powerpc/64: context tracking remove _TIF_NOHZ

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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210130130852.2952424-31-npiggin@gmail.com

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

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 | \

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);

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)

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))
@@ -144,7 +149,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
  * enabled when the interrupt handler returns (indicating a process-context /
  * synchronous interrupt) then irqs_enabled should be true.
  */
-static notrace inline bool prep_irq_for_enabled_exit(bool clear_ri, bool irqs_enabled)
+static notrace inline bool __prep_irq_for_enabled_exit(bool clear_ri)
 {
 	/* This must be done with RI=1 because tracing may touch vmaps */
 	trace_hardirqs_on();
@@ -161,29 +166,6 @@ static notrace inline bool prep_irq_for_enabled_exit(bool clear_ri, bool irqs_en
 		trace_hardirqs_off();
 		local_paca->irq_happened |= PACA_IRQ_HARD_DIS;
 
-		/*
-		 * Must replay pending soft-masked interrupts now. Don't just
-		 * local_irq_enabe(); local_irq_disable(); because if we are
-		 * returning from an asynchronous interrupt here, another one
-		 * might hit after irqs are enabled, and it would exit via this
-		 * same path allowing another to fire, and so on unbounded.
-		 *
-		 * If interrupts were enabled when this interrupt exited,
-		 * indicating a process context (synchronous) interrupt,
-		 * local_irq_enable/disable can be used, which will enable
-		 * interrupts rather than keeping them masked (unclear how
-		 * much benefit this is over just replaying for all cases,
-		 * because we immediately disable again, so all we're really
-		 * doing is allowing hard interrupts to execute directly for
-		 * a very small time, rather than being masked and replayed).
-		 */
-		if (irqs_enabled) {
-			local_irq_enable();
-			local_irq_disable();
-		} else {
-			replay_soft_interrupts();
-		}
-
 		return false;
 	}
 	local_paca->irq_happened = 0;
@@ -192,6 +174,37 @@ static notrace inline bool prep_irq_for_enabled_exit(bool clear_ri, bool irqs_en
 	return true;
 }
 
+static notrace inline bool prep_irq_for_enabled_exit(bool clear_ri, bool irqs_enabled)
+{
+	if (__prep_irq_for_enabled_exit(clear_ri))
+		return true;
+
+	/*
+	 * Must replay pending soft-masked interrupts now. Don't just
+	 * local_irq_enabe(); local_irq_disable(); because if we are
+	 * returning from an asynchronous interrupt here, another one
+	 * might hit after irqs are enabled, and it would exit via this
+	 * same path allowing another to fire, and so on unbounded.
+	 *
+	 * If interrupts were enabled when this interrupt exited,
+	 * indicating a process context (synchronous) interrupt,
+	 * local_irq_enable/disable can be used, which will enable
+	 * interrupts rather than keeping them masked (unclear how
+	 * much benefit this is over just replaying for all cases,
+	 * because we immediately disable again, so all we're really
+	 * doing is allowing hard interrupts to execute directly for
+	 * a very small time, rather than being masked and replayed).
+	 */
+	if (irqs_enabled) {
+		local_irq_enable();
+		local_irq_disable();
+	} else {
+		replay_soft_interrupts();
+	}
+
+	return false;
+}
+
 /*
  * This should be called after a syscall returns, with r3 the return value
  * from the syscall. If this function returns non-zero, the system call
@@ -209,6 +222,8 @@ 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;
@@ -240,9 +255,9 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 		ret |= _TIF_RESTOREALL;
 	}
 
+again:
 	local_irq_disable();
 
-again:
 	ti_flags = READ_ONCE(*ti_flagsp);
 	while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
 		local_irq_enable();
@@ -286,9 +301,14 @@ 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, true)))
+	if (unlikely(!__prep_irq_for_enabled_exit(!scv))) {
+		user_exit_irqoff();
+		local_irq_enable();
 		goto again;
+	}
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 	local_paca->tm_scratch = regs->msr;