 11:54:22AM +0800, Jinjie Ruan wrote:

Currently, only x86 genuinely implements and supports Syscall User
Dispatch (SUD). Multiple architectures provide a stub
arch_syscall_is_vdso_sigreturn() returning 'false' simply to satisfy
GENERIC_ENTRY compilation, which creates a false impression of feature
support.

Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH to decouple this mechanism
from GENERIC_ENTRY. Select it exclusively on x86 and remove the redundant
stub functions from other architectures.

Link: https://lore.kernel.org/linux-arm-kernel/akZgV0Y4YAmB43_g@J2N7QTR9R3.cambridge.arm.com/
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ada Couprie Diaz <redacted>
Cc: Thomas Weißschuh <redacted>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jinjie Ruan <redacted>

Reviewed-by: Thomas Weißschuh <redacted>

---
v1 -> RESEND
- Define missing ARCH_SUPPORTS_SYSCALL_USER_DISPATCH.

If code is changed it is not a resend. Instead it should have been v2.

---
 arch/Kconfig                         | 4 ++++
 arch/loongarch/include/asm/syscall.h | 6 ------
 arch/powerpc/include/asm/syscall.h   | 5 -----
 arch/riscv/include/asm/syscall.h     | 5 -----
 arch/s390/include/asm/syscall.h      | 5 -----
 arch/x86/Kconfig                     | 1 +
 6 files changed, 5 insertions(+), 21 deletions(-)

(...)