[PATCH v19 10/14] arm64: syscall: Use exit-specific flags check in el0_svc_common()

[Jinjie Ruan]

The syscall exit path in el0_svc_common() re-evaluates all
_TIF_SYSCALL_WORK flags, but this mask contains flags that only
matter on entry:

- _TIF_SECCOMP: seccomp filtering is entry-only
- _TIF_SYSCALL_EMU: PTRACE_SYSEMU skips the syscall on entry

Re-checking them on exit is unnecessary and may trigger redundant work.

Switch to _TIF_SYSCALL_EXIT_WORK for the exit-path re-check to evaluate
only exit-relevant flags (_TIF_SYSCALL_TRACE, _TIF_SYSCALL_AUDIT, and
_TIF_SYSCALL_TRACEPOINT).

No functional change intended.

Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Ada Couprie Diaz <ada.coupriediaz at arm.com>
Cc: Linus Walleij <linusw at kernel.org>
Cc: Yeoreum Yun <yeoreum.yun at arm.com>
Cc: Kees Cook <kees at kernel.org>
Cc: Can Peng <pengcan at kylinos.cn>
Cc: Ryan Roberts <ryan.roberts at arm.com>
Cc: Li Qiang <liqiang01 at kylinos.cn>
Reviewed-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
Reviewed-by: Linus Walleij <linusw at kernel.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun at arm.com>
Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
 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 0061fc63e7ba..f1f0b6f3e32b 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -127,7 +127,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 	 */
 	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
 		flags = read_thread_flags();
-		if (has_syscall_work(flags) || flags & _TIF_SINGLESTEP)
+		if (unlikely(flags & _TIF_SYSCALL_EXIT_WORK) || flags & _TIF_SINGLESTEP)
 			arm64_syscall_exit_to_user_mode_work(regs);
 		return;
 	}
-- 
2.34.1