[PATCH v7 30/42] powerpc/64: context tracking remove _TIF_NOHZ
Nicholas Piggin
npiggin at gmail.com
Sun Jan 31 00:08:40 AEDT 2021
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 at 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 | 72 ++++++++++++++++----------
5 files changed, 47 insertions(+), 38 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 316c3ba16554..45c4420fe339 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))
@@ -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;
--
2.23.0
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