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task_work: Add TWA_NMI_CURRENT as an additional notify mode.

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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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240704170424.1466941-3-bigeasy@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2024-07-04 19:03:36 +02:00 committed by Peter Zijlstra
parent 058244c683
commit 466e4d801c
2 changed files with 22 additions and 3 deletions
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1
include/linux/task_work.h
View File

@ -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)

20
kernel/task_work.c
View File

@ -1,10 +1,18 @@
// 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;