[PATCH v11 00/13] support "task_isolation" mode

[PATCH v11 00/13] support "task_isolation" mode

[Chris Metcalf]

Here is a respin of the task-isolation patch set, folding in
comments from Frederic Weisbecker, Will Deacon, Andy Lutomirski,
Kees Cook and others.

Changes since v10:

- In the API, I added a new PR_TASK_ISOLATION_ONE_SHOT flag to
  implement the semantics that Frederic had requested.  It remains to
  be seen whether it makes sense to: leave this as a dynamic flag; back
  out the change and remove the flag and leave the semantics always
  "persistent" (as before); or remove the flag and make the semantics
  always one-shot.  I tend to favor removing the flag and keeping the
  semantics persistent, but having it as a flag provides a specific
  implementation to let us think about the tradeoffs.

- I added a TIF_TASK_ISOLATION flag to clarify and simplify the tests for
  whether task isolation is currently enabled.  We remove the previous
  inline wrappers for task_isolation_ready/enter() and just call the
  real functions unconditionally if TIF_TASK_ISOLATION is set, and
  similarly simplify the task_isolation_syscall/exception() helpers.

- I added a task_isolation_set_flags() helper to set or clear
  TIF_TASK_ISOLATION as needed; it also allows me to get rid of the
  #ifdefs in signal.c and fork.c, which is a nice plus.

- The initial prctl() to enable task isolation now also checks
  can_stop_full_tick() to look for additional potential problems when
  starting up task isolation (other schedulable tasks or POSIX cpu
  timers being the two most obvious examples).  The function is now no
  longer static in kernel/time/tick-sched.c.

- I expanded the existing comment justifying calling
  set_tsk_need_resched() if dynticks are still running when a task
  isolation task wants to enter userspace.  As mentioned in my reply
  to Frederic, I still consider it an open question whether we should
  do some form of struct notification type work here, but on balance I
  think it's overcomplicated to do so.

- We now make sure to clear task isolation when delivering a signal,
  since by definition signals pretty much mean you've lost task
  isolation, it's a well-defined semantic to provide to userspace, and
  it means we can always deliver the signal for STRICT mode saying we
  were interrupted.  Also, doing this is necessary to catch more of the
  cases where we clear task isolation mode for the new ONE_SHOT mode.

- For STRICT mode, I moved the setting of the attempted syscall's return
  value to the generic code via the syscall_set_return_value()
  function.  I also restructured the code slightly to make it
  easier to add ONE_SHOT support in a following patch.  On Kees Cook's
  advice I continue to just support the simple TIF_TASK_ISOLATION check
  in syscall entry that calls out to a few lines of C code, but there is
  an ongoing conversation with Andy Lutomirski about using a proposed
  seccomp() extension to guard syscall entry instead.

- The arch/arm64 patch to factor the work_pending state machine into C was
  updated to include the arch/arm call to trace_hardirqs_off() at the
  top.  Will Deacon noticed that we were missing this support.  I also
  restructured the loop as a do/while at his suggestion, rather than
  copying the x86 while(true)/break idiom.

- Changed the S-O-B lines from ezchip.com to mellanox.com.

The previous (v10) patch series is here:

https://lkml.kernel.org/r/1456949376-4910-1-git-send-email-cmetcalf@ezchip.com

This version of the patch series has been tested on arm64 and tile,
and build-tested on x86.

It remains true that the 1 Hz tick needs to be disabled for this
patch series to be able to achieve its primary goal of enabling
truly tick-free operation, but that is ongoing orthogonal work.

The series is available at:

  git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile.git dataplane

Chris Metcalf (13):
  vmstat: add quiet_vmstat_sync function
  vmstat: add vmstat_idle function
  lru_add_drain_all: factor out lru_add_drain_needed
  task_isolation: add initial support
  task_isolation: support CONFIG_TASK_ISOLATION_ALL
  task_isolation: support PR_TASK_ISOLATION_STRICT mode
  task_isolation: add debug boot flag
  task_isolation: add PR_TASK_ISOLATION_ONE_SHOT flag
  arm, tile: turn off timer tick for oneshot_stopped state
  arch/x86: enable task isolation functionality
  arch/tile: enable task isolation functionality
  arm64: factor work_pending state machine to C
  arch/arm64: enable task isolation functionality

 Documentation/kernel-parameters.txt    |  16 ++
 arch/arm64/include/asm/thread_info.h   |   5 +-
 arch/arm64/kernel/entry.S              |  12 +-
 arch/arm64/kernel/ptrace.c             |  15 +-
 arch/arm64/kernel/signal.c             |  42 ++++-
 arch/arm64/kernel/smp.c                |   2 +
 arch/arm64/mm/fault.c                  |   4 +
 arch/tile/include/asm/thread_info.h    |   4 +-
 arch/tile/kernel/process.c             |   9 +
 arch/tile/kernel/ptrace.c              |   7 +
 arch/tile/kernel/single_step.c         |   5 +
 arch/tile/kernel/smp.c                 |  28 +--
 arch/tile/kernel/time.c                |   1 +
 arch/tile/kernel/unaligned.c           |   3 +
 arch/tile/mm/fault.c                   |   3 +
 arch/tile/mm/homecache.c               |   2 +
 arch/x86/entry/common.c                |  18 +-
 arch/x86/include/asm/thread_info.h     |   2 +
 arch/x86/kernel/traps.c                |   2 +
 arch/x86/mm/fault.c                    |   2 +
 drivers/base/cpu.c                     |  18 ++
 drivers/clocksource/arm_arch_timer.c   |   2 +
 include/linux/context_tracking_state.h |   6 +
 include/linux/isolation.h              |  63 +++++++
 include/linux/sched.h                  |   3 +
 include/linux/swap.h                   |   1 +
 include/linux/tick.h                   |   2 +
 include/linux/vmstat.h                 |   4 +
 include/uapi/linux/prctl.h             |   9 +
 init/Kconfig                           |  30 ++++
 kernel/Makefile                        |   1 +
 kernel/fork.c                          |   3 +
 kernel/irq_work.c                      |   5 +-
 kernel/isolation.c                     | 313 +++++++++++++++++++++++++++++++++
 kernel/sched/core.c                    |  18 ++
 kernel/signal.c                        |   8 +
 kernel/smp.c                           |   6 +-
 kernel/softirq.c                       |  33 ++++
 kernel/sys.c                           |   9 +
 kernel/time/tick-sched.c               |  33 ++--
 mm/swap.c                              |  15 +-
 mm/vmstat.c                            |  21 +++
 42 files changed, 730 insertions(+), 55 deletions(-)
 create mode 100644 include/linux/isolation.h
 create mode 100644 kernel/isolation.c

-- 
2.7.2

[PATCH v11 01/13] vmstat: add quiet_vmstat_sync function

[Chris Metcalf]

In commit f01f17d3705b ("mm, vmstat: make quiet_vmstat lighter")
the quiet_vmstat() function became asynchronous, in the sense that
the vmstat work was still scheduled to run on the core when the
function returned.  For task isolation, we need a synchronous
version of the function that guarantees that the vmstat worker
will not run on the core on return from the function.  Add a
quiet_vmstat_sync() function with that semantic.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 include/linux/vmstat.h | 2 ++
 mm/vmstat.c            | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 73fae8c4a5fb..43b2f1c33266 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -190,6 +190,7 @@ extern void dec_zone_state(struct zone *, enum zone_stat_item);
 extern void __dec_zone_state(struct zone *, enum zone_stat_item);
 
 void quiet_vmstat(void);
+void quiet_vmstat_sync(void);
 void cpu_vm_stats_fold(int cpu);
 void refresh_zone_stat_thresholds(void);
 
@@ -251,6 +252,7 @@ static inline void __dec_zone_page_state(struct page *page,
 static inline void refresh_zone_stat_thresholds(void) { }
 static inline void cpu_vm_stats_fold(int cpu) { }
 static inline void quiet_vmstat(void) { }
+static inline void quiet_vmstat_sync(void) { }
 
 static inline void drain_zonestat(struct zone *zone,
 			struct per_cpu_pageset *pset) { }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 084c6725b373..ff569246fcb5 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1469,6 +1469,15 @@ void quiet_vmstat(void)
 	refresh_cpu_vm_stats(false);
 }
 
+/*
+ * Synchronously quiet vmstat so the work is guaranteed not to run on return.
+ */
+void quiet_vmstat_sync(void)
+{
+	cpumask_set_cpu(smp_processor_id(), cpu_stat_off);
+	cancel_delayed_work_sync(this_cpu_ptr(&vmstat_work));
+	refresh_cpu_vm_stats(false);
+}
 
 /*
  * Shepherd worker thread that checks the
-- 
2.7.2

[PATCH v11 02/13] vmstat: add vmstat_idle function

[Chris Metcalf]

This function checks to see if a vmstat worker is not running,
and the vmstat diffs don't require an update.  The function is
called from the task-isolation code to see if we need to
actually do some work to quiet vmstat.

Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 include/linux/vmstat.h |  2 ++
 mm/vmstat.c            | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 43b2f1c33266..504ebd1fdf33 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -191,6 +191,7 @@ extern void __dec_zone_state(struct zone *, enum zone_stat_item);
 
 void quiet_vmstat(void);
 void quiet_vmstat_sync(void);
+bool vmstat_idle(void);
 void cpu_vm_stats_fold(int cpu);
 void refresh_zone_stat_thresholds(void);
 
@@ -253,6 +254,7 @@ static inline void refresh_zone_stat_thresholds(void) { }
 static inline void cpu_vm_stats_fold(int cpu) { }
 static inline void quiet_vmstat(void) { }
 static inline void quiet_vmstat_sync(void) { }
+static inline bool vmstat_idle(void) { return true; }
 
 static inline void drain_zonestat(struct zone *zone,
 			struct per_cpu_pageset *pset) { }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index ff569246fcb5..3840c42f029d 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1480,6 +1480,18 @@ void quiet_vmstat_sync(void)
 }
 
 /*
+ * Report on whether vmstat processing is quiesced on the core currently:
+ * no vmstat worker running and no vmstat updates to perform.
+ */
+bool vmstat_idle(void)
+{
+	int cpu = smp_processor_id();
+	return cpumask_test_cpu(cpu, cpu_stat_off) &&
+		!delayed_work_pending(this_cpu_ptr(&vmstat_work)) &&
+		!need_update(cpu);
+}
+
+/*
  * Shepherd worker thread that checks the
  * differentials of processors that have their worker
  * threads for vm statistics updates disabled because of
-- 
2.7.2

[PATCH v11 03/13] lru_add_drain_all: factor out lru_add_drain_needed

[Chris Metcalf]

This per-cpu check was being done in the loop in lru_add_drain_all(),
but having it be callable for a particular cpu is helpful for the
task-isolation patches.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 include/linux/swap.h |  1 +
 mm/swap.c            | 15 ++++++++++-----
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index d18b65c53dbb..da21f5240702 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -304,6 +304,7 @@ extern void activate_page(struct page *);
 extern void mark_page_accessed(struct page *);
 extern void lru_add_drain(void);
 extern void lru_add_drain_cpu(int cpu);
+extern bool lru_add_drain_needed(int cpu);
 extern void lru_add_drain_all(void);
 extern void rotate_reclaimable_page(struct page *page);
 extern void deactivate_file_page(struct page *page);
diff --git a/mm/swap.c b/mm/swap.c
index 09fe5e97714a..bdcdfa21094c 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -653,6 +653,15 @@ void deactivate_page(struct page *page)
 	}
 }
 
+bool lru_add_drain_needed(int cpu)
+{
+	return (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
+		pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||
+		pagevec_count(&per_cpu(lru_deactivate_file_pvecs, cpu)) ||
+		pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
+		need_activate_page_drain(cpu));
+}
+
 void lru_add_drain(void)
 {
 	lru_add_drain_cpu(get_cpu());
@@ -679,11 +688,7 @@ void lru_add_drain_all(void)
 	for_each_online_cpu(cpu) {
 		struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
 
-		if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
-		    pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||
-		    pagevec_count(&per_cpu(lru_deactivate_file_pvecs, cpu)) ||
-		    pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
-		    need_activate_page_drain(cpu)) {
+		if (lru_add_drain_needed(cpu)) {
 			INIT_WORK(work, lru_add_drain_per_cpu);
 			schedule_work_on(cpu, work);
 			cpumask_set_cpu(cpu, &has_work);
-- 
2.7.2

[PATCH v11 04/13] task_isolation: add initial support

[Chris Metcalf]

The existing nohz_full mode is designed as a "soft" isolation mode
that makes tradeoffs to minimize userspace interruptions while
still attempting to avoid overheads in the kernel entry/exit path,
to provide 100% kernel semantics, etc.

However, some applications require a "hard" commitment from the
kernel to avoid interruptions, in particular userspace device driver
style applications, such as high-speed networking code.

This change introduces a framework to allow applications
to elect to have the "hard" semantics as needed, specifying
prctl(PR_SET_TASK_ISOLATION, PR_TASK_ISOLATION_ENABLE) to do so.
Subsequent commits will add additional flags and additional
semantics.

The kernel must be built with the new TASK_ISOLATION Kconfig flag
to enable this mode, and the kernel booted with an appropriate
task_isolation=CPULIST boot argument, which enables nohz_full and
isolcpus as well.  The "task_isolation" state is then indicated by
setting a new task struct field, task_isolation_flag, to the value
passed by prctl(), and also setting a TIF_TASK_ISOLATION bit in
thread_info flags.  When task isolation is enabled for a task, and it
is returning to userspace on a task isolation core, it calls the
new task_isolation_ready() / task_isolation_enter() routines to
take additional actions to help the task avoid being interrupted
in the future.

A new /sys/devices/system/cpu/task_isolation pseudo-file is added,
parallel to the comparable nohz_full file.

The task_isolation_ready() call is invoked when TIF_TASK_ISOLATION is
set in prepare_exit_to_usermode() or its architectural equivalent,
and forces the loop to retry if the system is not ready.  It is
called with interrupts disabled and inspects the kernel state
to determine if it is safe to return into an isolated state.
In particular, if it sees that the scheduler tick is still enabled,
it reports that it is not yet safe.

Each time through the loop of TIF work to do, if TIF_TASK_ISOLATION
is set, we call the new task_isolation_enter() routine.  This
takes any actions that might avoid a future interrupt to the core,
such as a worker thread being scheduled that could be quiesced now
(e.g. the vmstat worker) or a future IPI to the core to clean up some
state that could be cleaned up now (e.g. the mm lru per-cpu cache).
In addition, it reqeusts rescheduling if the scheduler dyntick is
still running.

As a result of these tests on the "return to userspace" path, sys
calls (and page faults, etc.) can be inordinately slow.  However,
this quiescing guarantees that no unexpected interrupts will occur,
even if the application intentionally calls into the kernel.

Separate patches that follow provide these changes for x86, tile,
and arm64.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 Documentation/kernel-parameters.txt |   8 ++
 drivers/base/cpu.c                  |  18 +++++
 include/linux/isolation.h           |  48 ++++++++++++
 include/linux/sched.h               |   3 +
 include/linux/tick.h                |   2 +
 include/uapi/linux/prctl.h          |   5 ++
 init/Kconfig                        |  20 +++++
 kernel/Makefile                     |   1 +
 kernel/fork.c                       |   3 +
 kernel/isolation.c                  | 150 ++++++++++++++++++++++++++++++++++++
 kernel/signal.c                     |   3 +
 kernel/sys.c                        |   9 +++
 kernel/time/tick-sched.c            |  33 ++++----
 13 files changed, 289 insertions(+), 14 deletions(-)
 create mode 100644 include/linux/isolation.h
 create mode 100644 kernel/isolation.c

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9a53c929f017..c8d0b42d984a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3747,6 +3747,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			neutralize any effect of /proc/sys/kernel/sysrq.
 			Useful for debugging.
 
+	task_isolation=	[KNL]
+			In kernels built with CONFIG_TASK_ISOLATION=y, set
+			the specified list of CPUs where cpus will be able
+			to use prctl(PR_SET_TASK_ISOLATION) to set up task
+			isolation mode.  Setting this boot flag implicitly
+			also sets up nohz_full and isolcpus mode for the
+			listed set of cpus.
+
 	tcpmhash_entries= [KNL,NET]
 			Set the number of tcp_metrics_hash slots.
 			Default value is 8192 or 16384 depending on total
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 691eeea2f19a..eaf40f4264ee 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -17,6 +17,7 @@
 #include <linux/of.h>
 #include <linux/cpufeature.h>
 #include <linux/tick.h>
+#include <linux/isolation.h>
 
 #include "base.h"
 
@@ -290,6 +291,20 @@ static ssize_t print_cpus_nohz_full(struct device *dev,
 static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
 #endif
 
+#ifdef CONFIG_TASK_ISOLATION
+static ssize_t print_cpus_task_isolation(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	int n = 0, len = PAGE_SIZE-2;
+
+	n = scnprintf(buf, len, "%*pbl\n", cpumask_pr_args(task_isolation_map));
+
+	return n;
+}
+static DEVICE_ATTR(task_isolation, 0444, print_cpus_task_isolation, NULL);
+#endif
+
 static void cpu_device_release(struct device *dev)
 {
 	/*
@@ -460,6 +475,9 @@ static struct attribute *cpu_root_attrs[] = {
 #ifdef CONFIG_NO_HZ_FULL
 	&dev_attr_nohz_full.attr,
 #endif
+#ifdef CONFIG_TASK_ISOLATION
+	&dev_attr_task_isolation.attr,
+#endif
 #ifdef CONFIG_GENERIC_CPU_AUTOPROBE
 	&dev_attr_modalias.attr,
 #endif
diff --git a/include/linux/isolation.h b/include/linux/isolation.h
new file mode 100644
index 000000000000..99b909462e64
--- /dev/null
+++ b/include/linux/isolation.h
@@ -0,0 +1,48 @@
+/*
+ * Task isolation related global functions
+ */
+#ifndef _LINUX_ISOLATION_H
+#define _LINUX_ISOLATION_H
+
+#include <linux/tick.h>
+#include <linux/prctl.h>
+
+#ifdef CONFIG_TASK_ISOLATION
+
+/* cpus that are configured to support task isolation */
+extern cpumask_var_t task_isolation_map;
+
+extern int task_isolation_init(void);
+
+static inline bool task_isolation_possible(int cpu)
+{
+	return task_isolation_map != NULL &&
+		cpumask_test_cpu(cpu, task_isolation_map);
+}
+
+extern int task_isolation_set(unsigned int flags);
+
+extern bool task_isolation_ready(void);
+extern void task_isolation_enter(void);
+
+static inline void task_isolation_set_flags(struct task_struct *p,
+					    unsigned int flags)
+{
+	p->task_isolation_flags = flags;
+
+	if (flags & PR_TASK_ISOLATION_ENABLE)
+		set_tsk_thread_flag(p, TIF_TASK_ISOLATION);
+	else
+		clear_tsk_thread_flag(p, TIF_TASK_ISOLATION);
+}
+
+#else
+static inline void task_isolation_init(void) { }
+static inline bool task_isolation_possible(int cpu) { return false; }
+static inline bool task_isolation_ready(void) { return true; }
+static inline void task_isolation_enter(void) { }
+extern inline void task_isolation_set_flags(struct task_struct *p,
+					    unsigned int flags) { }
+#endif
+
+#endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a10494a94cc3..df6eb22510c3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1830,6 +1830,9 @@ struct task_struct {
 	unsigned long	task_state_change;
 #endif
 	int pagefault_disabled;
+#ifdef CONFIG_TASK_ISOLATION
+	unsigned int	task_isolation_flags;
+#endif
 /* CPU-specific state of this task */
 	struct thread_struct thread;
 /*
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 97fd4e543846..b3841a02dbb7 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -158,6 +158,8 @@ extern void tick_nohz_full_kick(void);
 extern void tick_nohz_full_kick_cpu(int cpu);
 extern void tick_nohz_full_kick_all(void);
 extern void __tick_nohz_task_switch(void);
+extern void tick_nohz_full_add_cpus(const struct cpumask *mask);
+extern bool can_stop_full_tick(void);
 #else
 static inline int housekeeping_any_cpu(void)
 {
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index a8d0759a9e40..67224df4b559 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -197,4 +197,9 @@ struct prctl_mm_map {
 # define PR_CAP_AMBIENT_LOWER		3
 # define PR_CAP_AMBIENT_CLEAR_ALL	4
 
+/* Enable/disable or query task_isolation mode for NO_HZ_FULL kernels. */
+#define PR_SET_TASK_ISOLATION		48
+#define PR_GET_TASK_ISOLATION		49
+# define PR_TASK_ISOLATION_ENABLE	(1 << 0)
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/init/Kconfig b/init/Kconfig
index 22320804fbaf..6cab348fe454 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -782,6 +782,26 @@ config RCU_EXPEDITE_BOOT
 
 endmenu # "RCU Subsystem"
 
+config TASK_ISOLATION
+	bool "Provide hard CPU isolation from the kernel on demand"
+	depends on NO_HZ_FULL
+	help
+	 Allow userspace processes to place themselves on task_isolation
+	 cores and run prctl(PR_SET_TASK_ISOLATION) to "isolate"
+	 themselves from the kernel.  On return to userspace,
+	 isolated tasks will first arrange that no future kernel
+	 activity will interrupt the task while the task is running
+	 in userspace.  This "hard" isolation from the kernel is
+	 required for userspace tasks that are running hard real-time
+	 tasks in userspace, such as a 10 Gbit network driver in userspace.
+
+	 Without this option, but with NO_HZ_FULL enabled, the kernel
+	 will make a best-faith, "soft" effort to shield a single userspace
+	 process from interrupts, but makes no guarantees.
+
+	 You should say "N" unless you are intending to run a
+	 high-performance userspace driver or similar task.
+
 config BUILD_BIN2C
 	bool
 	default n
diff --git a/kernel/Makefile b/kernel/Makefile
index 53abf008ecb3..693a2ba35679 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -103,6 +103,7 @@ obj-$(CONFIG_TORTURE_TEST) += torture.o
 obj-$(CONFIG_MEMBARRIER) += membarrier.o
 
 obj-$(CONFIG_HAS_IOMEM) += memremap.o
+obj-$(CONFIG_TASK_ISOLATION) += isolation.o
 
 $(obj)/configs.o: $(obj)/config_data.h
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 2e391c754ae7..98deb66c9e9e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -75,6 +75,7 @@
 #include <linux/aio.h>
 #include <linux/compiler.h>
 #include <linux/sysctl.h>
+#include <linux/isolation.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -1496,6 +1497,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 #endif
 	clear_all_latency_tracing(p);
 
+	task_isolation_set_flags(p, 0);
+
 	/* ok, now we should be set up.. */
 	p->pid = pid_nr(pid);
 	if (clone_flags & CLONE_THREAD) {
diff --git a/kernel/isolation.c b/kernel/isolation.c
new file mode 100644
index 000000000000..c67f77d217f9
--- /dev/null
+++ b/kernel/isolation.c
@@ -0,0 +1,150 @@
+/*
+ *  linux/kernel/isolation.c
+ *
+ *  Implementation for task isolation.
+ *
+ *  Distributed under GPLv2.
+ */
+
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/vmstat.h>
+#include <linux/isolation.h>
+#include <linux/syscalls.h>
+#include "time/tick-sched.h"
+
+cpumask_var_t task_isolation_map;
+static bool saw_boot_arg;
+
+/*
+ * Isolation requires both nohz and isolcpus support from the scheduler.
+ * We provide a boot flag that enables both for now, and which we can
+ * add other functionality to over time if needed.  Note that just
+ * specifying "nohz_full=... isolcpus=..." does not enable task isolation.
+ */
+static int __init task_isolation_setup(char *str)
+{
+	saw_boot_arg = true;
+
+	alloc_bootmem_cpumask_var(&task_isolation_map);
+	if (cpulist_parse(str, task_isolation_map) < 0) {
+		pr_warn("task_isolation: Incorrect cpumask '%s'\n", str);
+		return 1;
+	}
+
+	return 1;
+}
+__setup("task_isolation=", task_isolation_setup);
+
+int __init task_isolation_init(void)
+{
+	/* For offstack cpumask, ensure we allocate an empty cpumask early. */
+	if (!saw_boot_arg) {
+		zalloc_cpumask_var(&task_isolation_map, GFP_KERNEL);
+		return 0;
+	}
+
+	/*
+	 * Add our task_isolation cpus to nohz_full and isolcpus.  Note
+	 * that we are called relatively early in boot, from tick_init();
+	 * at this point neither nohz_full nor isolcpus has been used
+	 * to configure the system, but isolcpus has been allocated
+	 * already in sched_init().
+	 */
+	tick_nohz_full_add_cpus(task_isolation_map);
+	cpumask_or(cpu_isolated_map, cpu_isolated_map, task_isolation_map);
+
+	return 0;
+}
+
+/*
+ * Get a snapshot of whether, at this moment, it would be possible to
+ * stop the tick.  This test normally requires interrupts disabled since
+ * the condition can change if an interrupt is delivered.  However, in
+ * this case we are using it in an advisory capacity to see if there
+ * is anything obviously indicating that the task isolation
+ * preconditions have not been met, so it's OK that in principle it
+ * might not still be true later in the prctl() syscall path.
+ */
+static bool can_stop_full_tick_now(void)
+{
+	bool ret;
+
+	local_irq_disable();
+	ret = can_stop_full_tick();
+	local_irq_enable();
+	return ret;
+}
+
+/*
+ * This routine controls whether we can enable task-isolation mode.
+ * The task must be affinitized to a single task_isolation core, and
+ * must be at least statically able to stop the nohz_full tick (e.g.,
+ * no other schedulable tasks currently running, no POSIX cpu timers
+ * currently set up, etc.).  If not, we return EINVAL.
+ *
+ * Although the application could later re-affinitize to a
+ * housekeeping core and lose task isolation semantics, or other tasks
+ * could be forcibly scheduled onto this core to restart preemptive
+ * scheduling, etc., this initial test should catch 99% of bugs with
+ * task placement prior to enabling task isolation.
+ */
+int task_isolation_set(unsigned int flags)
+{
+	if (flags != 0 &&
+	    (cpumask_weight(tsk_cpus_allowed(current)) != 1 ||
+	     !task_isolation_possible(raw_smp_processor_id()) ||
+	     !can_stop_full_tick_now()))
+		return -EINVAL;
+
+	task_isolation_set_flags(current, flags);
+	return 0;
+}
+
+/*
+ * In task isolation mode we try to return to userspace only after
+ * attempting to make sure we won't be interrupted again.  This test
+ * is run with interrupts disabled to test that everything we need
+ * to be true is true before we can return to userspace.
+ */
+bool task_isolation_ready(void)
+{
+	WARN_ON_ONCE(!irqs_disabled());
+
+	return (!lru_add_drain_needed(smp_processor_id()) &&
+		vmstat_idle() &&
+		tick_nohz_tick_stopped());
+}
+
+/*
+ * Each time we try to prepare for return to userspace in a process
+ * with task isolation enabled, we run this code to quiesce whatever
+ * subsystems we can readily quiesce to avoid later interrupts.
+ */
+void task_isolation_enter(void)
+{
+	WARN_ON_ONCE(irqs_disabled());
+
+	/* Drain the pagevecs to avoid unnecessary IPI flushes later. */
+	lru_add_drain();
+
+	/* Quieten the vmstat worker so it won't interrupt us. */
+	quiet_vmstat_sync();
+
+	/*
+	 * Request rescheduling unless we are in full dynticks mode.
+	 * We would eventually get pre-empted without this, and if
+	 * there's another task waiting, it would run; but by
+	 * explicitly requesting the reschedule, we may reduce the
+	 * latency.  We could directly call schedule() here as well,
+	 * but since our caller is the standard place where schedule()
+	 * is called, we defer to the caller.
+	 *
+	 * A more substantive approach here would be to use a struct
+	 * completion here explicitly, and complete it when we shut
+	 * down dynticks, but since we presumably have nothing better
+	 * to do on this core anyway, just spinning seems plausible.
+	 */
+	if (!tick_nohz_tick_stopped())
+		set_tsk_need_resched(current);
+}
diff --git a/kernel/signal.c b/kernel/signal.c
index 0508544c8ced..0dd2396345a5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2213,6 +2213,9 @@ relock:
 		/* Trace actually delivered signals. */
 		trace_signal_deliver(signr, &ksig->info, ka);
 
+		/* Disable task isolation when delivering a signal. */
+		task_isolation_set_flags(current, 0);
+
 		if (ka->sa.sa_handler == SIG_IGN) /* Do nothing.  */
 			continue;
 		if (ka->sa.sa_handler != SIG_DFL) {
diff --git a/kernel/sys.c b/kernel/sys.c
index 78947de6f969..c1d621f1137e 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -41,6 +41,7 @@
 #include <linux/syscore_ops.h>
 #include <linux/version.h>
 #include <linux/ctype.h>
+#include <linux/isolation.h>
 
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -2266,6 +2267,14 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 	case PR_GET_FP_MODE:
 		error = GET_FP_MODE(me);
 		break;
+#ifdef CONFIG_TASK_ISOLATION
+	case PR_SET_TASK_ISOLATION:
+		error = task_isolation_set(arg2);
+		break;
+	case PR_GET_TASK_ISOLATION:
+		error = me->task_isolation_flags;
+		break;
+#endif
 	default:
 		error = -EINVAL;
 		break;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 0b17424349eb..2f3d8bc9b2ea 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -24,6 +24,7 @@
 #include <linux/posix-timers.h>
 #include <linux/perf_event.h>
 #include <linux/context_tracking.h>
+#include <linux/isolation.h>
 
 #include <asm/irq_regs.h>
 
@@ -159,7 +160,7 @@ cpumask_var_t tick_nohz_full_mask;
 cpumask_var_t housekeeping_mask;
 bool tick_nohz_full_running;
 
-static bool can_stop_full_tick(void)
+bool can_stop_full_tick(void)
 {
 	WARN_ON_ONCE(!irqs_disabled());
 
@@ -311,30 +312,34 @@ static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
 	return NOTIFY_OK;
 }
 
-static int tick_nohz_init_all(void)
+void tick_nohz_full_add_cpus(const struct cpumask *mask)
 {
-	int err = -1;
+	if (!cpumask_weight(mask))
+		return;
 
-#ifdef CONFIG_NO_HZ_FULL_ALL
-	if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
+	if (tick_nohz_full_mask == NULL &&
+	    !zalloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
 		WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
-		return err;
+		return;
 	}
-	err = 0;
-	cpumask_setall(tick_nohz_full_mask);
+
+	cpumask_or(tick_nohz_full_mask, tick_nohz_full_mask, mask);
 	tick_nohz_full_running = true;
-#endif
-	return err;
 }
 
 void __init tick_nohz_init(void)
 {
 	int cpu;
 
-	if (!tick_nohz_full_running) {
-		if (tick_nohz_init_all() < 0)
-			return;
-	}
+	task_isolation_init();
+
+#ifdef CONFIG_NO_HZ_FULL_ALL
+	if (!tick_nohz_full_running)
+		tick_nohz_full_add_cpus(cpu_possible_mask);
+#endif
+
+	if (!tick_nohz_full_running)
+		return;
 
 	if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
 		WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
-- 
2.7.2

[PATCH v11 05/13] task_isolation: support CONFIG_TASK_ISOLATION_ALL

[Chris Metcalf]

This option, similar to NO_HZ_FULL_ALL, simplifies configuring
a system to boot by default with all cores except the boot core
running in task isolation mode.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 init/Kconfig       | 10 ++++++++++
 kernel/isolation.c |  6 ++++++
 2 files changed, 16 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 6cab348fe454..314b09347fba 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -802,6 +802,16 @@ config TASK_ISOLATION
 	 You should say "N" unless you are intending to run a
 	 high-performance userspace driver or similar task.
 
+config TASK_ISOLATION_ALL
+	bool "Provide task isolation on all CPUs by default (except CPU 0)"
+	depends on TASK_ISOLATION
+	help
+	 If the user doesn't pass the task_isolation boot option to
+	 define the range of task isolation CPUs, consider that all
+	 CPUs in the system are task isolation by default.
+	 Note the boot CPU will still be kept outside the range to
+	 handle timekeeping duty, etc.
+
 config BUILD_BIN2C
 	bool
 	default n
diff --git a/kernel/isolation.c b/kernel/isolation.c
index c67f77d217f9..f59dcf06ba56 100644
--- a/kernel/isolation.c
+++ b/kernel/isolation.c
@@ -40,8 +40,14 @@ int __init task_isolation_init(void)
 {
 	/* For offstack cpumask, ensure we allocate an empty cpumask early. */
 	if (!saw_boot_arg) {
+#ifdef CONFIG_TASK_ISOLATION_ALL
+		alloc_cpumask_var(&task_isolation_map, GFP_KERNEL);
+		cpumask_copy(task_isolation_map, cpu_possible_mask);
+		cpumask_clear_cpu(smp_processor_id(), task_isolation_map);
+#else
 		zalloc_cpumask_var(&task_isolation_map, GFP_KERNEL);
 		return 0;
+#endif
 	}
 
 	/*
-- 
2.7.2

[PATCH v11 06/13] task_isolation: support PR_TASK_ISOLATION_STRICT mode

[Chris Metcalf]

With task_isolation mode, the task is in principle guaranteed not to
be interrupted by the kernel, but only if it behaves.  In particular,
if it enters the kernel via system call, page fault, or any of a
number of other synchronous traps, it may be unexpectedly exposed
to long latencies.  Add a simple flag that puts the process into
a state where any such kernel entry generates a signal.  For system
calls, this test is performed immediately before the SECCOMP test
and causes the syscall to return immediately with ENOSYS.

By default, the task is signalled with SIGKILL, but we add prctl()
bits to support requesting a specific signal instead.

To allow the state to be entered and exited, the syscall checking
test ignores the prctl() syscall so that we can clear the bit again
later, and ignores exit/exit_group to allow exiting the task without
a pointless signal killing you as you try to do so.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 include/linux/isolation.h  | 10 +++++++
 include/uapi/linux/prctl.h |  3 ++
 kernel/isolation.c         | 73 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+)

diff --git a/include/linux/isolation.h b/include/linux/isolation.h
index 99b909462e64..9202ced4511c 100644
--- a/include/linux/isolation.h
+++ b/include/linux/isolation.h
@@ -36,6 +36,14 @@ static inline void task_isolation_set_flags(struct task_struct *p,
 		clear_tsk_thread_flag(p, TIF_TASK_ISOLATION);
 }
 
+extern int task_isolation_syscall(int nr);
+extern void _task_isolation_exception(const char *fmt, ...);
+#define task_isolation_exception(fmt, ...)				\
+	do {								\
+		if (current_thread_info()->flags & _TIF_TASK_ISOLATION) \
+			_task_isolation_exception(fmt, ## __VA_ARGS__); \
+	} while (0)
+
 #else
 static inline void task_isolation_init(void) { }
 static inline bool task_isolation_possible(int cpu) { return false; }
@@ -43,6 +51,8 @@ static inline bool task_isolation_ready(void) { return true; }
 static inline void task_isolation_enter(void) { }
 extern inline void task_isolation_set_flags(struct task_struct *p,
 					    unsigned int flags) { }
+static inline int task_isolation_syscall(int nr) { return 0; }
+static inline void task_isolation_exception(const char *fmt, ...) { }
 #endif
 
 #endif
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 67224df4b559..a5582ace987f 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -201,5 +201,8 @@ struct prctl_mm_map {
 #define PR_SET_TASK_ISOLATION		48
 #define PR_GET_TASK_ISOLATION		49
 # define PR_TASK_ISOLATION_ENABLE	(1 << 0)
+# define PR_TASK_ISOLATION_STRICT	(1 << 1)
+# define PR_TASK_ISOLATION_SET_SIG(sig)	(((sig) & 0x7f) << 8)
+# define PR_TASK_ISOLATION_GET_SIG(bits) (((bits) >> 8) & 0x7f)
 
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/isolation.c b/kernel/isolation.c
index f59dcf06ba56..e1d844b5c567 100644
--- a/kernel/isolation.c
+++ b/kernel/isolation.c
@@ -11,6 +11,8 @@
 #include <linux/vmstat.h>
 #include <linux/isolation.h>
 #include <linux/syscalls.h>
+#include <asm/unistd.h>
+#include <asm/syscall.h>
 #include "time/tick-sched.h"
 
 cpumask_var_t task_isolation_map;
@@ -154,3 +156,74 @@ void task_isolation_enter(void)
 	if (!tick_nohz_tick_stopped())
 		set_tsk_need_resched(current);
 }
+
+void task_isolation_interrupt(struct task_struct *task, const char *buf)
+{
+	siginfo_t info = {};
+	int sig;
+
+	pr_warn("%s/%d: task_isolation strict mode violated by %s\n",
+		task->comm, task->pid, buf);
+
+	/* Get the signal number to use. */
+	sig = PR_TASK_ISOLATION_GET_SIG(task->task_isolation_flags);
+	if (sig == 0)
+		sig = SIGKILL;
+	info.si_signo = sig;
+
+	/*
+	 * Turn off task isolation mode entirely to avoid spamming
+	 * the process with signals.  It can re-enable task isolation
+	 * mode in the signal handler if it wants to.
+	 */
+	task_isolation_set_flags(task, 0);
+
+	send_sig_info(sig, &info, task);
+}
+
+/*
+ * This routine is called from any userspace exception that doesn't
+ * otherwise trigger a signal to the user process (e.g. simple page fault).
+ */
+void _task_isolation_exception(const char *fmt, ...)
+{
+	struct task_struct *task = current;
+
+	/* RCU should have been enabled prior to this point. */
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "kernel entry without RCU");
+
+	if (task->task_isolation_flags & PR_TASK_ISOLATION_STRICT) {
+		va_list args;
+		char buf[100];
+
+		va_start(args, fmt);
+		vsnprintf(buf, sizeof(buf), fmt, args);
+		va_end(args);
+
+		task_isolation_interrupt(task, buf);
+	}
+}
+
+/*
+ * This routine is called from syscall entry (with the syscall number
+ * passed in), and in STRICT mode prevents most syscalls from executing
+ * and raises a signal to notify the process.
+ */
+int task_isolation_syscall(int syscall)
+{
+	struct task_struct *task = current;
+
+	if ((task->task_isolation_flags & PR_TASK_ISOLATION_STRICT) &&
+	    syscall != __NR_prctl &&
+	    syscall != __NR_exit && syscall != __NR_exit_group) {
+		char buf[20];
+
+		snprintf(buf, sizeof(buf), "syscall %d", syscall);
+		task_isolation_interrupt(task, buf);
+
+		syscall_set_return_value(task, current_pt_regs(), ENOSYS, -1);
+		return -1;
+	}
+
+	return 0;
+}
-- 
2.7.2

[PATCH v11 07/13] task_isolation: add debug boot flag

[Chris Metcalf]

The new "task_isolation_debug" flag simplifies debugging
of TASK_ISOLATION kernels when processes are running in
PR_TASK_ISOLATION_ENABLE mode.  Such processes should get no
interrupts from the kernel, and if they do, we notify either the
process (if STRICT mode is set and the interrupt is not an NMI)
or with a kernel stack dump on the console (otherwise).

It's possible to use ftrace to simply detect whether a task_isolation
core has unexpectedly entered the kernel.  But what this boot flag
does is allow the kernel to provide better diagnostics, e.g. by
reporting in the IPI-generating code what remote core and context
is preparing to deliver an interrupt to a task_isolation core.
Additionally, delivering a signal to the process in STRICT mode
allows applications to report up task isolation failures into their
own application logging framework.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 Documentation/kernel-parameters.txt    |  8 ++++
 include/linux/context_tracking_state.h |  6 +++
 include/linux/isolation.h              |  5 +++
 kernel/irq_work.c                      |  5 ++-
 kernel/isolation.c                     | 77 ++++++++++++++++++++++++++++++++++
 kernel/sched/core.c                    | 18 ++++++++
 kernel/signal.c                        |  5 +++
 kernel/smp.c                           |  6 ++-
 kernel/softirq.c                       | 33 +++++++++++++++
 9 files changed, 161 insertions(+), 2 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c8d0b42d984a..ea0434fa906e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3755,6 +3755,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			also sets up nohz_full and isolcpus mode for the
 			listed set of cpus.
 
+	task_isolation_debug	[KNL]
+			In kernels built with CONFIG_TASK_ISOLATION
+			and booted in task_isolation= mode, this
+			setting will generate console backtraces when
+			the kernel is about to interrupt a task that
+			has requested PR_TASK_ISOLATION_ENABLE and is
+			running on a task_isolation core.
+
 	tcpmhash_entries= [KNL,NET]
 			Set the number of tcp_metrics_hash slots.
 			Default value is 8192 or 16384 depending on total
diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index 1d34fe68f48a..4e2c4b900b82 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -39,8 +39,14 @@ static inline bool context_tracking_in_user(void)
 {
 	return __this_cpu_read(context_tracking.state) == CONTEXT_USER;
 }
+
+static inline bool context_tracking_cpu_in_user(int cpu)
+{
+	return per_cpu(context_tracking.state, cpu) == CONTEXT_USER;
+}
 #else
 static inline bool context_tracking_in_user(void) { return false; }
+static inline bool context_tracking_cpu_in_user(int cpu) { return false; }
 static inline bool context_tracking_active(void) { return false; }
 static inline bool context_tracking_is_enabled(void) { return false; }
 static inline bool context_tracking_cpu_is_enabled(void) { return false; }
diff --git a/include/linux/isolation.h b/include/linux/isolation.h
index 9202ced4511c..560608ae72d0 100644
--- a/include/linux/isolation.h
+++ b/include/linux/isolation.h
@@ -44,6 +44,9 @@ extern void _task_isolation_exception(const char *fmt, ...);
 			_task_isolation_exception(fmt, ## __VA_ARGS__); \
 	} while (0)
 
+extern void task_isolation_debug(int cpu);
+extern void task_isolation_debug_cpumask(const struct cpumask *);
+extern void task_isolation_debug_task(int cpu, struct task_struct *p);
 #else
 static inline void task_isolation_init(void) { }
 static inline bool task_isolation_possible(int cpu) { return false; }
@@ -53,6 +56,8 @@ extern inline void task_isolation_set_flags(struct task_struct *p,
 					    unsigned int flags) { }
 static inline int task_isolation_syscall(int nr) { return 0; }
 static inline void task_isolation_exception(const char *fmt, ...) { }
+static inline void task_isolation_debug(int cpu) { }
+#define task_isolation_debug_cpumask(mask) do {} while (0)
 #endif
 
 #endif
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index bcf107ce0854..a9b95ce00667 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -17,6 +17,7 @@
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/smp.h>
+#include <linux/isolation.h>
 #include <asm/processor.h>
 
 
@@ -75,8 +76,10 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
 	if (!irq_work_claim(work))
 		return false;
 
-	if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
+	if (llist_add(&work->llnode, &per_cpu(raised_list, cpu))) {
+		task_isolation_debug(cpu);
 		arch_send_call_function_single_ipi(cpu);
+	}
 
 	return true;
 }
diff --git a/kernel/isolation.c b/kernel/isolation.c
index e1d844b5c567..db281dee7d7e 100644
--- a/kernel/isolation.c
+++ b/kernel/isolation.c
@@ -11,6 +11,7 @@
 #include <linux/vmstat.h>
 #include <linux/isolation.h>
 #include <linux/syscalls.h>
+#include <linux/ratelimit.h>
 #include <asm/unistd.h>
 #include <asm/syscall.h>
 #include "time/tick-sched.h"
@@ -227,3 +228,79 @@ int task_isolation_syscall(int syscall)
 
 	return 0;
 }
+
+/* Enable debugging of any interrupts of task_isolation cores. */
+static int task_isolation_debug_flag;
+static int __init task_isolation_debug_func(char *str)
+{
+	task_isolation_debug_flag = true;
+	return 1;
+}
+__setup("task_isolation_debug", task_isolation_debug_func);
+
+void task_isolation_debug_task(int cpu, struct task_struct *p)
+{
+	static DEFINE_RATELIMIT_STATE(console_output, HZ, 1);
+	bool force_debug = false;
+
+	/*
+	 * Our caller made sure the task was running on a task isolation
+	 * core, but make sure the task has enabled isolation.
+	 */
+	if (!(p->task_isolation_flags & PR_TASK_ISOLATION_ENABLE))
+		return;
+
+	/*
+	 * Ensure the task is actually in userspace; if it is in kernel
+	 * mode, it is expected that it may receive interrupts, and in
+	 * any case they don't affect the isolation.  Note that there
+	 * is a race condition here as a task may have committed
+	 * to returning to user space but not yet set the context
+	 * tracking state to reflect it, and the check here is before
+	 * we trigger the interrupt, so we might fail to warn about a
+	 * legitimate interrupt.  However, the race window is narrow
+	 * and hitting it does not cause any incorrect behavior other
+	 * than failing to send the warning.
+	 */
+	if (!context_tracking_cpu_in_user(cpu))
+		return;
+
+	/*
+	 * If the task was in strict mode, deliver a signal to it.
+	 * We disable task isolation mode when we deliver a signal
+	 * so we won't end up recursing back here again.
+	 * If we are in an NMI, we don't try delivering the signal
+	 * and instead just treat it as if "debug" mode was enabled,
+	 * since that's pretty much all we can do.
+	 */
+	if (p->task_isolation_flags & PR_TASK_ISOLATION_STRICT) {
+		if (in_nmi())
+			force_debug = true;
+		else
+			task_isolation_interrupt(p, "interrupt");
+	}
+
+	/*
+	 * If (for example) the timer interrupt starts ticking
+	 * unexpectedly, we will get an unmanageable flow of output,
+	 * so limit to one backtrace per second.
+	 */
+	if (force_debug ||
+	    (task_isolation_debug_flag && __ratelimit(&console_output))) {
+		pr_err("Interrupt detected for task_isolation cpu %d, %s/%d\n",
+		       cpu, p->comm, p->pid);
+		dump_stack();
+	}
+}
+
+void task_isolation_debug_cpumask(const struct cpumask *mask)
+{
+	int cpu, thiscpu = get_cpu();
+
+	/* No need to report on this cpu since we're already in the kernel. */
+	for_each_cpu(cpu, mask)
+		if (cpu != thiscpu)
+			task_isolation_debug(cpu);
+
+	put_cpu();
+}
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9503d590e5ef..f53e1417aa75 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -74,6 +74,7 @@
 #include <linux/binfmts.h>
 #include <linux/context_tracking.h>
 #include <linux/compiler.h>
+#include <linux/isolation.h>
 
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
@@ -746,6 +747,23 @@ bool sched_can_stop_tick(void)
 }
 #endif /* CONFIG_NO_HZ_FULL */
 
+#ifdef CONFIG_TASK_ISOLATION
+void task_isolation_debug(int cpu)
+{
+	struct task_struct *p;
+
+	if (!task_isolation_possible(cpu))
+		return;
+
+	rcu_read_lock();
+	p = cpu_curr(cpu);
+	get_task_struct(p);
+	rcu_read_unlock();
+	task_isolation_debug_task(cpu, p);
+	put_task_struct(p);
+}
+#endif
+
 void sched_avg_update(struct rq *rq)
 {
 	s64 period = sched_avg_period();
diff --git a/kernel/signal.c b/kernel/signal.c
index 0dd2396345a5..87630ffc0d3a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -34,6 +34,7 @@
 #include <linux/compat.h>
 #include <linux/cn_proc.h>
 #include <linux/compiler.h>
+#include <linux/isolation.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/signal.h>
@@ -638,6 +639,10 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
  */
 void signal_wake_up_state(struct task_struct *t, unsigned int state)
 {
+	/* If the task is being killed, don't complain about task_isolation. */
+	if (state & TASK_WAKEKILL)
+		task_isolation_set_flags(t, 0);
+
 	set_tsk_thread_flag(t, TIF_SIGPENDING);
 	/*
 	 * TASK_WAKEKILL also means wake it up in the stopped/traced/killable
diff --git a/kernel/smp.c b/kernel/smp.c
index d903c02223af..a61894409645 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -14,6 +14,7 @@
 #include <linux/smp.h>
 #include <linux/cpu.h>
 #include <linux/sched.h>
+#include <linux/isolation.h>
 
 #include "smpboot.h"
 
@@ -178,8 +179,10 @@ static int generic_exec_single(int cpu, struct call_single_data *csd,
 	 * locking and barrier primitives. Generic code isn't really
 	 * equipped to do the right thing...
 	 */
-	if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
+	if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu))) {
+		task_isolation_debug(cpu);
 		arch_send_call_function_single_ipi(cpu);
+	}
 
 	return 0;
 }
@@ -457,6 +460,7 @@ void smp_call_function_many(const struct cpumask *mask,
 	}
 
 	/* Send a message to all CPUs in the map */
+	task_isolation_debug_cpumask(cfd->cpumask);
 	arch_send_call_function_ipi_mask(cfd->cpumask);
 
 	if (wait) {
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 479e4436f787..f249b71cddf4 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -26,6 +26,7 @@
 #include <linux/smpboot.h>
 #include <linux/tick.h>
 #include <linux/irq.h>
+#include <linux/isolation.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/irq.h>
@@ -319,6 +320,37 @@ asmlinkage __visible void do_softirq(void)
 	local_irq_restore(flags);
 }
 
+/* Determine whether this IRQ is something task isolation cares about. */
+static void task_isolation_irq(void)
+{
+#ifdef CONFIG_TASK_ISOLATION
+	struct pt_regs *regs;
+
+	if (!context_tracking_cpu_is_enabled())
+		return;
+
+	/*
+	 * We have not yet called __irq_enter() and so we haven't
+	 * adjusted the hardirq count.  This test will allow us to
+	 * avoid false positives for nested IRQs.
+	 */
+	if (in_interrupt())
+		return;
+
+	/*
+	 * If we were already in the kernel, not from an irq but from
+	 * a syscall or synchronous exception/fault, this test should
+	 * avoid a false positive as well.  Note that this requires
+	 * architecture support for calling set_irq_regs() prior to
+	 * calling irq_enter(), and if it's not done consistently, we
+	 * will not consistently avoid false positives here.
+	 */
+	regs = get_irq_regs();
+	if (regs && user_mode(regs))
+		task_isolation_debug(smp_processor_id());
+#endif
+}
+
 /*
  * Enter an interrupt context.
  */
@@ -335,6 +367,7 @@ void irq_enter(void)
 		_local_bh_enable();
 	}
 
+	task_isolation_irq();
 	__irq_enter();
 }
 
-- 
2.7.2

[PATCH v11 08/13] task_isolation: add PR_TASK_ISOLATION_ONE_SHOT flag

[Chris Metcalf]

When this flag is set by the initial prctl(), the semantics of task
isolation change to be "one-shot", i.e. as soon as the kernel is
re-entered for any reason, task isolation is turned off.

During application development, use of this flag is best coupled with
STRICT mode, since otherwise any bug (e.g. an munmap from another
thread in the same task causing an IPI TLB flush) could cause the
task to fall out of task isolation mode without being aware of it.

In production it is typically still best to use STRICT mode, with
a signal handler that will report violations of task isolation
up to the application layer.  However, if you are confident the
application will never fall out of task isolation mode, you may
wish to use ONE_SHOT mode to allow switching from userspace task
isolation mode, to using the kernel freely, without the small extra
penalty of invoking prctl() explicitly to turn task isolation off
before starting to use kernel services.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 include/uapi/linux/prctl.h | 1 +
 kernel/isolation.c         | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index a5582ace987f..1e204f1a0f4a 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -202,6 +202,7 @@ struct prctl_mm_map {
 #define PR_GET_TASK_ISOLATION		49
 # define PR_TASK_ISOLATION_ENABLE	(1 << 0)
 # define PR_TASK_ISOLATION_STRICT	(1 << 1)
+# define PR_TASK_ISOLATION_ONE_SHOT	(1 << 2)
 # define PR_TASK_ISOLATION_SET_SIG(sig)	(((sig) & 0x7f) << 8)
 # define PR_TASK_ISOLATION_GET_SIG(bits) (((bits) >> 8) & 0x7f)
 
diff --git a/kernel/isolation.c b/kernel/isolation.c
index db281dee7d7e..d94a137e0349 100644
--- a/kernel/isolation.c
+++ b/kernel/isolation.c
@@ -202,7 +202,11 @@ void _task_isolation_exception(const char *fmt, ...)
 		va_end(args);
 
 		task_isolation_interrupt(task, buf);
+		return;
 	}
+
+	if (task->task_isolation_flags & PR_TASK_ISOLATION_ONE_SHOT)
+		task_isolation_set_flags(task, 0);
 }
 
 /*
@@ -226,6 +230,9 @@ int task_isolation_syscall(int syscall)
 		return -1;
 	}
 
+	if (task->task_isolation_flags & PR_TASK_ISOLATION_ONE_SHOT)
+		task_isolation_set_flags(task, 0);
+
 	return 0;
 }
 
-- 
2.7.2

[PATCH v11 09/13] arm, tile: turn off timer tick for oneshot_stopped state

[Chris Metcalf]

When the schedule tick is disabled in tick_nohz_stop_sched_tick(),
we call hrtimer_cancel(), which eventually calls down into
__remove_hrtimer() and thus into hrtimer_force_reprogram().
That function's call to tick_program_event() detects that
we are trying to set the expiration to KTIME_MAX and calls
clockevents_switch_state() to set the state to ONESHOT_STOPPED,
and returns.  See commit 8fff52fd5093 ("clockevents: Introduce
CLOCK_EVT_STATE_ONESHOT_STOPPED state") for more background.

However, by default the internal __clockevents_switch_state() code
doesn't have a "set_state_oneshot_stopped" function pointer for
the arm_arch_timer or tile clock_event_device structures, so that
code returns -ENOSYS, and we end up not setting the state, and more
importantly, we don't actually turn off the hardware timer.
As a result, the timer tick we were waiting for before is still
queued, and fires shortly afterwards, only to discover there was
nothing for it to do, at which point it quiesces.

The fix is to provide that function pointer field, and like the
other function pointers, have it just turn off the timer interrupt.
Any call to set a new timer interval will properly re-enable it.

This fix avoids a small performance hiccup for regular applications,
but for TASK_ISOLATION code, it fixes a potentially serious
kernel timer interruption to the time-sensitive application.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 arch/tile/kernel/time.c              | 1 +
 drivers/clocksource/arm_arch_timer.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
index 178989e6d3e3..fbedf380d9d4 100644
--- a/arch/tile/kernel/time.c
+++ b/arch/tile/kernel/time.c
@@ -159,6 +159,7 @@ static DEFINE_PER_CPU(struct clock_event_device, tile_timer) = {
 	.set_next_event = tile_timer_set_next_event,
 	.set_state_shutdown = tile_timer_shutdown,
 	.set_state_oneshot = tile_timer_shutdown,
+	.set_state_oneshot_stopped = tile_timer_shutdown,
 	.tick_resume = tile_timer_shutdown,
 };
 
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index c64d543d64bf..727a669afb1f 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -288,6 +288,8 @@ static void __arch_timer_setup(unsigned type,
 		}
 	}
 
+	clk->set_state_oneshot_stopped = clk->set_state_shutdown;
+
 	clk->set_state_shutdown(clk);
 
 	clockevents_config_and_register(clk, arch_timer_rate, 0xf, 0x7fffffff);
-- 
2.7.2

[PATCH v11 10/13] arch/x86: enable task isolation functionality

[Chris Metcalf]

In prepare_exit_to_usermode(), call task_isolation_ready() for
TIF_TASK_ISOLATION tasks when we are checking the thread-info flags,
and after we've handled the other work, call task_isolation_enter()
for such tasks.

In syscall_trace_enter_phase1(), we add the necessary support for
strict-mode detection of syscalls.

We add strict reporting for the kernel exception types that do
not result in signals, namely non-signalling page faults and
non-signalling MPX fixups.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 arch/x86/entry/common.c            | 18 +++++++++++++++++-
 arch/x86/include/asm/thread_info.h |  2 ++
 arch/x86/kernel/traps.c            |  2 ++
 arch/x86/mm/fault.c                |  2 ++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 03663740c866..62e1e34cffc5 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -21,6 +21,7 @@
 #include <linux/context_tracking.h>
 #include <linux/user-return-notifier.h>
 #include <linux/uprobes.h>
+#include <linux/isolation.h>
 
 #include <asm/desc.h>
 #include <asm/traps.h>
@@ -95,6 +96,13 @@ unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
 	}
 #endif
 
+	/* In isolation mode, we may prevent the syscall from running. */
+	if (work & _TIF_TASK_ISOLATION) {
+		if (task_isolation_syscall(regs->orig_ax) == -1)
+			return -1;
+		work &= ~_TIF_TASK_ISOLATION;
+	}
+
 #ifdef CONFIG_SECCOMP
 	/*
 	 * Do seccomp first -- it should minimize exposure of other
@@ -220,7 +228,7 @@ long syscall_trace_enter(struct pt_regs *regs)
 
 #define EXIT_TO_USERMODE_LOOP_FLAGS				\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
-	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
+	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_TASK_ISOLATION)
 
 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 {
@@ -254,11 +262,19 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 			fire_user_return_notifiers();
 
+		if (cached_flags & _TIF_TASK_ISOLATION)
+			task_isolation_enter();
+
 		/* Disable IRQs and retry */
 		local_irq_disable();
 
 		cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);
 
+		/* Clear task isolation from cached_flags manually. */
+		if ((cached_flags & _TIF_TASK_ISOLATION) &&
+		    task_isolation_ready())
+			cached_flags &= ~_TIF_TASK_ISOLATION;
+
 		if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 			break;
 
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index c7b551028740..5280b92bdc3b 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -97,6 +97,7 @@ struct thread_info {
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_USER_RETURN_NOTIFY	11	/* notify kernel of userspace return */
 #define TIF_UPROBE		12	/* breakpointed or singlestepping */
+#define TIF_TASK_ISOLATION	13	/* task isolation enabled for task */
 #define TIF_NOTSC		16	/* TSC is not accessible in userland */
 #define TIF_IA32		17	/* IA32 compatibility process */
 #define TIF_FORK		18	/* ret_from_fork */
@@ -121,6 +122,7 @@ struct thread_info {
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_USER_RETURN_NOTIFY	(1 << TIF_USER_RETURN_NOTIFY)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
+#define _TIF_TASK_ISOLATION	(1 << TIF_TASK_ISOLATION)
 #define _TIF_NOTSC		(1 << TIF_NOTSC)
 #define _TIF_IA32		(1 << TIF_IA32)
 #define _TIF_FORK		(1 << TIF_FORK)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index ade185a46b1d..bc50c275bb9b 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -36,6 +36,7 @@
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/io.h>
+#include <linux/isolation.h>
 
 #ifdef CONFIG_EISA
 #include <linux/ioport.h>
@@ -398,6 +399,7 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 	case 2:	/* Bound directory has invalid entry. */
 		if (mpx_handle_bd_fault())
 			goto exit_trap;
+		task_isolation_exception("bounds check");
 		break; /* Success, it was handled */
 	case 1: /* Bound violation. */
 		info = mpx_generate_siginfo(regs);
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index e830c71a1323..86def02ff9a0 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -14,6 +14,7 @@
 #include <linux/prefetch.h>		/* prefetchw			*/
 #include <linux/context_tracking.h>	/* exception_enter(), ...	*/
 #include <linux/uaccess.h>		/* faulthandler_disabled()	*/
+#include <linux/isolation.h>		/* task_isolation_exception	*/
 
 #include <asm/traps.h>			/* dotraplinkage, ...		*/
 #include <asm/pgalloc.h>		/* pgd_*(), ...			*/
@@ -1155,6 +1156,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
 		local_irq_enable();
 		error_code |= PF_USER;
 		flags |= FAULT_FLAG_USER;
+		task_isolation_exception("page fault at %#lx", address);
 	} else {
 		if (regs->flags & X86_EFLAGS_IF)
 			local_irq_enable();
-- 
2.7.2

[PATCH v11 11/13] arch/tile: enable task isolation functionality

[Chris Metcalf]

We add the necessary call to task_isolation_enter() in the
prepare_exit_to_usermode() routine.  We already unconditionally
call into this routine if TIF_NOHZ is set, since that's where
we do the user_enter() call.

We add calls to task_isolation_check_exception() in places
where exceptions may not generate signals to the application.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 arch/tile/include/asm/thread_info.h |  4 +++-
 arch/tile/kernel/process.c          |  9 +++++++++
 arch/tile/kernel/ptrace.c           |  7 +++++++
 arch/tile/kernel/single_step.c      |  5 +++++
 arch/tile/kernel/smp.c              | 28 ++++++++++++++++------------
 arch/tile/kernel/unaligned.c        |  3 +++
 arch/tile/mm/fault.c                |  3 +++
 arch/tile/mm/homecache.c            |  2 ++
 8 files changed, 48 insertions(+), 13 deletions(-)

diff --git a/arch/tile/include/asm/thread_info.h b/arch/tile/include/asm/thread_info.h
index 4b7cef9e94e0..ea7fbd0d879d 100644
--- a/arch/tile/include/asm/thread_info.h
+++ b/arch/tile/include/asm/thread_info.h
@@ -126,6 +126,7 @@ extern void _cpu_idle(void);
 #define TIF_SYSCALL_TRACEPOINT	9	/* syscall tracepoint instrumentation */
 #define TIF_POLLING_NRFLAG	10	/* idle is polling for TIF_NEED_RESCHED */
 #define TIF_NOHZ		11	/* in adaptive nohz mode */
+#define TIF_TASK_ISOLATION	12	/* in task isolation mode */
 
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
@@ -139,11 +140,12 @@ extern void _cpu_idle(void);
 #define _TIF_SYSCALL_TRACEPOINT	(1<<TIF_SYSCALL_TRACEPOINT)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_NOHZ		(1<<TIF_NOHZ)
+#define _TIF_TASK_ISOLATION	(1<<TIF_TASK_ISOLATION)
 
 /* Work to do as we loop to exit to user space. */
 #define _TIF_WORK_MASK \
 	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
-	 _TIF_ASYNC_TLB | _TIF_NOTIFY_RESUME)
+	 _TIF_ASYNC_TLB | _TIF_NOTIFY_RESUME | _TIF_TASK_ISOLATION)
 
 /* Work to do on any return to user space. */
 #define _TIF_ALLWORK_MASK \
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index b5f30d376ce1..e752f6c2b645 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -29,6 +29,7 @@
 #include <linux/signal.h>
 #include <linux/delay.h>
 #include <linux/context_tracking.h>
+#include <linux/isolation.h>
 #include <asm/stack.h>
 #include <asm/switch_to.h>
 #include <asm/homecache.h>
@@ -495,9 +496,17 @@ void prepare_exit_to_usermode(struct pt_regs *regs, u32 thread_info_flags)
 			tracehook_notify_resume(regs);
 		}
 
+		if (thread_info_flags & _TIF_TASK_ISOLATION)
+			task_isolation_enter();
+
 		local_irq_disable();
 		thread_info_flags = READ_ONCE(current_thread_info()->flags);
 
+		/* Clear task isolation from cached_flags manually. */
+		if ((thread_info_flags & _TIF_TASK_ISOLATION) &&
+		    task_isolation_ready())
+			thread_info_flags &= ~_TIF_TASK_ISOLATION;
+
 	} while (thread_info_flags & _TIF_WORK_MASK);
 
 	if (thread_info_flags & _TIF_SINGLESTEP) {
diff --git a/arch/tile/kernel/ptrace.c b/arch/tile/kernel/ptrace.c
index 54e7b723db99..475a362415fb 100644
--- a/arch/tile/kernel/ptrace.c
+++ b/arch/tile/kernel/ptrace.c
@@ -23,6 +23,7 @@
 #include <linux/elf.h>
 #include <linux/tracehook.h>
 #include <linux/context_tracking.h>
+#include <linux/isolation.h>
 #include <asm/traps.h>
 #include <arch/chip.h>
 
@@ -255,6 +256,12 @@ int do_syscall_trace_enter(struct pt_regs *regs)
 {
 	u32 work = ACCESS_ONCE(current_thread_info()->flags);
 
+	/* In isolation mode, we may prevent the syscall from running. */
+	if (work & _TIF_TASK_ISOLATION) {
+		if (task_isolation_syscall(regs->regs[TREG_SYSCALL_NR]) == -1)
+			return -1;
+	}
+
 	if (secure_computing() == -1)
 		return -1;
 
diff --git a/arch/tile/kernel/single_step.c b/arch/tile/kernel/single_step.c
index 862973074bf9..3baa7230149e 100644
--- a/arch/tile/kernel/single_step.c
+++ b/arch/tile/kernel/single_step.c
@@ -23,6 +23,7 @@
 #include <linux/types.h>
 #include <linux/err.h>
 #include <linux/prctl.h>
+#include <linux/isolation.h>
 #include <asm/cacheflush.h>
 #include <asm/traps.h>
 #include <asm/uaccess.h>
@@ -320,6 +321,8 @@ void single_step_once(struct pt_regs *regs)
 	int size = 0, sign_ext = 0;  /* happy compiler */
 	int align_ctl;
 
+	task_isolation_exception("single step at %#lx", regs->pc);
+
 	align_ctl = unaligned_fixup;
 	switch (task_thread_info(current)->align_ctl) {
 	case PR_UNALIGN_NOPRINT:
@@ -767,6 +770,8 @@ void single_step_once(struct pt_regs *regs)
 	unsigned long *ss_pc = this_cpu_ptr(&ss_saved_pc);
 	unsigned long control = __insn_mfspr(SPR_SINGLE_STEP_CONTROL_K);
 
+	task_isolation_exception("single step at %#lx", regs->pc);
+
 	*ss_pc = regs->pc;
 	control |= SPR_SINGLE_STEP_CONTROL_1__CANCELED_MASK;
 	control |= SPR_SINGLE_STEP_CONTROL_1__INHIBIT_MASK;
diff --git a/arch/tile/kernel/smp.c b/arch/tile/kernel/smp.c
index 07e3ff5cc740..da1eb240fc57 100644
--- a/arch/tile/kernel/smp.c
+++ b/arch/tile/kernel/smp.c
@@ -20,6 +20,7 @@
 #include <linux/irq.h>
 #include <linux/irq_work.h>
 #include <linux/module.h>
+#include <linux/isolation.h>
 #include <asm/cacheflush.h>
 #include <asm/homecache.h>
 
@@ -67,6 +68,7 @@ void send_IPI_single(int cpu, int tag)
 		.x = cpu % smp_width,
 		.state = HV_TO_BE_SENT
 	};
+	task_isolation_debug(cpu);
 	__send_IPI_many(&recip, 1, tag);
 }
 
@@ -84,6 +86,7 @@ void send_IPI_many(const struct cpumask *mask, int tag)
 		r->x = cpu % smp_width;
 		r->state = HV_TO_BE_SENT;
 	}
+	task_isolation_debug_cpumask(mask);
 	__send_IPI_many(recip, nrecip, tag);
 }
 
@@ -181,10 +184,11 @@ void flush_icache_range(unsigned long start, unsigned long end)
 	struct ipi_flush flush = { start, end };
 
 	/* If invoked with irqs disabled, we can not issue IPIs. */
-	if (irqs_disabled())
+	if (irqs_disabled()) {
+		task_isolation_debug_cpumask(task_isolation_map);
 		flush_remote(0, HV_FLUSH_EVICT_L1I, NULL, 0, 0, 0,
 			NULL, NULL, 0);
-	else {
+	} else {
 		preempt_disable();
 		on_each_cpu(ipi_flush_icache_range, &flush, 1);
 		preempt_enable();
@@ -258,10 +262,8 @@ void __init ipi_init(void)
 
 #if CHIP_HAS_IPI()
 
-void smp_send_reschedule(int cpu)
+static void __smp_send_reschedule(int cpu)
 {
-	WARN_ON(cpu_is_offline(cpu));
-
 	/*
 	 * We just want to do an MMIO store.  The traditional writeq()
 	 * functions aren't really correct here, since they're always
@@ -273,15 +275,17 @@ void smp_send_reschedule(int cpu)
 
 #else
 
-void smp_send_reschedule(int cpu)
+static void __smp_send_reschedule(int cpu)
 {
-	HV_Coord coord;
-
-	WARN_ON(cpu_is_offline(cpu));
-
-	coord.y = cpu_y(cpu);
-	coord.x = cpu_x(cpu);
+	HV_Coord coord = { .y = cpu_y(cpu), .x = cpu_x(cpu) };
 	hv_trigger_ipi(coord, IRQ_RESCHEDULE);
 }
 
 #endif /* CHIP_HAS_IPI() */
+
+void smp_send_reschedule(int cpu)
+{
+	WARN_ON(cpu_is_offline(cpu));
+	task_isolation_debug(cpu);
+	__smp_send_reschedule(cpu);
+}
diff --git a/arch/tile/kernel/unaligned.c b/arch/tile/kernel/unaligned.c
index 0db5f7c9d9e5..754204987532 100644
--- a/arch/tile/kernel/unaligned.c
+++ b/arch/tile/kernel/unaligned.c
@@ -25,6 +25,7 @@
 #include <linux/module.h>
 #include <linux/compat.h>
 #include <linux/prctl.h>
+#include <linux/isolation.h>
 #include <asm/cacheflush.h>
 #include <asm/traps.h>
 #include <asm/uaccess.h>
@@ -1545,6 +1546,8 @@ void do_unaligned(struct pt_regs *regs, int vecnum)
 		return;
 	}
 
+	task_isolation_exception("unaligned JIT at %#lx", regs->pc);
+
 	if (!info->unalign_jit_base) {
 		void __user *user_page;
 
diff --git a/arch/tile/mm/fault.c b/arch/tile/mm/fault.c
index 26734214818c..7f910e4061f1 100644
--- a/arch/tile/mm/fault.c
+++ b/arch/tile/mm/fault.c
@@ -35,6 +35,7 @@
 #include <linux/syscalls.h>
 #include <linux/uaccess.h>
 #include <linux/kdebug.h>
+#include <linux/isolation.h>
 
 #include <asm/pgalloc.h>
 #include <asm/sections.h>
@@ -844,6 +845,8 @@ static inline void __do_page_fault(struct pt_regs *regs, int fault_num,
 void do_page_fault(struct pt_regs *regs, int fault_num,
 		   unsigned long address, unsigned long write)
 {
+	task_isolation_exception("page fault interrupt %d at %#lx (%#lx)",
+				       fault_num, regs->pc, address);
 	__do_page_fault(regs, fault_num, address, write);
 }
 
diff --git a/arch/tile/mm/homecache.c b/arch/tile/mm/homecache.c
index 40ca30a9fee3..e044e8dd8372 100644
--- a/arch/tile/mm/homecache.c
+++ b/arch/tile/mm/homecache.c
@@ -31,6 +31,7 @@
 #include <linux/smp.h>
 #include <linux/module.h>
 #include <linux/hugetlb.h>
+#include <linux/isolation.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -83,6 +84,7 @@ static void hv_flush_update(const struct cpumask *cache_cpumask,
 	 * Don't bother to update atomically; losing a count
 	 * here is not that critical.
 	 */
+	task_isolation_debug_cpumask(&mask);
 	for_each_cpu(cpu, &mask)
 		++per_cpu(irq_stat, cpu).irq_hv_flush_count;
 }
-- 
2.7.2

[PATCH v11 12/13] arm64: factor work_pending state machine to C

[Chris Metcalf]

Currently ret_fast_syscall, work_pending, and ret_to_user form an ad-hoc
state machine that can be difficult to reason about due to duplicated
code and a large number of branch targets.

This patch factors the common logic out into the existing
do_notify_resume function, converting the code to C in the process,
making the code more legible.

This patch tries to closely mirror the existing behaviour while using
the usual C control flow primitives. As local_irq_{disable,enable} may
be instrumented, we balance exception entry (where we will almost most
likely enable IRQs) with a call to trace_hardirqs_on just before the
return to userspace.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 arch/arm64/kernel/entry.S  | 12 ++++--------
 arch/arm64/kernel/signal.c | 36 ++++++++++++++++++++++++++----------
 2 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 1f7f5a2b61bf..966d0d4308f2 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -674,18 +674,13 @@ ret_fast_syscall_trace:
  * Ok, we need to do extra processing, enter the slow path.
  */
 work_pending:
-	tbnz	x1, #TIF_NEED_RESCHED, work_resched
-	/* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */
 	mov	x0, sp				// 'regs'
-	enable_irq				// enable interrupts for do_notify_resume()
 	bl	do_notify_resume
-	b	ret_to_user
-work_resched:
 #ifdef CONFIG_TRACE_IRQFLAGS
-	bl	trace_hardirqs_off		// the IRQs are off here, inform the tracing code
+	bl	trace_hardirqs_on		// enabled while in userspace
 #endif
-	bl	schedule
-
+	ldr	x1, [tsk, #TI_FLAGS]		// re-check for single-step
+	b	finish_ret_to_user
 /*
  * "slow" syscall return path.
  */
@@ -694,6 +689,7 @@ ret_to_user:
 	ldr	x1, [tsk, #TI_FLAGS]
 	and	x2, x1, #_TIF_WORK_MASK
 	cbnz	x2, work_pending
+finish_ret_to_user:
 	enable_step_tsk x1, x2
 	kernel_exit 0
 ENDPROC(ret_to_user)
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index e18c48cb6db1..1f172f8afe47 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -402,15 +402,31 @@ static void do_signal(struct pt_regs *regs)
 asmlinkage void do_notify_resume(struct pt_regs *regs,
 				 unsigned int thread_flags)
 {
-	if (thread_flags & _TIF_SIGPENDING)
-		do_signal(regs);
-
-	if (thread_flags & _TIF_NOTIFY_RESUME) {
-		clear_thread_flag(TIF_NOTIFY_RESUME);
-		tracehook_notify_resume(regs);
-	}
-
-	if (thread_flags & _TIF_FOREIGN_FPSTATE)
-		fpsimd_restore_current_state();
+	/*
+	 * The assembly code enters us with IRQs off, but it hasn't
+	 * informed the tracing code of that for efficiency reasons.
+	 * Update the trace code with the current status.
+	 */
+	trace_hardirqs_off();
+	do {
+		if (thread_flags & _TIF_NEED_RESCHED) {
+			schedule();
+		} else {
+			local_irq_enable();
+
+			if (thread_flags & _TIF_SIGPENDING)
+				do_signal(regs);
+
+			if (thread_flags & _TIF_NOTIFY_RESUME) {
+				clear_thread_flag(TIF_NOTIFY_RESUME);
+				tracehook_notify_resume(regs);
+			}
+
+			if (thread_flags & _TIF_FOREIGN_FPSTATE)
+				fpsimd_restore_current_state();
+		}
 
+		local_irq_disable();
+		thread_flags = READ_ONCE(current_thread_info()->flags);
+	} while (thread_flags & _TIF_WORK_MASK);
 }
-- 
2.7.2

[PATCH v11 13/13] arch/arm64: enable task isolation functionality

[Chris Metcalf]

In do_notify_resume(), call task_isolation_ready() for
TIF_TASK_ISOLATION tasks when we are checking the thread-info flags;
and after we've handled the other work, call task_isolation_enter()
for such tasks.  To ensure we always call task_isolation_enter() when
returning to userspace, add _TIF_TASK_ISOLATION to _TIF_WORK_MASK,
while leaving the old bitmask value as _TIF_WORK_LOOP_MASK to
check while looping.

We tweak syscall_trace_enter() slightly to carry the "flags"
value from current_thread_info()->flags for each of the tests,
rather than doing a volatile read from memory for each one.  This
avoids a small overhead for each test, and in particular avoids
that overhead for TIF_NOHZ when TASK_ISOLATION is not enabled.

We instrument the smp_cross_call() routine so that it checks for
isolated tasks and generates a suitable warning if we are about
to disturb one of them in strict or debug mode.

Finally, add an explicit check for STRICT mode in do_mem_abort()
to handle the case of page faults.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 arch/arm64/include/asm/thread_info.h |  5 ++++-
 arch/arm64/kernel/ptrace.c           | 15 ++++++++++++---
 arch/arm64/kernel/signal.c           | 10 ++++++++++
 arch/arm64/kernel/smp.c              |  2 ++
 arch/arm64/mm/fault.c                |  4 ++++
 5 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index abd64bd1f6d9..bdc6426b9968 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -109,6 +109,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_NEED_RESCHED	1
 #define TIF_NOTIFY_RESUME	2	/* callback before returning to user */
 #define TIF_FOREIGN_FPSTATE	3	/* CPU's FP state is not current's */
+#define TIF_TASK_ISOLATION	4
 #define TIF_NOHZ		7
 #define TIF_SYSCALL_TRACE	8
 #define TIF_SYSCALL_AUDIT	9
@@ -124,6 +125,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_FOREIGN_FPSTATE	(1 << TIF_FOREIGN_FPSTATE)
+#define _TIF_TASK_ISOLATION	(1 << TIF_TASK_ISOLATION)
 #define _TIF_NOHZ		(1 << TIF_NOHZ)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
@@ -132,7 +134,8 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_32BIT		(1 << TIF_32BIT)
 
 #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
-				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE)
+				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
+				 _TIF_TASK_ISOLATION)
 
 #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
 				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index ff7f13239515..6fbb70112e11 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -37,6 +37,7 @@
 #include <linux/regset.h>
 #include <linux/tracehook.h>
 #include <linux/elf.h>
+#include <linux/isolation.h>
 
 #include <asm/compat.h>
 #include <asm/debug-monitors.h>
@@ -1246,14 +1247,22 @@ static void tracehook_report_syscall(struct pt_regs *regs,
 
 asmlinkage int syscall_trace_enter(struct pt_regs *regs)
 {
-	/* Do the secure computing check first; failures should be fast. */
+	unsigned long work = ACCESS_ONCE(current_thread_info()->flags);
+
+	/* In isolation mode, we may prevent the syscall from running. */
+	if (work & _TIF_TASK_ISOLATION) {
+		if (task_isolation_syscall(regs->syscallno) == -1)
+			return -1;
+	}
+
+	/* Do the secure computing check early; failures should be fast. */
 	if (secure_computing() == -1)
 		return -1;
 
-	if (test_thread_flag(TIF_SYSCALL_TRACE))
+	if (work & _TIF_SYSCALL_TRACE)
 		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
 
-	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+	if (work & _TIF_SYSCALL_TRACEPOINT)
 		trace_sys_enter(regs, regs->syscallno);
 
 	audit_syscall_entry(regs->syscallno, regs->orig_x0, regs->regs[1],
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 1f172f8afe47..1e6ee84bd6ca 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -25,6 +25,7 @@
 #include <linux/uaccess.h>
 #include <linux/tracehook.h>
 #include <linux/ratelimit.h>
+#include <linux/isolation.h>
 
 #include <asm/debug-monitors.h>
 #include <asm/elf.h>
@@ -424,9 +425,18 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 
 			if (thread_flags & _TIF_FOREIGN_FPSTATE)
 				fpsimd_restore_current_state();
+
+			if (thread_flags & _TIF_TASK_ISOLATION)
+				task_isolation_enter();
 		}
 
 		local_irq_disable();
 		thread_flags = READ_ONCE(current_thread_info()->flags);
+
+		/* Clear task isolation from cached_flags manually. */
+		if ((thread_flags & _TIF_TASK_ISOLATION) &&
+		    task_isolation_ready())
+			thread_flags &= ~_TIF_TASK_ISOLATION;
+
 	} while (thread_flags & _TIF_WORK_MASK);
 }
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index b1adc51b2c2e..dcb3282d04a2 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -37,6 +37,7 @@
 #include <linux/completion.h>
 #include <linux/of.h>
 #include <linux/irq_work.h>
+#include <linux/isolation.h>
 
 #include <asm/alternative.h>
 #include <asm/atomic.h>
@@ -632,6 +633,7 @@ static const char *ipi_types[NR_IPI] __tracepoint_string = {
 static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
 {
 	trace_ipi_raise(target, ipi_types[ipinr]);
+	task_isolation_debug_cpumask(target);
 	__smp_cross_call(target, ipinr);
 }
 
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index abe2a9542b3a..d9b5119328eb 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -29,6 +29,7 @@
 #include <linux/sched.h>
 #include <linux/highmem.h>
 #include <linux/perf_event.h>
+#include <linux/isolation.h>
 
 #include <asm/cpufeature.h>
 #include <asm/exception.h>
@@ -473,6 +474,9 @@ asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
 	const struct fault_info *inf = fault_info + (esr & 63);
 	struct siginfo info;
 
+	if (user_mode(regs))
+		task_isolation_exception("%s at %#lx", inf->name, addr);
+
 	if (!inf->fn(addr, esr, regs))
 		return;
 
-- 
2.7.2

Re: [PATCH v11 12/13] arm64: factor work_pending state machine to C

[Chris Metcalf]

Just wanted to ping this one part of the patch series that hopefully
could be picked up in time for the 4.6 rc1 merge window, even if
the rest of the patch series ends up taking longer to get through.
Will, does that seem like something worth trying to do?

I'm hoping that the performance issues you saw with Mark's
original patch are improved with this version, which still tests
the TIF flags prior to calling out to the loop in C code.

Thanks!

On 03/11/2016 05:10 PM, Chris Metcalf wrote:
> Currently ret_fast_syscall, work_pending, and ret_to_user form an ad-hoc
> state machine that can be difficult to reason about due to duplicated
> code and a large number of branch targets.
>
> This patch factors the common logic out into the existing
> do_notify_resume function, converting the code to C in the process,
> making the code more legible.
>
> This patch tries to closely mirror the existing behaviour while using
> the usual C control flow primitives. As local_irq_{disable,enable} may
> be instrumented, we balance exception entry (where we will almost most
> likely enable IRQs) with a call to trace_hardirqs_on just before the
> return to userspace.
>
> Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
> ---
>   arch/arm64/kernel/entry.S  | 12 ++++--------
>   arch/arm64/kernel/signal.c | 36 ++++++++++++++++++++++++++----------
>   2 files changed, 30 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 1f7f5a2b61bf..966d0d4308f2 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -674,18 +674,13 @@ ret_fast_syscall_trace:
>    * Ok, we need to do extra processing, enter the slow path.
>    */
>   work_pending:
> -	tbnz	x1, #TIF_NEED_RESCHED, work_resched
> -	/* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */
>   	mov	x0, sp				// 'regs'
> -	enable_irq				// enable interrupts for do_notify_resume()
>   	bl	do_notify_resume
> -	b	ret_to_user
> -work_resched:
>   #ifdef CONFIG_TRACE_IRQFLAGS
> -	bl	trace_hardirqs_off		// the IRQs are off here, inform the tracing code
> +	bl	trace_hardirqs_on		// enabled while in userspace
>   #endif
> -	bl	schedule
> -
> +	ldr	x1, [tsk, #TI_FLAGS]		// re-check for single-step
> +	b	finish_ret_to_user
>   /*
>    * "slow" syscall return path.
>    */
> @@ -694,6 +689,7 @@ ret_to_user:
>   	ldr	x1, [tsk, #TI_FLAGS]
>   	and	x2, x1, #_TIF_WORK_MASK
>   	cbnz	x2, work_pending
> +finish_ret_to_user:
>   	enable_step_tsk x1, x2
>   	kernel_exit 0
>   ENDPROC(ret_to_user)
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index e18c48cb6db1..1f172f8afe47 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -402,15 +402,31 @@ static void do_signal(struct pt_regs *regs)
>   asmlinkage void do_notify_resume(struct pt_regs *regs,
>   				 unsigned int thread_flags)
>   {
> -	if (thread_flags & _TIF_SIGPENDING)
> -		do_signal(regs);
> -
> -	if (thread_flags & _TIF_NOTIFY_RESUME) {
> -		clear_thread_flag(TIF_NOTIFY_RESUME);
> -		tracehook_notify_resume(regs);
> -	}
> -
> -	if (thread_flags & _TIF_FOREIGN_FPSTATE)
> -		fpsimd_restore_current_state();
> +	/*
> +	 * The assembly code enters us with IRQs off, but it hasn't
> +	 * informed the tracing code of that for efficiency reasons.
> +	 * Update the trace code with the current status.
> +	 */
> +	trace_hardirqs_off();
> +	do {
> +		if (thread_flags & _TIF_NEED_RESCHED) {
> +			schedule();
> +		} else {
> +			local_irq_enable();
> +
> +			if (thread_flags & _TIF_SIGPENDING)
> +				do_signal(regs);
> +
> +			if (thread_flags & _TIF_NOTIFY_RESUME) {
> +				clear_thread_flag(TIF_NOTIFY_RESUME);
> +				tracehook_notify_resume(regs);
> +			}
> +
> +			if (thread_flags & _TIF_FOREIGN_FPSTATE)
> +				fpsimd_restore_current_state();
> +		}
>   
> +		local_irq_disable();
> +		thread_flags = READ_ONCE(current_thread_info()->flags);
> +	} while (thread_flags & _TIF_WORK_MASK);
>   }

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com

Re: [PATCH v11 01/13] vmstat: add quiet_vmstat_sync function

[Michal Hocko]

On Fri 11-03-16 17:10:11, Chris Metcalf wrote:
> In commit f01f17d3705b ("mm, vmstat: make quiet_vmstat lighter")
> the quiet_vmstat() function became asynchronous, in the sense that
> the vmstat work was still scheduled to run on the core when the
> function returned.  For task isolation, we need a synchronous
> version of the function that guarantees that the vmstat worker
> will not run on the core on return from the function.  Add a
> quiet_vmstat_sync() function with that semantic.

The full series hasn't reached my inbox and from the above it is not
really clear where is the new function supposed to be used.

It is usually preferable to include the consumer of the new API in the
same patch. Is this case any special that it couldn't be done that way?

> Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
> ---
>  include/linux/vmstat.h | 2 ++
>  mm/vmstat.c            | 9 +++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index 73fae8c4a5fb..43b2f1c33266 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -190,6 +190,7 @@ extern void dec_zone_state(struct zone *, enum zone_stat_item);
>  extern void __dec_zone_state(struct zone *, enum zone_stat_item);
>  
>  void quiet_vmstat(void);
> +void quiet_vmstat_sync(void);
>  void cpu_vm_stats_fold(int cpu);
>  void refresh_zone_stat_thresholds(void);
>  
> @@ -251,6 +252,7 @@ static inline void __dec_zone_page_state(struct page *page,
>  static inline void refresh_zone_stat_thresholds(void) { }
>  static inline void cpu_vm_stats_fold(int cpu) { }
>  static inline void quiet_vmstat(void) { }
> +static inline void quiet_vmstat_sync(void) { }
>  
>  static inline void drain_zonestat(struct zone *zone,
>  			struct per_cpu_pageset *pset) { }
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 084c6725b373..ff569246fcb5 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1469,6 +1469,15 @@ void quiet_vmstat(void)
>  	refresh_cpu_vm_stats(false);
>  }
>  
> +/*
> + * Synchronously quiet vmstat so the work is guaranteed not to run on return.
> + */
> +void quiet_vmstat_sync(void)
> +{
> +	cpumask_set_cpu(smp_processor_id(), cpu_stat_off);
> +	cancel_delayed_work_sync(this_cpu_ptr(&vmstat_work));
> +	refresh_cpu_vm_stats(false);
> +}
>  
>  /*
>   * Shepherd worker thread that checks the
> -- 
> 2.7.2
> 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v11 01/13] vmstat: add quiet_vmstat_sync function

[Chris Metcalf]

On 03/21/2016 10:34 AM, Michal Hocko wrote:
> On Fri 11-03-16 17:10:11, Chris Metcalf wrote:
>> In commit f01f17d3705b ("mm, vmstat: make quiet_vmstat lighter")
>> the quiet_vmstat() function became asynchronous, in the sense that
>> the vmstat work was still scheduled to run on the core when the
>> function returned.  For task isolation, we need a synchronous
>> version of the function that guarantees that the vmstat worker
>> will not run on the core on return from the function.  Add a
>> quiet_vmstat_sync() function with that semantic.
> The full series hasn't reached my inbox and from the above it is not
> really clear where is the new function supposed to be used.
>
> It is usually preferable to include the consumer of the new API in the
> same patch. Is this case any special that it couldn't be done that way?

I've seen this done both ways (i.e. smushing things all together, vs
breaking them apart) and my sense is that particularly for larger patch
series, keeping individual atomic patches that bisect cleanly is the
better choice.

In this particular case, there are a three patches in mm that all
individually are needed for task isolation; merging all three into
the patch that enables task isolation would have made that patch even
larger and harder to review.  (Similarly, one could argue that even
that patch on its own does nothing, and is purely an enablement patch
for the various architecture-specific follow-on patches that actually
provide the hooks to make it work, so by your argument perhaps the
whole thing should be merged into a single giant patch...)

In any case, I think you are absolutely right that providing more
context to reviewers is the right thing, and I'll make sure in future
patch series to include all the reviewers from "enabling patches" into
the patch that uses the particular enablement.  For this series, the
patch that uses the quiet_vmstat_sync() call is here:

https://lkml.kernel.org/r/1457734223-26209-5-git-send-email-cmetcalf@mellanox.com

The cover letter email is here if you're curious for more context:

https://lkml.kernel.org/r/1457734223-26209-1-git-send-email-cmetcalf@mellanox.com

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com