linux-kernel - [PATCH] arm64: add unlikely hint to MTE async fault check in el0_svc

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Message-Id: <20250919033327.1942730-1-liqiang01@kylinos.cn>
Date: Fri, 19 Sep 2025 11:33:27 +0800
From: Li Qiang <liqiang01@...inos.cn>
To: catalin.marinas@....com,
	will@...nel.org
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Li Qiang <liqiang01@...inos.cn>
Subject: [PATCH] arm64: add unlikely hint to MTE async fault check in el0_svc_common

Add unlikely() hint to the _TIF_MTE_ASYNC_FAULT flag check in
el0_svc_common() since asynchronous MTE faults are expected to be
rare occurrences during normal system call execution.

This optimization helps the compiler to improve instruction caching
and branch prediction for the common case where no asynchronous
MTE faults are pending, while maintaining correct behavior for
the exceptional case where such faults need to be handled prior
to system call execution.

Signed-off-by: Li Qiang <liqiang01@...inos.cn>
---
 arch/arm64/kernel/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index c442fcec6b9e..7eb13f4c87da 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -96,7 +96,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 	 * (Similarly for HVC and SMC elsewhere.)
 	 */

-	if (flags & _TIF_MTE_ASYNC_FAULT) {
+	if (unlikely(flags & _TIF_MTE_ASYNC_FAULT)) {
 		/*
 		 * Process the asynchronous tag check fault before the actual
 		 * syscall. do_notify_resume() will send a signal to userspace
-- 
2.25.1