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From: Peter Zijlstra <peterz@infradead.org>
To: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
	mbenes@suse.cz, pmladek@suse.com, mingo@kernel.org
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	joe.lawrence@redhat.com, fweisbec@gmail.com, tglx@linutronix.de,
	hca@linux.ibm.com, svens@linux.ibm.com, sumanthk@linux.ibm.com,
	live-patching@vger.kernel.org, paulmck@kernel.org,
	rostedt@goodmis.org, x86@kernel.org
Subject: [RFC][PATCH v2 09/11] context_tracking,livepatch: Dont disturb NOHZ_FULL
Date: Wed, 29 Sep 2021 17:17:32 +0200	[thread overview]
Message-ID: <20210929152429.067060646@infradead.org> (raw)
In-Reply-To: <20210929151723.162004989@infradead.org>

Using the new context_tracking infrastructure, avoid disturbing
userspace tasks when context tracking is enabled.

When context_tracking_set_cpu_work() returns true, we have the
guarantee that klp_update_patch_state() is called from noinstr code
before it runs normal kernel code. This covers
syscall/exceptions/interrupts and NMI entry.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/context_tracking.h |    2 +-
 include/linux/livepatch.h        |    2 ++
 kernel/context_tracking.c        |   11 +++++------
 kernel/livepatch/transition.c    |   29 ++++++++++++++++++++++++++---
 4 files changed, 34 insertions(+), 10 deletions(-)

--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -10,7 +10,7 @@
 #include <asm/ptrace.h>
 
 enum ct_work {
-	CT_WORK_n = 0,
+	CT_WORK_KLP = 1,
 };
 
 /*
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -201,6 +201,7 @@ void klp_module_going(struct module *mod
 
 void klp_copy_process(struct task_struct *child);
 void klp_update_patch_state(struct task_struct *task);
+void __klp_update_patch_state(struct task_struct *task);
 
 static inline bool klp_patch_pending(struct task_struct *task)
 {
@@ -242,6 +243,7 @@ static inline int klp_module_coming(stru
 static inline void klp_module_going(struct module *mod) {}
 static inline bool klp_patch_pending(struct task_struct *task) { return false; }
 static inline void klp_update_patch_state(struct task_struct *task) {}
+static inline void __klp_update_patch_state(struct task_struct *task) {}
 static inline void klp_copy_process(struct task_struct *child) {}
 
 static inline
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -21,6 +21,7 @@
 #include <linux/hardirq.h>
 #include <linux/export.h>
 #include <linux/kprobes.h>
+#include <linux/livepatch.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/context_tracking.h>
@@ -55,15 +56,13 @@ static noinstr void ct_exit_user_work(struct
 {
 	unsigned int work = arch_atomic_read(&ct->work);
 
-#if 0
-	if (work & CT_WORK_n) {
+	if (work & CT_WORK_KLP) {
 		/* NMI happens here and must still do/finish CT_WORK_n */
-		do_work_n();
+		__klp_update_patch_state(current);
 
 		smp_mb__before_atomic();
-		arch_atomic_andnot(CT_WORK_n, &ct->work);
+		arch_atomic_andnot(CT_WORK_KLP, &ct->work);
 	}
-#endif
 
 	smp_mb__before_atomic();
 	arch_atomic_andnot(CT_SEQ_WORK, &ct->seq);
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -10,6 +10,7 @@
 #include <linux/cpu.h>
 #include <linux/stacktrace.h>
 #include <linux/tracehook.h>
+#include <linux/context_tracking.h>
 #include "core.h"
 #include "patch.h"
 #include "transition.h"
@@ -153,6 +154,11 @@ void klp_cancel_transition(void)
 	klp_complete_transition();
 }
 
+noinstr void __klp_update_patch_state(struct task_struct *task)
+{
+	task->patch_state = READ_ONCE(klp_target_state);
+}
+
 /*
  * Switch the patched state of the task to the set of functions in the target
  * patch state.
@@ -180,8 +186,10 @@ void klp_update_patch_state(struct task_
 	 *    of func->transition, if klp_ftrace_handler() is called later on
 	 *    the same CPU.  See __klp_disable_patch().
 	 */
-	if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
+	if (test_tsk_thread_flag(task, TIF_PATCH_PENDING)) {
 		task->patch_state = READ_ONCE(klp_target_state);
+		clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	}
 
 	preempt_enable_notrace();
 }
@@ -270,15 +278,30 @@ static int klp_check_and_switch_task(str
 {
 	int ret;
 
-	if (task_curr(task))
+	if (task_curr(task)) {
+		/*
+		 * This only succeeds when the task is in NOHZ_FULL user
+		 * mode, the true return value guarantees any kernel entry
+		 * will call klp_update_patch_state().
+		 *
+		 * XXX: ideally we'd simply return 0 here and leave
+		 * TIF_PATCH_PENDING alone, to be fixed up by
+		 * klp_update_patch_state(), except livepatching goes wobbly
+		 * with 'pending' TIF bits on.
+		 */
+		if (context_tracking_set_cpu_work(task_cpu(task), CT_WORK_KLP))
+			goto clear;
+
 		return -EBUSY;
+	}
 
 	ret = klp_check_stack(task, arg);
 	if (ret)
 		return ret;
 
-	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	task->patch_state = klp_target_state;
+clear:
+	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	return 0;
 }
 



  parent reply	other threads:[~2021-09-29 15:58 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29 15:17 [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 01/11] sched: Improve try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 02/11] sched,rcu: Rework try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 03/11] sched,livepatch: Use task_call_func() Peter Zijlstra
2021-10-05 11:40   ` Petr Mladek
2021-10-05 14:03     ` Peter Zijlstra
2021-10-06  8:59   ` Miroslav Benes
2021-09-29 15:17 ` [PATCH v2 04/11] sched: Simplify wake_up_*idle*() Peter Zijlstra
2021-10-13 14:32   ` Qian Cai
2021-10-19  3:47     ` Qian Cai
2021-10-19  8:56       ` Peter Zijlstra
2021-10-19  9:10         ` Peter Zijlstra
2021-10-19 15:32           ` Qian Cai
2021-10-19 15:50             ` Peter Zijlstra
2021-10-19 19:22               ` Qian Cai
2021-10-19 20:27                 ` Peter Zijlstra
     [not found]   ` <CGME20211022134630eucas1p2e79e2816587d182c580459d567c1f2a9@eucas1p2.samsung.com>
2021-10-22 13:46     ` Marek Szyprowski
2021-09-29 15:17 ` [PATCH v2 05/11] sched,livepatch: Use wake_up_if_idle() Peter Zijlstra
2021-10-05 12:00   ` Petr Mladek
2021-10-06  9:16   ` Miroslav Benes
2021-10-07  9:18     ` Vasily Gorbik
2021-10-07 10:02       ` Peter Zijlstra
2021-10-13 19:37   ` Arnd Bergmann
2021-10-14 10:42     ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 06/11] context_tracking: Prefix user_{enter,exit}*() Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 07/11] context_tracking: Add an atomic sequence/state count Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 08/11] context_tracking,rcu: Replace RCU dynticks counter with context_tracking Peter Zijlstra
2021-09-29 18:37   ` Paul E. McKenney
2021-09-29 19:09     ` Peter Zijlstra
2021-09-29 19:11     ` Peter Zijlstra
2021-09-29 19:13     ` Peter Zijlstra
2021-09-29 19:24       ` Peter Zijlstra
2021-09-29 19:45         ` Paul E. McKenney
2021-09-29 18:54   ` Peter Zijlstra
2021-09-29 15:17 ` Peter Zijlstra [this message]
2021-10-06  8:12   ` [RFC][PATCH v2 09/11] context_tracking,livepatch: Dont disturb NOHZ_FULL Petr Mladek
2021-10-06  9:04     ` Peter Zijlstra
2021-10-06 10:29       ` Petr Mladek
2021-10-06 11:41         ` Peter Zijlstra
2021-10-06 11:48         ` Miroslav Benes
2021-09-29 15:17 ` [RFC][PATCH v2 10/11] livepatch: Remove klp_synchronize_transition() Peter Zijlstra
2021-10-06 12:30   ` Petr Mladek
2021-09-29 15:17 ` [RFC][PATCH v2 11/11] context_tracking,x86: Fix text_poke_sync() vs NOHZ_FULL Peter Zijlstra
2021-10-21 18:39   ` Marcelo Tosatti
2021-10-21 18:40     ` Marcelo Tosatti
2021-10-21 19:25     ` Peter Zijlstra
2021-10-21 19:57       ` Marcelo Tosatti
2021-10-21 20:18         ` Peter Zijlstra
2021-10-26 18:19           ` Marcelo Tosatti
2021-10-26 19:38             ` Peter Zijlstra
2021-09-29 18:03 ` [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Paul E. McKenney

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