Commit 466e4d80 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Peter Zijlstra
Browse files

task_work: Add TWA_NMI_CURRENT as an additional notify mode. 



Adding task_work from NMI context requires the following:
- The kasan_record_aux_stack() is not NMU safe and must be avoided.
- Using TWA_RESUME is NMI safe. If the NMI occurs while the CPU is in
  userland then it will continue in userland and not invoke the `work'
  callback.

Add TWA_NMI_CURRENT as an additional notify mode. In this mode skip
kasan and use irq_work in hardirq-mode to for needed interrupt. Set
TIF_NOTIFY_RESUME within the irq_work callback due to k[ac]san
instrumentation in test_and_set_bit() which does not look NMI safe in
case of a report.

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240704170424.1466941-3-bigeasy@linutronix.de
parent 058244c6

include/linux/task_work.h

+1 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ enum task_work_notify_mode { 
	TWA_RESUME,

	TWA_SIGNAL,

	TWA_SIGNAL_NO_IPI,

	TWA_NMI_CURRENT,

};



static inline bool task_work_pending(struct task_struct *task)

kernel/task_work.c

+21 −3
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include <linux/irq_work.h>

#include <linux/spinlock.h>

#include <linux/task_work.h>

#include <linux/resume_user_mode.h>



static struct callback_head work_exited; /* all we need is ->next == NULL */



static void task_work_set_notify_irq(struct irq_work *entry)

{

	test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);

}

static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =

	IRQ_WORK_INIT_HARD(task_work_set_notify_irq);



/**

 * task_work_add - ask the @task to execute @work->func()

 * @task: the task which should run the callback
@@ -12,7 +20,7 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */ 
 * @notify: how to notify the targeted task

 *

 * Queue @work for task_work_run() below and notify the @task if @notify

 * is @TWA_RESUME, @TWA_SIGNAL, or @TWA_SIGNAL_NO_IPI.

 * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT.

 *

 * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted

 * task and run the task_work, regardless of whether the task is currently
@@ -24,6 +32,8 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */ 
 * kernel anyway.

 * @TWA_RESUME work is run only when the task exits the kernel and returns to

 * user mode, or before entering guest mode.

 * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the

 * current @task and if the current context is NMI.

 *

 * Fails if the @task is exiting/exited and thus it can't process this @work.

 * Otherwise @work->func() will be called when the @task goes through one of
@@ -44,8 +54,13 @@ int task_work_add(struct task_struct *task, struct callback_head *work, 
{

	struct callback_head *head;



	if (notify == TWA_NMI_CURRENT) {

		if (WARN_ON_ONCE(task != current))

			return -EINVAL;

	} else {

		/* record the work call stack in order to print it in KASAN reports */

		kasan_record_aux_stack(work);

	}



	head = READ_ONCE(task->task_works);

	do {
@@ -66,6 +81,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work, 
	case TWA_SIGNAL_NO_IPI:

		__set_notify_signal(task);

		break;

	case TWA_NMI_CURRENT:

		irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));

		break;

	default:

		WARN_ON_ONCE(1);

		break;