[PATCH v18 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>
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 | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 0061fc63e7ba..a8e0bf8d362e 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -54,11 +54,6 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
 	syscall_set_return_value(current, regs, 0, ret);
 }
 
-static inline bool has_syscall_work(unsigned long flags)
-{
-	return unlikely(flags & _TIF_SYSCALL_WORK);
-}
-
 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 			   const syscall_fn_t syscall_table[])
 {
@@ -95,7 +90,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 		return;
 	}
 
-	if (has_syscall_work(flags)) {
+	if (unlikely(flags & _TIF_SYSCALL_WORK)) {
 		/*
 		 * The de-facto standard way to skip a system call using ptrace
 		 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
@@ -125,9 +120,9 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 	 * check again. However, if we were tracing entry, then we always trace
 	 * exit regardless, as the old entry assembly did.
 	 */
-	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
+	if (!(unlikely(flags & _TIF_SYSCALL_WORK)) && !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