[PATCH v6 27/39] powerpc/64: context tracking remove _TIF_NOHZ

[Nicholas Piggin <npiggin@gmail.com>]

Add context tracking to the system call handler explicitly, and remove
_TIF_NOHZ.

This improves system call performance when nohz_full is enabled. On a
POWER9, gettid scv system call cost on a nohz_full CPU improves from
1129 cycles to 1004 cycles and on a housekeeping CPU from 550 cycles
to 430 cycles.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/Kconfig                   |  1 -
 arch/powerpc/include/asm/thread_info.h |  4 +---
 arch/powerpc/kernel/ptrace/ptrace.c    |  4 ----
 arch/powerpc/kernel/signal.c           |  4 ----
 arch/powerpc/kernel/syscall_64.c       | 10 ++++++++++
 5 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 107bb4319e0e..28d5a1b1510f 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -196,7 +196,6 @@ config PPC
 	select HAVE_STACKPROTECTOR		if PPC64 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r13)
 	select HAVE_STACKPROTECTOR		if PPC32 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r2)
 	select HAVE_CONTEXT_TRACKING		if PPC64
-	select HAVE_TIF_NOHZ			if PPC64
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_DYNAMIC_FTRACE
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 3d8a47af7a25..386d576673a1 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -94,7 +94,6 @@ void arch_setup_new_exec(void);
 #define TIF_PATCH_PENDING	6	/* pending live patching update */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 #define TIF_SINGLESTEP		8	/* singlestepping active */
-#define TIF_NOHZ		9	/* in adaptive nohz mode */
 #define TIF_SECCOMP		10	/* secure computing */
 #define TIF_RESTOREALL		11	/* Restore all regs (implies NOERROR) */
 #define TIF_NOERROR		12	/* Force successful syscall return */
@@ -128,11 +127,10 @@ void arch_setup_new_exec(void);
 #define _TIF_UPROBE		(1<<TIF_UPROBE)
 #define _TIF_SYSCALL_TRACEPOINT	(1<<TIF_SYSCALL_TRACEPOINT)
 #define _TIF_EMULATE_STACK_STORE	(1<<TIF_EMULATE_STACK_STORE)
-#define _TIF_NOHZ		(1<<TIF_NOHZ)
 #define _TIF_SYSCALL_EMU	(1<<TIF_SYSCALL_EMU)
 #define _TIF_SYSCALL_DOTRACE	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
 				 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT | \
-				 _TIF_NOHZ | _TIF_SYSCALL_EMU)
+				 _TIF_SYSCALL_EMU)
 
 #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
 				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 3d44b73adb83..4f3d4ff3728c 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -262,8 +262,6 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 {
 	u32 flags;
 
-	user_exit();
-
 	flags = READ_ONCE(current_thread_info()->flags) &
 		(_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
 
@@ -340,8 +338,6 @@ void do_syscall_trace_leave(struct pt_regs *regs)
 	step = test_thread_flag(TIF_SINGLESTEP);
 	if (step || test_thread_flag(TIF_SYSCALL_TRACE))
 		tracehook_report_syscall_exit(regs, step);
-
-	user_enter();
 }
 
 void __init pt_regs_check(void);
diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index 53782aa60ade..9ded046edb0e 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -282,8 +282,6 @@ static void do_signal(struct task_struct *tsk)
 
 void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 {
-	user_exit();
-
 	if (thread_info_flags & _TIF_UPROBE)
 		uprobe_notify_resume(regs);
 
@@ -299,8 +297,6 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 		tracehook_notify_resume(regs);
 		rseq_handle_notify_resume(NULL, regs);
 	}
-
-	user_enter();
 }
 
 static unsigned long get_tm_stackpointer(struct task_struct *tsk)
diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall_64.c
index dd87b2118620..d7d256a7a41f 100644
--- a/arch/powerpc/kernel/syscall_64.c
+++ b/arch/powerpc/kernel/syscall_64.c
@@ -1,9 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include <linux/context_tracking.h>
 #include <linux/err.h>
 #include <asm/asm-prototypes.h>
 #include <asm/kup.h>
 #include <asm/cputime.h>
+#include <asm/interrupt.h>
 #include <asm/hw_irq.h>
 #include <asm/interrupt.h>
 #include <asm/kprobes.h>
@@ -28,6 +30,9 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
 		BUG_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED);
 
+	CT_WARN_ON(ct_state() == CONTEXT_KERNEL);
+	user_exit_irqoff();
+
 	trace_hardirqs_off(); /* finish reconciling */
 
 	if (IS_ENABLED(CONFIG_PPC_BOOK3S))
@@ -182,6 +187,8 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 	unsigned long ti_flags;
 	unsigned long ret = 0;
 
+	CT_WARN_ON(ct_state() == CONTEXT_USER);
+
 	kuap_check_amr();
 
 	regs->result = r3;
@@ -258,8 +265,11 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 		}
 	}
 
+	user_enter_irqoff();
+
 	/* scv need not set RI=0 because SRRs are not used */
 	if (unlikely(!prep_irq_for_enabled_exit(!scv))) {
+		user_exit_irqoff();
 		local_irq_enable();
 		goto again;
 	}
-- 
2.23.0