Message-ID: <20220127173206.358254456@fedora.localdomain>
Date:   Thu, 27 Jan 2022 14:30:38 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Nitesh Lal <nilal@...hat.com>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alex Belits <abelits@...its.com>, Peter Xu <peterx@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: [patch v10 01/10] add basic task isolation prctl interface

Add basic prctl task isolation interface, which allows
informing the kernel that application is executing 
latency sensitive code (where interruptions are undesired).

Interface is described by task_isolation.rst (added by
next patch).

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

---
v6:
 - Move oneshot mode enablement to configuration time (Frederic Weisbecker).
 - Allow more extensions to CFG_SET of ISOL_F_QUIESCE (Frederic Weisbecker).
 - prctl_task_isolation_activate_get should copy active_mask 
   to address in arg2.
v5:
 - No changes
v4:
 - Switch to structures for parameters when possible
   (which are more extensible).
 - Switch to CFG_{S,G}ET naming and drop
   "internal configuration" prctls            (Frederic Weisbecker).

v3:
 - Split in smaller patches              (Nitesh Lal).
 - Misc cleanups                         (Nitesh Lal).
 - Clarify nohz_full is not a dependency (Nicolas Saenz).
 - Incorrect values for prctl definitions (kernel robot).
 - Save configured state, so applications
   can activate externally configured
   task isolation parameters.
-  Remove "system default" notion (chisol should
   make it obsolete).

v2:
- Finer-grained control of quiescing (Frederic Weisbecker / Nicolas Saenz).
- Avoid potential regressions by allowing applications
  to use ISOL_F_QUIESCE_DEFMASK (whose default value
  is configurable in /sys/).         (Nitesh Lal / Nicolas Saenz).

 include/linux/sched.h          |    5 
 include/linux/task_isolation.h |   91 ++++++++++
 include/uapi/linux/prctl.h     |   43 +++++
 init/init_task.c               |    3 
 kernel/Makefile                |    2 
 kernel/fork.c                  |   22 ++
 kernel/sys.c                   |   16 +
 kernel/task_isolation.c        |  350 +++++++++++++++++++++++++++++++++++++++++
 8 files changed, 530 insertions(+), 2 deletions(-)

Index: linux-2.6/include/uapi/linux/prctl.h
===================================================================
--- linux-2.6.orig/include/uapi/linux/prctl.h
+++ linux-2.6/include/uapi/linux/prctl.h
@@ -275,4 +275,51 @@ struct prctl_mm_map {
 #define PR_SET_VMA		0x53564d41
 # define PR_SET_VMA_ANON_NAME		0
 
+#define PR_ISOL_FEAT_GET		63
+#define PR_ISOL_CFG_GET			64
+#define PR_ISOL_CFG_SET			65
+
+/* arg2 to CFG_GET/CFG_SET */
+# define I_CFG_FEAT			1
+# define I_CFG_INHERIT			2
+
+#define PR_ISOL_ACTIVATE_GET		66
+#define PR_ISOL_ACTIVATE_SET		67
+
+
+/* Supported features */
+# define ISOL_F_QUIESCE			(1UL << 0)
+
+# define ISOL_F_QUIESCE_MULTIPLE	(1UL << 0)
+#  define ISOL_F_QUIESCE_VMSTATS	(1UL << 0)
+
+struct task_isol_quiesce_extensions {
+	__u64 flags;
+	__u64 supported_quiesce_bits;
+	__u64 pad[6];
+};
+
+/*
+ * This structure provides control over
+ * inheritance of task isolation across
+ * clone and fork.
+ */
+struct task_isol_inherit_control {
+	__u8	inherit_mask;
+	__u8	flags;
+	__u8	pad[6];
+};
+
+# define ISOL_INHERIT_CONF		(1UL << 0)
+# define ISOL_INHERIT_ACTIVE		(1UL << 1)
+
+struct task_isol_quiesce_control {
+	__u64 flags;
+	__u64 quiesce_mask;
+	__u64 quiesce_oneshot_mask;
+	__u64 pad[5];
+};
+
+# define QUIESCE_CONTROL		(1UL << 0)
+
 #endif /* _LINUX_PRCTL_H */
Index: linux-2.6/kernel/Makefile
===================================================================
--- linux-2.6.orig/kernel/Makefile
+++ linux-2.6/kernel/Makefile
@@ -132,6 +132,8 @@ obj-$(CONFIG_WATCH_QUEUE) += watch_queue
 obj-$(CONFIG_RESOURCE_KUNIT_TEST) += resource_kunit.o
 obj-$(CONFIG_SYSCTL_KUNIT_TEST) += sysctl-test.o
 
+obj-$(CONFIG_TASK_ISOLATION) += task_isolation.o
+
 CFLAGS_stackleak.o += $(DISABLE_STACKLEAK_PLUGIN)
 obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += stackleak.o
 KASAN_SANITIZE_stackleak.o := n
Index: linux-2.6/kernel/sys.c
===================================================================
--- linux-2.6.orig/kernel/sys.c
+++ linux-2.6/kernel/sys.c
@@ -58,6 +58,7 @@
 #include <linux/sched/coredump.h>
 #include <linux/sched/task.h>
 #include <linux/sched/cputime.h>
+#include <linux/task_isolation.h>
 #include <linux/rcupdate.h>
 #include <linux/uidgid.h>
 #include <linux/cred.h>
@@ -2593,6 +2594,21 @@ SYSCALL_DEFINE5(prctl, int, option, unsi
 	case PR_SET_VMA:
 		error = prctl_set_vma(arg2, arg3, arg4, arg5);
 		break;
+	case PR_ISOL_FEAT_GET:
+		error = prctl_task_isol_feat_get(arg2, arg3, arg4, arg5);
+		break;
+	case PR_ISOL_CFG_GET:
+		error = prctl_task_isol_cfg_get(arg2, arg3, arg4, arg5);
+		break;
+	case PR_ISOL_CFG_SET:
+		error = prctl_task_isol_cfg_set(arg2, arg3, arg4, arg5);
+		break;
+	case PR_ISOL_ACTIVATE_GET:
+		error = prctl_task_isol_activate_get(arg2, arg3, arg4, arg5);
+		break;
+	case PR_ISOL_ACTIVATE_SET:
+		error = prctl_task_isol_activate_set(arg2, arg3, arg4, arg5);
+		break;
 	default:
 		error = -EINVAL;
 		break;
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -67,6 +67,7 @@ struct sighand_struct;
 struct signal_struct;
 struct task_delay_info;
 struct task_group;
+struct task_isol_info;
 
 /*
  * Task state bitmask. NOTE! These bits are also
@@ -1492,6 +1493,10 @@ struct task_struct {
 	struct callback_head		l1d_flush_kill;
 #endif
 
+#ifdef CONFIG_TASK_ISOLATION
+	struct task_isol_info		*task_isol_info;
+#endif
+
 	/*
 	 * New fields for task_struct should be added above here, so that
 	 * they are included in the randomized portion of task_struct.
Index: linux-2.6/init/init_task.c
===================================================================
--- linux-2.6.orig/init/init_task.c
+++ linux-2.6/init/init_task.c
@@ -209,6 +209,9 @@ struct task_struct init_task
 #ifdef CONFIG_SECCOMP_FILTER
 	.seccomp	= { .filter_count = ATOMIC_INIT(0) },
 #endif
+#ifdef CONFIG_TASK_ISOLATION
+	.task_isol_info	= NULL,
+#endif
 };
 EXPORT_SYMBOL(init_task);
 
Index: linux-2.6/kernel/fork.c
===================================================================
--- linux-2.6.orig/kernel/fork.c
+++ linux-2.6/kernel/fork.c
@@ -97,6 +97,7 @@
 #include <linux/scs.h>
 #include <linux/io_uring.h>
 #include <linux/bpf.h>
+#include <linux/task_isolation.h>
 
 #include <asm/pgalloc.h>
 #include <linux/uaccess.h>
@@ -748,6 +749,7 @@ void __put_task_struct(struct task_struc
 	WARN_ON(refcount_read(&tsk->usage));
 	WARN_ON(tsk == current);
 
+	task_isol_free(tsk);
 	io_uring_free(tsk);
 	cgroup_free(tsk);
 	task_numa_free(tsk, true);
@@ -1557,6 +1559,15 @@ out:
 	return error;
 }
 
+static int copy_task_isol(struct task_struct *tsk)
+{
+#ifdef CONFIG_TASK_ISOLATION
+	if (current->task_isol_info)
+		return __copy_task_isol(tsk);
+#endif
+	return 0;
+}
+
 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 {
 	struct sighand_struct *sig;
@@ -2129,7 +2140,9 @@ static __latent_entropy struct task_stru
 	RCU_INIT_POINTER(p->bpf_storage, NULL);
 	p->bpf_ctx = NULL;
 #endif
-
+#ifdef CONFIG_TASK_ISOLATION
+	p->task_isol_info = NULL;
+#endif
 	/* Perform scheduler related setup. Assign this task to a CPU. */
 	retval = sched_fork(clone_flags, p);
 	if (retval)
@@ -2173,6 +2186,9 @@ static __latent_entropy struct task_stru
 	retval = copy_thread(clone_flags, args->stack, args->stack_size, p, args->tls);
 	if (retval)
 		goto bad_fork_cleanup_io;
+	retval = copy_task_isol(p);
+	if (retval)
+		goto bad_fork_cleanup_thread;
 
 	stackleak_task_init(p);
 
@@ -2181,7 +2197,7 @@ static __latent_entropy struct task_stru
 				args->set_tid_size);
 		if (IS_ERR(pid)) {
 			retval = PTR_ERR(pid);
-			goto bad_fork_cleanup_thread;
+			goto bad_fork_cleanup_task_isol;
 		}
 	}
 
@@ -2400,6 +2416,8 @@ bad_fork_put_pidfd:
 bad_fork_free_pid:
 	if (pid != &init_struct_pid)
 		free_pid(pid);
+bad_fork_cleanup_task_isol:
+	task_isol_free(p);
 bad_fork_cleanup_thread:
 	exit_thread(p);
 bad_fork_cleanup_io:
Index: linux-2.6/include/linux/task_isolation.h
===================================================================
--- /dev/null
+++ linux-2.6/include/linux/task_isolation.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __LINUX_TASK_ISOL_H
+#define __LINUX_TASK_ISOL_H
+
+#ifdef CONFIG_TASK_ISOLATION
+
+struct task_isol_info {
+	/* Which features have been configured */
+	u64 conf_mask;
+	/* Which features are active */
+	u64 active_mask;
+	/* Quiesce mask */
+	u64 quiesce_mask;
+
+	/* Oneshot mask */
+	u64 oneshot_mask;
+
+	u8 inherit_mask;
+};
+
+extern void __task_isol_free(struct task_struct *tsk);
+
+static inline void task_isol_free(struct task_struct *tsk)
+{
+	if (tsk->task_isol_info)
+		__task_isol_free(tsk);
+}
+
+int prctl_task_isol_feat_get(unsigned long arg2, unsigned long arg3,
+			     unsigned long arg4, unsigned long arg5);
+int prctl_task_isol_cfg_get(unsigned long arg2, unsigned long arg3,
+			    unsigned long arg4, unsigned long arg5);
+int prctl_task_isol_cfg_set(unsigned long arg2, unsigned long arg3,
+			    unsigned long arg4, unsigned long arg5);
+int prctl_task_isol_activate_get(unsigned long arg2, unsigned long arg3,
+				 unsigned long arg4, unsigned long arg5);
+int prctl_task_isol_activate_set(unsigned long arg2, unsigned long arg3,
+				 unsigned long arg4, unsigned long arg5);
+
+int __copy_task_isol(struct task_struct *tsk);
+
+#else
+
+static inline void task_isol_free(struct task_struct *tsk)
+{
+}
+
+static inline int prctl_task_isol_feat_get(unsigned long arg2,
+					   unsigned long arg3,
+					   unsigned long arg4,
+					   unsigned long arg5)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int prctl_task_isoln_cfg_get(unsigned long arg2,
+					   unsigned long arg3,
+					   unsigned long arg4,
+					   unsigned long arg5)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int prctl_task_isol_cfg_set(unsigned long arg2,
+					  unsigned long arg3,
+					  unsigned long arg4,
+					  unsigned long arg5)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int prctl_task_isol_activate_get(unsigned long arg2,
+					       unsigned long arg3,
+					       unsigned long arg4,
+					       unsigned long arg5)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int prctl_task_isol_activate_set(unsigned long arg2,
+					       unsigned long arg3,
+					       unsigned long arg4,
+					       unsigned long arg5)
+{
+	return -EOPNOTSUPP;
+}
+
+#endif /* CONFIG_TASK_ISOLATION */
+
+#endif /* __LINUX_TASK_ISOL_H */
Index: linux-2.6/kernel/task_isolation.c
===================================================================
--- /dev/null
+++ linux-2.6/kernel/task_isolation.c
@@ -0,0 +1,351 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Implementation of task isolation.
+ *
+ * Authors:
+ *   Chris Metcalf <cmetcalf@...lanox.com>
+ *   Alex Belits <abelits@...its.com>
+ *   Yuri Norov <ynorov@...vell.com>
+ *   Marcelo Tosatti <mtosatti@...hat.com>
+ */
+
+#include <linux/sched.h>
+#include <linux/task_isolation.h>
+#include <linux/prctl.h>
+#include <linux/slab.h>
+#include <linux/kobject.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/init.h>
+#include <linux/sched/task.h>
+
+void __task_isol_free(struct task_struct *tsk)
+{
+	if (!tsk->task_isol_info)
+		return;
+	kfree(tsk->task_isol_info);
+	tsk->task_isol_info = NULL;
+}
+
+static struct task_isol_info *task_isol_alloc_context(void)
+{
+	struct task_isol_info *info;
+
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+	if (unlikely(!info))
+		return ERR_PTR(-ENOMEM);
+
+	return info;
+}
+
+int prctl_task_isol_feat_get(unsigned long arg2, unsigned long arg3,
+				  unsigned long arg4, unsigned long arg5)
+{
+	int ret;
+	void __user *addr = (void __user *) arg3;
+
+	switch (arg2) {
+	case 0: {
+		u64 supported_fmask = ISOL_F_QUIESCE;
+
+		ret = 0;
+		if (copy_to_user(addr, &supported_fmask, sizeof(u64)))
+			ret = -EFAULT;
+
+		return ret;
+	}
+	case ISOL_F_QUIESCE: {
+		struct task_isol_quiesce_extensions *q_ext;
+
+		q_ext = kzalloc(sizeof(struct task_isol_quiesce_extensions),
+			 GFP_KERNEL);
+		if (!q_ext)
+			return -ENOMEM;
+
+		q_ext->supported_quiesce_bits = ISOL_F_QUIESCE_VMSTATS;
+
+		ret = 0;
+		if (copy_to_user(addr, q_ext, sizeof(*q_ext)))
+			ret = -EFAULT;
+		kfree(q_ext);
+		return ret;
+	}
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
+static int cfg_inherit_get(unsigned long arg3, unsigned long arg4,
+			   unsigned long arg5)
+{
+	struct task_isol_inherit_control *i_ctrl;
+	int ret;
+	void __user *addr = (void __user *) arg3;
+
+	if (!current->task_isol_info)
+		return -EINVAL;
+
+	i_ctrl = kzalloc(sizeof(struct task_isol_inherit_control),
+			 GFP_KERNEL);
+	if (!i_ctrl)
+		return -ENOMEM;
+
+	i_ctrl->inherit_mask = current->task_isol_info->inherit_mask;
+
+	ret = 0;
+	if (copy_to_user(addr, i_ctrl, sizeof(*i_ctrl)))
+		ret = -EFAULT;
+	kfree(i_ctrl);
+
+	return ret;
+}
+
+static int cfg_feat_get(unsigned long arg3, unsigned long arg4,
+			unsigned long arg5)
+{
+	int ret = 0;
+
+	switch (arg3) {
+	case 0: {
+		void __user *addr = (void __user *)arg4;
+		u64 cfg_mask = 0;
+
+		if (current->task_isol_info)
+			cfg_mask = current->task_isol_info->conf_mask;
+
+		if (copy_to_user(addr, &cfg_mask, sizeof(u64)))
+			ret = -EFAULT;
+
+		return ret;
+	}
+	case ISOL_F_QUIESCE: {
+		struct task_isol_quiesce_control *i_qctrl;
+		void __user *addr = (void __user *)arg5;
+
+		if (arg4 != QUIESCE_CONTROL)
+			return -EINVAL;
+
+		i_qctrl = kzalloc(sizeof(struct task_isol_quiesce_control),
+				  GFP_KERNEL);
+		if (!i_qctrl)
+			return -ENOMEM;
+
+		if (current->task_isol_info)
+			i_qctrl->quiesce_mask = current->task_isol_info->quiesce_mask;
+
+		if (copy_to_user(addr, i_qctrl, sizeof(*i_qctrl)))
+			ret = -EFAULT;
+
+		kfree(i_qctrl);
+		return ret;
+	}
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
+int prctl_task_isol_cfg_get(unsigned long arg2, unsigned long arg3,
+				 unsigned long arg4, unsigned long arg5)
+{
+	switch (arg2) {
+	case I_CFG_FEAT:
+		return cfg_feat_get(arg3, arg4, arg5);
+	case I_CFG_INHERIT:
+		return cfg_inherit_get(arg3, arg4, arg5);
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
+static int cfg_inherit_set(unsigned long arg3, unsigned long arg4,
+			   unsigned long arg5)
+{
+	int ret = 0;
+	struct task_isol_inherit_control *i_ctrl;
+	const void __user *addr = (const void __user *)arg3;
+
+	i_ctrl = kzalloc(sizeof(struct task_isol_inherit_control),
+			 GFP_KERNEL);
+	if (!i_ctrl)
+		return -ENOMEM;
+
+	ret = -EFAULT;
+	if (copy_from_user(i_ctrl, addr, sizeof(*i_ctrl)))
+		goto out_free;
+
+	ret = -EINVAL;
+	if (i_ctrl->inherit_mask & ~(ISOL_INHERIT_CONF|ISOL_INHERIT_ACTIVE))
+		goto out_free;
+
+	if (i_ctrl->inherit_mask & ISOL_INHERIT_ACTIVE)
+		if (!(i_ctrl->inherit_mask & ISOL_INHERIT_CONF))
+			goto out_free;
+
+	if (!current->task_isol_info) {
+		struct task_isol_info *task_isol_info;
+
+		task_isol_info = task_isol_alloc_context();
+		if (IS_ERR(task_isol_info)) {
+			ret = PTR_ERR(task_isol_info);
+			goto out_free;
+		}
+		current->task_isol_info = task_isol_info;
+	}
+
+	ret = 0;
+	current->task_isol_info->inherit_mask = i_ctrl->inherit_mask;
+
+out_free:
+	kfree(i_ctrl);
+
+	return ret;
+}
+
+static int cfg_feat_quiesce_set(unsigned long arg4, unsigned long arg5)
+{
+	struct task_isol_info *task_isol_info;
+	struct task_isol_quiesce_control *i_qctrl;
+	int ret = 0;
+	const void __user *addr = (const void __user *)arg5;
+
+	if (arg4 != QUIESCE_CONTROL)
+		return -EINVAL;
+
+	i_qctrl = kzalloc(sizeof(struct task_isol_quiesce_control),
+			 GFP_KERNEL);
+	if (!i_qctrl)
+		return -ENOMEM;
+
+	ret = -EFAULT;
+	if (copy_from_user(i_qctrl, addr, sizeof(*i_qctrl)))
+		goto out_free;
+
+	ret = -EINVAL;
+	if (i_qctrl->flags != 0)
+		goto out_free;
+
+	if (i_qctrl->quiesce_mask != ISOL_F_QUIESCE_VMSTATS &&
+	    i_qctrl->quiesce_mask != 0)
+		goto out_free;
+
+	if ((~i_qctrl->quiesce_mask & i_qctrl->quiesce_oneshot_mask) != 0)
+		goto out_free;
+
+	/* current->task_isol_info is only allocated/freed from task
+	 * context.
+	 */
+	if (!current->task_isol_info) {
+		task_isol_info = task_isol_alloc_context();
+		if (IS_ERR(task_isol_info)) {
+			ret = PTR_ERR(task_isol_info);
+			goto out_free;
+		}
+		current->task_isol_info = task_isol_info;
+	}
+
+	task_isol_info = current->task_isol_info;
+
+	task_isol_info->quiesce_mask = i_qctrl->quiesce_mask;
+	task_isol_info->oneshot_mask = i_qctrl->quiesce_oneshot_mask;
+	task_isol_info->conf_mask |= ISOL_F_QUIESCE;
+	ret = 0;
+
+out_free:
+	kfree(i_qctrl);
+
+	return ret;
+}
+
+int prctl_task_isol_cfg_set(unsigned long arg2, unsigned long arg3,
+				 unsigned long arg4, unsigned long arg5)
+{
+	switch (arg2) {
+	case I_CFG_FEAT:
+		switch (arg3) {
+		case ISOL_F_QUIESCE:
+			return cfg_feat_quiesce_set(arg4, arg5);
+		default:
+			break;
+		}
+		break;
+	case I_CFG_INHERIT:
+		return cfg_inherit_set(arg3, arg4, arg5);
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
+int __copy_task_isol(struct task_struct *tsk)
+{
+	struct task_isol_info *info, *new_info;
+
+	info = current->task_isol_info;
+	if (!(info->inherit_mask & (ISOL_INHERIT_CONF|ISOL_INHERIT_ACTIVE)))
+		return 0;
+
+	new_info = task_isol_alloc_context();
+	if (IS_ERR(new_info))
+		return PTR_ERR(new_info);
+
+	new_info->inherit_mask = info->inherit_mask;
+
+	if (info->inherit_mask & ISOL_INHERIT_CONF) {
+		new_info->quiesce_mask = info->quiesce_mask;
+		new_info->conf_mask = info->conf_mask;
+		new_info->oneshot_mask = info->oneshot_mask;
+	}
+
+	if (info->inherit_mask & ISOL_INHERIT_ACTIVE)
+		new_info->active_mask = info->active_mask;
+
+	tsk->task_isol_info = new_info;
+
+	return 0;
+}
+
+int prctl_task_isol_activate_set(unsigned long arg2, unsigned long arg3,
+				      unsigned long arg4, unsigned long arg5)
+{
+	int ret;
+	struct task_isol_info *task_isol_info;
+	u64 active_mask;
+	const void __user *addr_mask = (const void __user *)arg2;
+
+	ret = -EFAULT;
+	if (copy_from_user(&active_mask, addr_mask, sizeof(u64)))
+		goto out;
+
+	ret = -EINVAL;
+	if (active_mask != ISOL_F_QUIESCE && active_mask != 0)
+		return ret;
+
+	task_isol_info = current->task_isol_info;
+	if (!task_isol_info)
+		return ret;
+
+	task_isol_info->active_mask = active_mask;
+	ret = 0;
+
+out:
+	return ret;
+}
+
+int prctl_task_isol_activate_get(unsigned long arg2, unsigned long arg3,
+				      unsigned long arg4, unsigned long arg5)
+{
+	struct task_isol_info *task_isol_info;
+	void __user *addr_mask = (void __user *)arg2;
+
+	task_isol_info = current->task_isol_info;
+	if (!task_isol_info)
+		return -EINVAL;
+
+	if (copy_to_user(addr_mask, &task_isol_info->active_mask, sizeof(u64)))
+		return -EFAULT;
+
+	return 0;
+}
Index: linux-2.6/init/Kconfig
===================================================================
--- linux-2.6.orig/init/Kconfig
+++ linux-2.6/init/Kconfig
@@ -675,6 +675,22 @@ config CPU_ISOLATION
 
 	  Say Y if unsure.
 
+config TASK_ISOLATION
+	bool "Task isolation prctl()"
+	depends on GENERIC_ENTRY
+	default n
+	help
+	  Certain types of applications benefit from running uninterrupted by
+	  background OS activities. Realtime systems and high-bandwidth networking
+	  applications with user-space drivers can fall into the category.
+
+	  To create an OS noise free environment for the application, this option
+	  enables the task isolation prctl interface, which allows userspace to
+	  inform the kernel the start and end of the latency sensitive application
+	  section (with configurable system behaviour for that section).
+
+	  Say N if unsure.
+
 source "kernel/rcu/Kconfig"
 
 config BUILD_BIN2C

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