[PATCH v10 00/16] Add support for 32-bit tasks on asymmetric AArch32 systems

[PATCH v10 00/16] Add support for 32-bit tasks on asymmetric AArch32 systems

[Will Deacon]

Hi again all,

This is version TEN of the patches previously circulated at:

  v1: https://lore.kernel.org/r/20201027215118.27003-1-will@kernel.org
  v2: https://lore.kernel.org/r/20201109213023.15092-1-will@kernel.org
  v3: https://lore.kernel.org/r/20201113093720.21106-1-will@kernel.org
  v4: https://lore.kernel.org/r/20201124155039.13804-1-will@kernel.org
  v5: https://lore.kernel.org/r/20201208132835.6151-1-will@kernel.org
  v6: https://lore.kernel.org/r/20210518094725.7701-1-will@kernel.org
  v7: https://lore.kernel.org/r/20210525151432.16875-1-will@kernel.org
  v8: https://lore.kernel.org/r/20210602164719.31777-1-will@kernel.org
  v9: https://lore.kernel.org/r/20210608180313.11502-1-will@kernel.org

There was also a nice LWN writeup in case you've forgotten what this is
about:

	https://lwn.net/Articles/838339/

The only changes since v9 are that I've added some Reviewed-by tags from
Valentin and rebased the series onto the stable arm64/for-next/cpufeature
branch, where I have queued some of the arm64 prerequisites [1].

Cheers,

Will

[1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/cpufeature

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Qais Yousef <qais.yousef@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Quentin Perret <qperret@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: kernel-team@android.com

--->8

Will Deacon (16):
  sched: Introduce task_cpu_possible_mask() to limit fallback rq
    selection
  cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1
  cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()
  cpuset: Cleanup cpuset_cpus_allowed_fallback() use in
    select_fallback_rq()
  sched: Reject CPU affinity changes based on task_cpu_possible_mask()
  sched: Introduce task_struct::user_cpus_ptr to track requested
    affinity
  sched: Split the guts of sched_setaffinity() into a helper function
  sched: Allow task CPU affinity to be restricted on asymmetric systems
  sched: Introduce dl_task_check_affinity() to check proposed affinity
  arm64: Implement task_cpu_possible_mask()
  arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit
    EL0
  arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched
    system
  arm64: Advertise CPUs capable of running 32-bit applications in sysfs
  arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0
  arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores
  Documentation: arm64: describe asymmetric 32-bit support

 .../ABI/testing/sysfs-devices-system-cpu      |   9 +
 .../admin-guide/kernel-parameters.txt         |  11 +
 Documentation/arm64/asymmetric-32bit.rst      | 155 ++++++++
 Documentation/arm64/index.rst                 |   1 +
 arch/arm64/include/asm/elf.h                  |   6 +-
 arch/arm64/include/asm/mmu_context.h          |  13 +
 arch/arm64/kernel/cpufeature.c                |  51 ++-
 arch/arm64/kernel/process.c                   |  47 ++-
 arch/arm64/kernel/signal.c                    |  26 --
 include/linux/cpuset.h                        |   8 +-
 include/linux/mmu_context.h                   |  14 +
 include/linux/sched.h                         |  21 ++
 init/init_task.c                              |   1 +
 kernel/cgroup/cpuset.c                        |  59 +--
 kernel/fork.c                                 |   2 +
 kernel/sched/core.c                           | 340 ++++++++++++++----
 kernel/sched/sched.h                          |   1 +
 17 files changed, 627 insertions(+), 138 deletions(-)
 create mode 100644 Documentation/arm64/asymmetric-32bit.rst

-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 00/16] Add support for 32-bit tasks on asymmetric AArch32 systems

[Will Deacon]

Hi again all,

This is version TEN of the patches previously circulated at:

  v1: https://lore.kernel.org/r/20201027215118.27003-1-will@kernel.org
  v2: https://lore.kernel.org/r/20201109213023.15092-1-will@kernel.org
  v3: https://lore.kernel.org/r/20201113093720.21106-1-will@kernel.org
  v4: https://lore.kernel.org/r/20201124155039.13804-1-will@kernel.org
  v5: https://lore.kernel.org/r/20201208132835.6151-1-will@kernel.org
  v6: https://lore.kernel.org/r/20210518094725.7701-1-will@kernel.org
  v7: https://lore.kernel.org/r/20210525151432.16875-1-will@kernel.org
  v8: https://lore.kernel.org/r/20210602164719.31777-1-will@kernel.org
  v9: https://lore.kernel.org/r/20210608180313.11502-1-will@kernel.org

There was also a nice LWN writeup in case you've forgotten what this is
about:

	https://lwn.net/Articles/838339/

The only changes since v9 are that I've added some Reviewed-by tags from
Valentin and rebased the series onto the stable arm64/for-next/cpufeature
branch, where I have queued some of the arm64 prerequisites [1].

Cheers,

Will

[1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/cpufeature

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Qais Yousef <qais.yousef@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Quentin Perret <qperret@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: kernel-team@android.com

--->8

Will Deacon (16):
  sched: Introduce task_cpu_possible_mask() to limit fallback rq
    selection
  cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1
  cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()
  cpuset: Cleanup cpuset_cpus_allowed_fallback() use in
    select_fallback_rq()
  sched: Reject CPU affinity changes based on task_cpu_possible_mask()
  sched: Introduce task_struct::user_cpus_ptr to track requested
    affinity
  sched: Split the guts of sched_setaffinity() into a helper function
  sched: Allow task CPU affinity to be restricted on asymmetric systems
  sched: Introduce dl_task_check_affinity() to check proposed affinity
  arm64: Implement task_cpu_possible_mask()
  arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit
    EL0
  arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched
    system
  arm64: Advertise CPUs capable of running 32-bit applications in sysfs
  arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0
  arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores
  Documentation: arm64: describe asymmetric 32-bit support

 .../ABI/testing/sysfs-devices-system-cpu      |   9 +
 .../admin-guide/kernel-parameters.txt         |  11 +
 Documentation/arm64/asymmetric-32bit.rst      | 155 ++++++++
 Documentation/arm64/index.rst                 |   1 +
 arch/arm64/include/asm/elf.h                  |   6 +-
 arch/arm64/include/asm/mmu_context.h          |  13 +
 arch/arm64/kernel/cpufeature.c                |  51 ++-
 arch/arm64/kernel/process.c                   |  47 ++-
 arch/arm64/kernel/signal.c                    |  26 --
 include/linux/cpuset.h                        |   8 +-
 include/linux/mmu_context.h                   |  14 +
 include/linux/sched.h                         |  21 ++
 init/init_task.c                              |   1 +
 kernel/cgroup/cpuset.c                        |  59 +--
 kernel/fork.c                                 |   2 +
 kernel/sched/core.c                           | 340 ++++++++++++++----
 kernel/sched/sched.h                          |   1 +
 17 files changed, 627 insertions(+), 138 deletions(-)
 create mode 100644 Documentation/arm64/asymmetric-32bit.rst

-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 01/16] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection

[Will Deacon]

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

On such a system, we must take care not to migrate a task to an
unsupported CPU when forcefully moving tasks in select_fallback_rq()
in response to a CPU hot-unplug operation.

Introduce a task_cpu_possible_mask() hook which, given a task argument,
allows an architecture to return a cpumask of CPUs that are capable of
executing that task. The default implementation returns the
cpu_possible_mask, since sane machines do not suffer from per-cpu ISA
limitations that affect scheduling. The new mask is used when selecting
the fallback runqueue as a last resort before forcing a migration to the
first active CPU.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/mmu_context.h | 14 ++++++++++++++
 kernel/sched/core.c         |  5 ++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index 03dee12d2b61..b9b970f7ab45 100644
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -14,4 +14,18 @@
 static inline void leave_mm(int cpu) { }
 #endif
 
+/*
+ * CPUs that are capable of running user task @p. Must contain at least one
+ * active CPU. It is assumed that the kernel can run on all CPUs, so calling
+ * this for a kernel thread is pointless.
+ *
+ * By default, we assume a sane, homogeneous system.
+ */
+#ifndef task_cpu_possible_mask
+# define task_cpu_possible_mask(p)	cpu_possible_mask
+# define task_cpu_possible(cpu, p)	true
+#else
+# define task_cpu_possible(cpu, p)	cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
+#endif
+
 #endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5226cc26a095..0c1b6f1a6c91 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1814,7 +1814,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
 
 	/* Non kernel threads are not allowed during either online or offline. */
 	if (!(p->flags & PF_KTHREAD))
-		return cpu_active(cpu);
+		return cpu_active(cpu) && task_cpu_possible(cpu, p);
 
 	/* KTHREAD_IS_PER_CPU is always allowed. */
 	if (kthread_is_per_cpu(p))
@@ -2792,10 +2792,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 			 *
 			 * More yuck to audit.
 			 */
-			do_set_cpus_allowed(p, cpu_possible_mask);
+			do_set_cpus_allowed(p, task_cpu_possible_mask(p));
 			state = fail;
 			break;
-
 		case fail:
 			BUG();
 			break;
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 01/16] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection

[Will Deacon]

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

On such a system, we must take care not to migrate a task to an
unsupported CPU when forcefully moving tasks in select_fallback_rq()
in response to a CPU hot-unplug operation.

Introduce a task_cpu_possible_mask() hook which, given a task argument,
allows an architecture to return a cpumask of CPUs that are capable of
executing that task. The default implementation returns the
cpu_possible_mask, since sane machines do not suffer from per-cpu ISA
limitations that affect scheduling. The new mask is used when selecting
the fallback runqueue as a last resort before forcing a migration to the
first active CPU.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/mmu_context.h | 14 ++++++++++++++
 kernel/sched/core.c         |  5 ++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index 03dee12d2b61..b9b970f7ab45 100644
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -14,4 +14,18 @@
 static inline void leave_mm(int cpu) { }
 #endif
 
+/*
+ * CPUs that are capable of running user task @p. Must contain at least one
+ * active CPU. It is assumed that the kernel can run on all CPUs, so calling
+ * this for a kernel thread is pointless.
+ *
+ * By default, we assume a sane, homogeneous system.
+ */
+#ifndef task_cpu_possible_mask
+# define task_cpu_possible_mask(p)	cpu_possible_mask
+# define task_cpu_possible(cpu, p)	true
+#else
+# define task_cpu_possible(cpu, p)	cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
+#endif
+
 #endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5226cc26a095..0c1b6f1a6c91 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1814,7 +1814,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
 
 	/* Non kernel threads are not allowed during either online or offline. */
 	if (!(p->flags & PF_KTHREAD))
-		return cpu_active(cpu);
+		return cpu_active(cpu) && task_cpu_possible(cpu, p);
 
 	/* KTHREAD_IS_PER_CPU is always allowed. */
 	if (kthread_is_per_cpu(p))
@@ -2792,10 +2792,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 			 *
 			 * More yuck to audit.
 			 */
-			do_set_cpus_allowed(p, cpu_possible_mask);
+			do_set_cpus_allowed(p, task_cpu_possible_mask(p));
 			state = fail;
 			break;
-
 		case fail:
 			BUG();
 			break;
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 02/16] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1

[Will Deacon]

If the scheduler cannot find an allowed CPU for a task,
cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask
if cgroup v1 is in use.

In preparation for allowing architectures to provide their own fallback
mask, just return early if we're either using cgroup v1 or we're using
cgroup v2 with a mask that contains invalid CPUs. This will allow
select_fallback_rq() to figure out the mask by itself.

Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/cpuset.h | 1 +
 kernel/cgroup/cpuset.c | 8 ++++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 04c20de66afc..ed6ec677dd6b 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/nodemask.h>
 #include <linux/mm.h>
+#include <linux/mmu_context.h>
 #include <linux/jump_label.h>
 
 #ifdef CONFIG_CPUSETS
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a945504c0ae7..6ec7303d5b1f 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3322,9 +3322,13 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 
 void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
+	const struct cpumask *cs_mask;
+	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+
 	rcu_read_lock();
-	do_set_cpus_allowed(tsk, is_in_v2_mode() ?
-		task_cs(tsk)->cpus_allowed : cpu_possible_mask);
+	cs_mask = task_cs(tsk)->cpus_allowed;
+	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask))
+		do_set_cpus_allowed(tsk, cs_mask);
 	rcu_read_unlock();
 
 	/*
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 02/16] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1

[Will Deacon]

If the scheduler cannot find an allowed CPU for a task,
cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask
if cgroup v1 is in use.

In preparation for allowing architectures to provide their own fallback
mask, just return early if we're either using cgroup v1 or we're using
cgroup v2 with a mask that contains invalid CPUs. This will allow
select_fallback_rq() to figure out the mask by itself.

Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/cpuset.h | 1 +
 kernel/cgroup/cpuset.c | 8 ++++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 04c20de66afc..ed6ec677dd6b 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/nodemask.h>
 #include <linux/mm.h>
+#include <linux/mmu_context.h>
 #include <linux/jump_label.h>
 
 #ifdef CONFIG_CPUSETS
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a945504c0ae7..6ec7303d5b1f 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3322,9 +3322,13 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 
 void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
+	const struct cpumask *cs_mask;
+	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+
 	rcu_read_lock();
-	do_set_cpus_allowed(tsk, is_in_v2_mode() ?
-		task_cs(tsk)->cpus_allowed : cpu_possible_mask);
+	cs_mask = task_cs(tsk)->cpus_allowed;
+	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask))
+		do_set_cpus_allowed(tsk, cs_mask);
 	rcu_read_unlock();
 
 	/*
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 03/16] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()

[Will Deacon]

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

Modify guarantee_online_cpus() to take task_cpu_possible_mask() into
account when trying to find a suitable set of online CPUs for a given
task. This will avoid passing an invalid mask to set_cpus_allowed_ptr()
during ->attach() and will subsequently allow the cpuset hierarchy to be
taken into account when forcefully overriding the affinity mask for a
task which requires migration to a compatible CPU.

Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/cpuset.h |  2 +-
 kernel/cgroup/cpuset.c | 43 +++++++++++++++++++++++++-----------------
 2 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index ed6ec677dd6b..414a8e694413 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { }
 static inline void cpuset_cpus_allowed(struct task_struct *p,
 				       struct cpumask *mask)
 {
-	cpumask_copy(mask, cpu_possible_mask);
+	cpumask_copy(mask, task_cpu_possible_mask(p));
 }
 
 static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 6ec7303d5b1f..4e7c271e3800 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -372,18 +372,29 @@ static inline bool is_in_v2_mode(void)
 }
 
 /*
- * Return in pmask the portion of a cpusets's cpus_allowed that
- * are online.  If none are online, walk up the cpuset hierarchy
- * until we find one that does have some online cpus.
+ * Return in pmask the portion of a task's cpusets's cpus_allowed that
+ * are online and are capable of running the task.  If none are found,
+ * walk up the cpuset hierarchy until we find one that does have some
+ * appropriate cpus.
  *
  * One way or another, we guarantee to return some non-empty subset
  * of cpu_online_mask.
  *
  * Call with callback_lock or cpuset_mutex held.
  */
-static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
+static void guarantee_online_cpus(struct task_struct *tsk,
+				  struct cpumask *pmask)
 {
-	while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) {
+	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+	struct cpuset *cs;
+
+	if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask)))
+		cpumask_copy(pmask, cpu_online_mask);
+
+	rcu_read_lock();
+	cs = task_cs(tsk);
+
+	while (!cpumask_intersects(cs->effective_cpus, pmask)) {
 		cs = parent_cs(cs);
 		if (unlikely(!cs)) {
 			/*
@@ -393,11 +404,13 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
 			 * cpuset's effective_cpus is on its way to be
 			 * identical to cpu_online_mask.
 			 */
-			cpumask_copy(pmask, cpu_online_mask);
-			return;
+			goto out_unlock;
 		}
 	}
-	cpumask_and(pmask, cs->effective_cpus, cpu_online_mask);
+	cpumask_and(pmask, pmask, cs->effective_cpus);
+
+out_unlock:
+	rcu_read_unlock();
 }
 
 /*
@@ -2199,15 +2212,13 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 
 	percpu_down_write(&cpuset_rwsem);
 
-	/* prepare for attach */
-	if (cs == &top_cpuset)
-		cpumask_copy(cpus_attach, cpu_possible_mask);
-	else
-		guarantee_online_cpus(cs, cpus_attach);
-
 	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
 
 	cgroup_taskset_for_each(task, css, tset) {
+		if (cs != &top_cpuset)
+			guarantee_online_cpus(task, cpus_attach);
+		else
+			cpumask_copy(cpus_attach, task_cpu_possible_mask(task));
 		/*
 		 * can_attach beforehand should guarantee that this doesn't
 		 * fail.  TODO: have a better way to handle failure here
@@ -3302,9 +3313,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 	unsigned long flags;
 
 	spin_lock_irqsave(&callback_lock, flags);
-	rcu_read_lock();
-	guarantee_online_cpus(task_cs(tsk), pmask);
-	rcu_read_unlock();
+	guarantee_online_cpus(tsk, pmask);
 	spin_unlock_irqrestore(&callback_lock, flags);
 }
 
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 03/16] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()

[Will Deacon]

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

Modify guarantee_online_cpus() to take task_cpu_possible_mask() into
account when trying to find a suitable set of online CPUs for a given
task. This will avoid passing an invalid mask to set_cpus_allowed_ptr()
during ->attach() and will subsequently allow the cpuset hierarchy to be
taken into account when forcefully overriding the affinity mask for a
task which requires migration to a compatible CPU.

Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/cpuset.h |  2 +-
 kernel/cgroup/cpuset.c | 43 +++++++++++++++++++++++++-----------------
 2 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index ed6ec677dd6b..414a8e694413 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { }
 static inline void cpuset_cpus_allowed(struct task_struct *p,
 				       struct cpumask *mask)
 {
-	cpumask_copy(mask, cpu_possible_mask);
+	cpumask_copy(mask, task_cpu_possible_mask(p));
 }
 
 static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 6ec7303d5b1f..4e7c271e3800 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -372,18 +372,29 @@ static inline bool is_in_v2_mode(void)
 }
 
 /*
- * Return in pmask the portion of a cpusets's cpus_allowed that
- * are online.  If none are online, walk up the cpuset hierarchy
- * until we find one that does have some online cpus.
+ * Return in pmask the portion of a task's cpusets's cpus_allowed that
+ * are online and are capable of running the task.  If none are found,
+ * walk up the cpuset hierarchy until we find one that does have some
+ * appropriate cpus.
  *
  * One way or another, we guarantee to return some non-empty subset
  * of cpu_online_mask.
  *
  * Call with callback_lock or cpuset_mutex held.
  */
-static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
+static void guarantee_online_cpus(struct task_struct *tsk,
+				  struct cpumask *pmask)
 {
-	while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) {
+	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+	struct cpuset *cs;
+
+	if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask)))
+		cpumask_copy(pmask, cpu_online_mask);
+
+	rcu_read_lock();
+	cs = task_cs(tsk);
+
+	while (!cpumask_intersects(cs->effective_cpus, pmask)) {
 		cs = parent_cs(cs);
 		if (unlikely(!cs)) {
 			/*
@@ -393,11 +404,13 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
 			 * cpuset's effective_cpus is on its way to be
 			 * identical to cpu_online_mask.
 			 */
-			cpumask_copy(pmask, cpu_online_mask);
-			return;
+			goto out_unlock;
 		}
 	}
-	cpumask_and(pmask, cs->effective_cpus, cpu_online_mask);
+	cpumask_and(pmask, pmask, cs->effective_cpus);
+
+out_unlock:
+	rcu_read_unlock();
 }
 
 /*
@@ -2199,15 +2212,13 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 
 	percpu_down_write(&cpuset_rwsem);
 
-	/* prepare for attach */
-	if (cs == &top_cpuset)
-		cpumask_copy(cpus_attach, cpu_possible_mask);
-	else
-		guarantee_online_cpus(cs, cpus_attach);
-
 	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
 
 	cgroup_taskset_for_each(task, css, tset) {
+		if (cs != &top_cpuset)
+			guarantee_online_cpus(task, cpus_attach);
+		else
+			cpumask_copy(cpus_attach, task_cpu_possible_mask(task));
 		/*
 		 * can_attach beforehand should guarantee that this doesn't
 		 * fail.  TODO: have a better way to handle failure here
@@ -3302,9 +3313,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 	unsigned long flags;
 
 	spin_lock_irqsave(&callback_lock, flags);
-	rcu_read_lock();
-	guarantee_online_cpus(task_cs(tsk), pmask);
-	rcu_read_unlock();
+	guarantee_online_cpus(tsk, pmask);
 	spin_unlock_irqrestore(&callback_lock, flags);
 }
 
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 04/16] cpuset: Cleanup cpuset_cpus_allowed_fallback() use in select_fallback_rq()

[Will Deacon]

select_fallback_rq() only needs to recheck for an allowed CPU if the
affinity mask of the task has changed since the last check.

Return a 'bool' from cpuset_cpus_allowed_fallback() to indicate whether
the affinity mask was updated, and use this to elide the allowed check
when the mask has been left alone.

No functional change.

Suggested-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/cpuset.h |  5 +++--
 kernel/cgroup/cpuset.c | 10 ++++++++--
 kernel/sched/core.c    |  3 +--
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 414a8e694413..d2b9c41c8edf 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -59,7 +59,7 @@ extern void cpuset_wait_for_hotplug(void);
 extern void cpuset_read_lock(void);
 extern void cpuset_read_unlock(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
-extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
+extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
@@ -188,8 +188,9 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,
 	cpumask_copy(mask, task_cpu_possible_mask(p));
 }
 
-static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
+static inline bool cpuset_cpus_allowed_fallback(struct task_struct *p)
 {
+	return false;
 }
 
 static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 4e7c271e3800..a6bab2259f98 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3327,17 +3327,22 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
  * which will not contain a sane cpumask during cases such as cpu hotplugging.
  * This is the absolute last resort for the scheduler and it is only used if
  * _every_ other avenue has been traveled.
+ *
+ * Returns true if the affinity of @tsk was changed, false otherwise.
  **/
 
-void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
+bool cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
 	const struct cpumask *cs_mask;
+	bool changed = false;
 	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
 
 	rcu_read_lock();
 	cs_mask = task_cs(tsk)->cpus_allowed;
-	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask))
+	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask)) {
 		do_set_cpus_allowed(tsk, cs_mask);
+		changed = true;
+	}
 	rcu_read_unlock();
 
 	/*
@@ -3357,6 +3362,7 @@ void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 	 * select_fallback_rq() will fix things ups and set cpu_possible_mask
 	 * if required.
 	 */
+	return changed;
 }
 
 void __init cpuset_init_current_mems_allowed(void)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0c1b6f1a6c91..9e75cb3fbc9c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2779,8 +2779,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 		/* No more Mr. Nice Guy. */
 		switch (state) {
 		case cpuset:
-			if (IS_ENABLED(CONFIG_CPUSETS)) {
-				cpuset_cpus_allowed_fallback(p);
+			if (cpuset_cpus_allowed_fallback(p)) {
 				state = possible;
 				break;
 			}
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 04/16] cpuset: Cleanup cpuset_cpus_allowed_fallback() use in select_fallback_rq()

[Will Deacon]

select_fallback_rq() only needs to recheck for an allowed CPU if the
affinity mask of the task has changed since the last check.

Return a 'bool' from cpuset_cpus_allowed_fallback() to indicate whether
the affinity mask was updated, and use this to elide the allowed check
when the mask has been left alone.

No functional change.

Suggested-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/cpuset.h |  5 +++--
 kernel/cgroup/cpuset.c | 10 ++++++++--
 kernel/sched/core.c    |  3 +--
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 414a8e694413..d2b9c41c8edf 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -59,7 +59,7 @@ extern void cpuset_wait_for_hotplug(void);
 extern void cpuset_read_lock(void);
 extern void cpuset_read_unlock(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
-extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
+extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
@@ -188,8 +188,9 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,
 	cpumask_copy(mask, task_cpu_possible_mask(p));
 }
 
-static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
+static inline bool cpuset_cpus_allowed_fallback(struct task_struct *p)
 {
+	return false;
 }
 
 static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 4e7c271e3800..a6bab2259f98 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3327,17 +3327,22 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
  * which will not contain a sane cpumask during cases such as cpu hotplugging.
  * This is the absolute last resort for the scheduler and it is only used if
  * _every_ other avenue has been traveled.
+ *
+ * Returns true if the affinity of @tsk was changed, false otherwise.
  **/
 
-void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
+bool cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
 	const struct cpumask *cs_mask;
+	bool changed = false;
 	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
 
 	rcu_read_lock();
 	cs_mask = task_cs(tsk)->cpus_allowed;
-	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask))
+	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask)) {
 		do_set_cpus_allowed(tsk, cs_mask);
+		changed = true;
+	}
 	rcu_read_unlock();
 
 	/*
@@ -3357,6 +3362,7 @@ void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 	 * select_fallback_rq() will fix things ups and set cpu_possible_mask
 	 * if required.
 	 */
+	return changed;
 }
 
 void __init cpuset_init_current_mems_allowed(void)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0c1b6f1a6c91..9e75cb3fbc9c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2779,8 +2779,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 		/* No more Mr. Nice Guy. */
 		switch (state) {
 		case cpuset:
-			if (IS_ENABLED(CONFIG_CPUSETS)) {
-				cpuset_cpus_allowed_fallback(p);
+			if (cpuset_cpus_allowed_fallback(p)) {
 				state = possible;
 				break;
 			}
-- 
2.32.0.93.g670b81a890-goog


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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 05/16] sched: Reject CPU affinity changes based on task_cpu_possible_mask()

[Will Deacon]

Reject explicit requests to change the affinity mask of a task via
set_cpus_allowed_ptr() if the requested mask is not a subset of the
mask returned by task_cpu_possible_mask(). This ensures that the
'cpus_mask' for a given task cannot contain CPUs which are incapable of
executing it, except in cases where the affinity is forced.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 kernel/sched/core.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9e75cb3fbc9c..09fe20b3d6bb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2347,15 +2347,17 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 				  u32 flags)
 {
 	const struct cpumask *cpu_valid_mask = cpu_active_mask;
+	const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
 	unsigned int dest_cpu;
 	struct rq_flags rf;
 	struct rq *rq;
 	int ret = 0;
+	bool kthread = p->flags & PF_KTHREAD;
 
 	rq = task_rq_lock(p, &rf);
 	update_rq_clock(rq);
 
-	if (p->flags & PF_KTHREAD || is_migration_disabled(p)) {
+	if (kthread || is_migration_disabled(p)) {
 		/*
 		 * Kernel threads are allowed on online && !active CPUs,
 		 * however, during cpu-hot-unplug, even these might get pushed
@@ -2369,6 +2371,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 		cpu_valid_mask = cpu_online_mask;
 	}
 
+	if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	/*
 	 * Must re-check here, to close a race against __kthread_bind(),
 	 * sched_setaffinity() is not guaranteed to observe the flag.
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 05/16] sched: Reject CPU affinity changes based on task_cpu_possible_mask()

[Will Deacon]

Reject explicit requests to change the affinity mask of a task via
set_cpus_allowed_ptr() if the requested mask is not a subset of the
mask returned by task_cpu_possible_mask(). This ensures that the
'cpus_mask' for a given task cannot contain CPUs which are incapable of
executing it, except in cases where the affinity is forced.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 kernel/sched/core.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9e75cb3fbc9c..09fe20b3d6bb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2347,15 +2347,17 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 				  u32 flags)
 {
 	const struct cpumask *cpu_valid_mask = cpu_active_mask;
+	const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
 	unsigned int dest_cpu;
 	struct rq_flags rf;
 	struct rq *rq;
 	int ret = 0;
+	bool kthread = p->flags & PF_KTHREAD;
 
 	rq = task_rq_lock(p, &rf);
 	update_rq_clock(rq);
 
-	if (p->flags & PF_KTHREAD || is_migration_disabled(p)) {
+	if (kthread || is_migration_disabled(p)) {
 		/*
 		 * Kernel threads are allowed on online && !active CPUs,
 		 * however, during cpu-hot-unplug, even these might get pushed
@@ -2369,6 +2371,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 		cpu_valid_mask = cpu_online_mask;
 	}
 
+	if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	/*
 	 * Must re-check here, to close a race against __kthread_bind(),
 	 * sched_setaffinity() is not guaranteed to observe the flag.
-- 
2.32.0.93.g670b81a890-goog


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[PATCH v10 06/16] sched: Introduce task_struct::user_cpus_ptr to track requested affinity

[Will Deacon]

In preparation for saving and restoring the user-requested CPU affinity
mask of a task, add a new cpumask_t pointer to 'struct task_struct'.

If the pointer is non-NULL, then the mask is copied across fork() and
freed on task exit.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/sched.h | 13 +++++++++++++
 init/init_task.c      |  1 +
 kernel/fork.c         |  2 ++
 kernel/sched/core.c   | 20 ++++++++++++++++++++
 4 files changed, 36 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d2c881384517..db32d4f7e5b3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -730,6 +730,7 @@ struct task_struct {
 	unsigned int			policy;
 	int				nr_cpus_allowed;
 	const cpumask_t			*cpus_ptr;
+	cpumask_t			*user_cpus_ptr;
 	cpumask_t			cpus_mask;
 	void				*migration_pending;
 #ifdef CONFIG_SMP
@@ -1688,6 +1689,8 @@ extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_
 #ifdef CONFIG_SMP
 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
+extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
+extern void release_user_cpus_ptr(struct task_struct *p);
 #else
 static inline void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
@@ -1698,6 +1701,16 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p, const struct cpuma
 		return -EINVAL;
 	return 0;
 }
+static inline int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node)
+{
+	if (src->user_cpus_ptr)
+		return -EINVAL;
+	return 0;
+}
+static inline void release_user_cpus_ptr(struct task_struct *p)
+{
+	WARN_ON(p->user_cpus_ptr);
+}
 #endif
 
 extern int yield_to(struct task_struct *p, bool preempt);
diff --git a/init/init_task.c b/init/init_task.c
index 8b08c2e19cbb..158c2b1689e1 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -80,6 +80,7 @@ struct task_struct init_task
 	.normal_prio	= MAX_PRIO - 20,
 	.policy		= SCHED_NORMAL,
 	.cpus_ptr	= &init_task.cpus_mask,
+	.user_cpus_ptr	= NULL,
 	.cpus_mask	= CPU_MASK_ALL,
 	.nr_cpus_allowed= NR_CPUS,
 	.mm		= NULL,
diff --git a/kernel/fork.c b/kernel/fork.c
index dc06afd725cb..d3710e7f1686 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -446,6 +446,7 @@ void put_task_stack(struct task_struct *tsk)
 
 void free_task(struct task_struct *tsk)
 {
+	release_user_cpus_ptr(tsk);
 	scs_release(tsk);
 
 #ifndef CONFIG_THREAD_INFO_IN_TASK
@@ -918,6 +919,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 #endif
 	if (orig->cpus_ptr == &orig->cpus_mask)
 		tsk->cpus_ptr = &tsk->cpus_mask;
+	dup_user_cpus_ptr(tsk, orig, node);
 
 	/*
 	 * One for the user space visible state that goes away when reaped.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 09fe20b3d6bb..f6ea3d7a07f2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2126,6 +2126,26 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 	__do_set_cpus_allowed(p, new_mask, 0);
 }
 
+int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
+		      int node)
+{
+	if (!src->user_cpus_ptr)
+		return 0;
+
+	dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
+	if (!dst->user_cpus_ptr)
+		return -ENOMEM;
+
+	cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
+	return 0;
+}
+
+void release_user_cpus_ptr(struct task_struct *p)
+{
+	kfree(p->user_cpus_ptr);
+	p->user_cpus_ptr = NULL;
+}
+
 /*
  * This function is wildly self concurrent; here be dragons.
  *
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 06/16] sched: Introduce task_struct::user_cpus_ptr to track requested affinity

[Will Deacon]

In preparation for saving and restoring the user-requested CPU affinity
mask of a task, add a new cpumask_t pointer to 'struct task_struct'.

If the pointer is non-NULL, then the mask is copied across fork() and
freed on task exit.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/sched.h | 13 +++++++++++++
 init/init_task.c      |  1 +
 kernel/fork.c         |  2 ++
 kernel/sched/core.c   | 20 ++++++++++++++++++++
 4 files changed, 36 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d2c881384517..db32d4f7e5b3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -730,6 +730,7 @@ struct task_struct {
 	unsigned int			policy;
 	int				nr_cpus_allowed;
 	const cpumask_t			*cpus_ptr;
+	cpumask_t			*user_cpus_ptr;
 	cpumask_t			cpus_mask;
 	void				*migration_pending;
 #ifdef CONFIG_SMP
@@ -1688,6 +1689,8 @@ extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_
 #ifdef CONFIG_SMP
 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
+extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
+extern void release_user_cpus_ptr(struct task_struct *p);
 #else
 static inline void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
@@ -1698,6 +1701,16 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p, const struct cpuma
 		return -EINVAL;
 	return 0;
 }
+static inline int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node)
+{
+	if (src->user_cpus_ptr)
+		return -EINVAL;
+	return 0;
+}
+static inline void release_user_cpus_ptr(struct task_struct *p)
+{
+	WARN_ON(p->user_cpus_ptr);
+}
 #endif
 
 extern int yield_to(struct task_struct *p, bool preempt);
diff --git a/init/init_task.c b/init/init_task.c
index 8b08c2e19cbb..158c2b1689e1 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -80,6 +80,7 @@ struct task_struct init_task
 	.normal_prio	= MAX_PRIO - 20,
 	.policy		= SCHED_NORMAL,
 	.cpus_ptr	= &init_task.cpus_mask,
+	.user_cpus_ptr	= NULL,
 	.cpus_mask	= CPU_MASK_ALL,
 	.nr_cpus_allowed= NR_CPUS,
 	.mm		= NULL,
diff --git a/kernel/fork.c b/kernel/fork.c
index dc06afd725cb..d3710e7f1686 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -446,6 +446,7 @@ void put_task_stack(struct task_struct *tsk)
 
 void free_task(struct task_struct *tsk)
 {
+	release_user_cpus_ptr(tsk);
 	scs_release(tsk);
 
 #ifndef CONFIG_THREAD_INFO_IN_TASK
@@ -918,6 +919,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 #endif
 	if (orig->cpus_ptr == &orig->cpus_mask)
 		tsk->cpus_ptr = &tsk->cpus_mask;
+	dup_user_cpus_ptr(tsk, orig, node);
 
 	/*
 	 * One for the user space visible state that goes away when reaped.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 09fe20b3d6bb..f6ea3d7a07f2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2126,6 +2126,26 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 	__do_set_cpus_allowed(p, new_mask, 0);
 }
 
+int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
+		      int node)
+{
+	if (!src->user_cpus_ptr)
+		return 0;
+
+	dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
+	if (!dst->user_cpus_ptr)
+		return -ENOMEM;
+
+	cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
+	return 0;
+}
+
+void release_user_cpus_ptr(struct task_struct *p)
+{
+	kfree(p->user_cpus_ptr);
+	p->user_cpus_ptr = NULL;
+}
+
 /*
  * This function is wildly self concurrent; here be dragons.
  *
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 07/16] sched: Split the guts of sched_setaffinity() into a helper function

[Will Deacon]

In preparation for replaying user affinity requests using a saved mask,
split sched_setaffinity() up so that the initial task lookup and
security checks are only performed when the request is coming directly
from userspace.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 kernel/sched/core.c | 105 ++++++++++++++++++++++++--------------------
 1 file changed, 57 insertions(+), 48 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f6ea3d7a07f2..d151446d5987 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6787,53 +6787,22 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	return retval;
 }
 
-long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
+static int
+__sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 {
-	cpumask_var_t cpus_allowed, new_mask;
-	struct task_struct *p;
 	int retval;
+	cpumask_var_t cpus_allowed, new_mask;
 
-	rcu_read_lock();
-
-	p = find_process_by_pid(pid);
-	if (!p) {
-		rcu_read_unlock();
-		return -ESRCH;
-	}
-
-	/* Prevent p going away */
-	get_task_struct(p);
-	rcu_read_unlock();
+	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL))
+		return -ENOMEM;
 
-	if (p->flags & PF_NO_SETAFFINITY) {
-		retval = -EINVAL;
-		goto out_put_task;
-	}
-	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
-		retval = -ENOMEM;
-		goto out_put_task;
-	}
 	if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
 		retval = -ENOMEM;
 		goto out_free_cpus_allowed;
 	}
-	retval = -EPERM;
-	if (!check_same_owner(p)) {
-		rcu_read_lock();
-		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
-			rcu_read_unlock();
-			goto out_free_new_mask;
-		}
-		rcu_read_unlock();
-	}
-
-	retval = security_task_setscheduler(p);
-	if (retval)
-		goto out_free_new_mask;
-
 
 	cpuset_cpus_allowed(p, cpus_allowed);
-	cpumask_and(new_mask, in_mask, cpus_allowed);
+	cpumask_and(new_mask, mask, cpus_allowed);
 
 	/*
 	 * Since bandwidth control happens on root_domain basis,
@@ -6854,23 +6823,63 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
 #endif
 again:
 	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK);
+	if (retval)
+		goto out_free_new_mask;
 
-	if (!retval) {
-		cpuset_cpus_allowed(p, cpus_allowed);
-		if (!cpumask_subset(new_mask, cpus_allowed)) {
-			/*
-			 * We must have raced with a concurrent cpuset
-			 * update. Just reset the cpus_allowed to the
-			 * cpuset's cpus_allowed
-			 */
-			cpumask_copy(new_mask, cpus_allowed);
-			goto again;
-		}
+	cpuset_cpus_allowed(p, cpus_allowed);
+	if (!cpumask_subset(new_mask, cpus_allowed)) {
+		/*
+		 * We must have raced with a concurrent cpuset update.
+		 * Just reset the cpumask to the cpuset's cpus_allowed.
+		 */
+		cpumask_copy(new_mask, cpus_allowed);
+		goto again;
 	}
+
 out_free_new_mask:
 	free_cpumask_var(new_mask);
 out_free_cpus_allowed:
 	free_cpumask_var(cpus_allowed);
+	return retval;
+}
+
+long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
+{
+	struct task_struct *p;
+	int retval;
+
+	rcu_read_lock();
+
+	p = find_process_by_pid(pid);
+	if (!p) {
+		rcu_read_unlock();
+		return -ESRCH;
+	}
+
+	/* Prevent p going away */
+	get_task_struct(p);
+	rcu_read_unlock();
+
+	if (p->flags & PF_NO_SETAFFINITY) {
+		retval = -EINVAL;
+		goto out_put_task;
+	}
+
+	if (!check_same_owner(p)) {
+		rcu_read_lock();
+		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
+			rcu_read_unlock();
+			retval = -EPERM;
+			goto out_put_task;
+		}
+		rcu_read_unlock();
+	}
+
+	retval = security_task_setscheduler(p);
+	if (retval)
+		goto out_put_task;
+
+	retval = __sched_setaffinity(p, in_mask);
 out_put_task:
 	put_task_struct(p);
 	return retval;
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 07/16] sched: Split the guts of sched_setaffinity() into a helper function

[Will Deacon]

In preparation for replaying user affinity requests using a saved mask,
split sched_setaffinity() up so that the initial task lookup and
security checks are only performed when the request is coming directly
from userspace.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 kernel/sched/core.c | 105 ++++++++++++++++++++++++--------------------
 1 file changed, 57 insertions(+), 48 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f6ea3d7a07f2..d151446d5987 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6787,53 +6787,22 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	return retval;
 }
 
-long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
+static int
+__sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 {
-	cpumask_var_t cpus_allowed, new_mask;
-	struct task_struct *p;
 	int retval;
+	cpumask_var_t cpus_allowed, new_mask;
 
-	rcu_read_lock();
-
-	p = find_process_by_pid(pid);
-	if (!p) {
-		rcu_read_unlock();
-		return -ESRCH;
-	}
-
-	/* Prevent p going away */
-	get_task_struct(p);
-	rcu_read_unlock();
+	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL))
+		return -ENOMEM;
 
-	if (p->flags & PF_NO_SETAFFINITY) {
-		retval = -EINVAL;
-		goto out_put_task;
-	}
-	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
-		retval = -ENOMEM;
-		goto out_put_task;
-	}
 	if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
 		retval = -ENOMEM;
 		goto out_free_cpus_allowed;
 	}
-	retval = -EPERM;
-	if (!check_same_owner(p)) {
-		rcu_read_lock();
-		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
-			rcu_read_unlock();
-			goto out_free_new_mask;
-		}
-		rcu_read_unlock();
-	}
-
-	retval = security_task_setscheduler(p);
-	if (retval)
-		goto out_free_new_mask;
-
 
 	cpuset_cpus_allowed(p, cpus_allowed);
-	cpumask_and(new_mask, in_mask, cpus_allowed);
+	cpumask_and(new_mask, mask, cpus_allowed);
 
 	/*
 	 * Since bandwidth control happens on root_domain basis,
@@ -6854,23 +6823,63 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
 #endif
 again:
 	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK);
+	if (retval)
+		goto out_free_new_mask;
 
-	if (!retval) {
-		cpuset_cpus_allowed(p, cpus_allowed);
-		if (!cpumask_subset(new_mask, cpus_allowed)) {
-			/*
-			 * We must have raced with a concurrent cpuset
-			 * update. Just reset the cpus_allowed to the
-			 * cpuset's cpus_allowed
-			 */
-			cpumask_copy(new_mask, cpus_allowed);
-			goto again;
-		}
+	cpuset_cpus_allowed(p, cpus_allowed);
+	if (!cpumask_subset(new_mask, cpus_allowed)) {
+		/*
+		 * We must have raced with a concurrent cpuset update.
+		 * Just reset the cpumask to the cpuset's cpus_allowed.
+		 */
+		cpumask_copy(new_mask, cpus_allowed);
+		goto again;
 	}
+
 out_free_new_mask:
 	free_cpumask_var(new_mask);
 out_free_cpus_allowed:
 	free_cpumask_var(cpus_allowed);
+	return retval;
+}
+
+long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
+{
+	struct task_struct *p;
+	int retval;
+
+	rcu_read_lock();
+
+	p = find_process_by_pid(pid);
+	if (!p) {
+		rcu_read_unlock();
+		return -ESRCH;
+	}
+
+	/* Prevent p going away */
+	get_task_struct(p);
+	rcu_read_unlock();
+
+	if (p->flags & PF_NO_SETAFFINITY) {
+		retval = -EINVAL;
+		goto out_put_task;
+	}
+
+	if (!check_same_owner(p)) {
+		rcu_read_lock();
+		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
+			rcu_read_unlock();
+			retval = -EPERM;
+			goto out_put_task;
+		}
+		rcu_read_unlock();
+	}
+
+	retval = security_task_setscheduler(p);
+	if (retval)
+		goto out_put_task;
+
+	retval = __sched_setaffinity(p, in_mask);
 out_put_task:
 	put_task_struct(p);
 	return retval;
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 08/16] sched: Allow task CPU affinity to be restricted on asymmetric systems

[Will Deacon]

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

Although userspace can carefully manage the affinity masks for such
tasks, one place where it is particularly problematic is execve()
because the CPU on which the execve() is occurring may be incompatible
with the new application image. In such a situation, it is desirable to
restrict the affinity mask of the task and ensure that the new image is
entered on a compatible CPU. From userspace's point of view, this looks
the same as if the incompatible CPUs have been hotplugged off in the
task's affinity mask. Similarly, if a subsequent execve() reverts to
a compatible image, then the old affinity is restored if it is still
valid.

In preparation for restricting the affinity mask for compat tasks on
arm64 systems without uniform support for 32-bit applications, introduce
{force,relax}_compatible_cpus_allowed_ptr(), which respectively restrict
and restore the affinity mask for a task based on the compatible CPUs.

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/sched.h |   2 +
 kernel/sched/core.c   | 180 ++++++++++++++++++++++++++++++++++++++----
 kernel/sched/sched.h  |   1 +
 3 files changed, 167 insertions(+), 16 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index db32d4f7e5b3..91a6cfeae242 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1691,6 +1691,8 @@ extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
 extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
 extern void release_user_cpus_ptr(struct task_struct *p);
+extern void force_compatible_cpus_allowed_ptr(struct task_struct *p);
+extern void relax_compatible_cpus_allowed_ptr(struct task_struct *p);
 #else
 static inline void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d151446d5987..d3d5e8b33961 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2354,27 +2354,22 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
 }
 
 /*
- * Change a given task's CPU affinity. Migrate the thread to a
- * proper CPU and schedule it away if the CPU it's executing on
- * is removed from the allowed bitmask.
- *
- * NOTE: the caller must have a valid reference to the task, the
- * task must not exit() & deallocate itself prematurely. The
- * call is not atomic; no spinlocks may be held.
+ * Called with both p->pi_lock and rq->lock held; drops both before returning.
  */
-static int __set_cpus_allowed_ptr(struct task_struct *p,
-				  const struct cpumask *new_mask,
-				  u32 flags)
+static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
+					 const struct cpumask *new_mask,
+					 u32 flags,
+					 struct rq *rq,
+					 struct rq_flags *rf)
+	__releases(rq->lock)
+	__releases(p->pi_lock)
 {
 	const struct cpumask *cpu_valid_mask = cpu_active_mask;
 	const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
 	unsigned int dest_cpu;
-	struct rq_flags rf;
-	struct rq *rq;
 	int ret = 0;
 	bool kthread = p->flags & PF_KTHREAD;
 
-	rq = task_rq_lock(p, &rf);
 	update_rq_clock(rq);
 
 	if (kthread || is_migration_disabled(p)) {
@@ -2430,20 +2425,173 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 
 	__do_set_cpus_allowed(p, new_mask, flags);
 
-	return affine_move_task(rq, p, &rf, dest_cpu, flags);
+	if (flags & SCA_USER)
+		release_user_cpus_ptr(p);
+
+	return affine_move_task(rq, p, rf, dest_cpu, flags);
 
 out:
-	task_rq_unlock(rq, p, &rf);
+	task_rq_unlock(rq, p, rf);
 
 	return ret;
 }
 
+/*
+ * Change a given task's CPU affinity. Migrate the thread to a
+ * proper CPU and schedule it away if the CPU it's executing on
+ * is removed from the allowed bitmask.
+ *
+ * NOTE: the caller must have a valid reference to the task, the
+ * task must not exit() & deallocate itself prematurely. The
+ * call is not atomic; no spinlocks may be held.
+ */
+static int __set_cpus_allowed_ptr(struct task_struct *p,
+				  const struct cpumask *new_mask, u32 flags)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+
+	rq = task_rq_lock(p, &rf);
+	return __set_cpus_allowed_ptr_locked(p, new_mask, flags, rq, &rf);
+}
+
 int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 {
 	return __set_cpus_allowed_ptr(p, new_mask, 0);
 }
 EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
 
+/*
+ * Change a given task's CPU affinity to the intersection of its current
+ * affinity mask and @subset_mask, writing the resulting mask to @new_mask
+ * and pointing @p->user_cpus_ptr to a copy of the old mask.
+ * If the resulting mask is empty, leave the affinity unchanged and return
+ * -EINVAL.
+ */
+static int restrict_cpus_allowed_ptr(struct task_struct *p,
+				     struct cpumask *new_mask,
+				     const struct cpumask *subset_mask)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+	int err;
+	struct cpumask *user_mask = NULL;
+
+	if (!p->user_cpus_ptr) {
+		user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
+
+		if (!user_mask)
+			return -ENOMEM;
+	}
+
+	rq = task_rq_lock(p, &rf);
+
+	/*
+	 * Forcefully restricting the affinity of a deadline task is
+	 * likely to cause problems, so fail and noisily override the
+	 * mask entirely.
+	 */
+	if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
+		err = -EPERM;
+		goto err_unlock;
+	}
+
+	if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
+		err = -EINVAL;
+		goto err_unlock;
+	}
+
+	/*
+	 * We're about to butcher the task affinity, so keep track of what
+	 * the user asked for in case we're able to restore it later on.
+	 */
+	if (user_mask) {
+		cpumask_copy(user_mask, p->cpus_ptr);
+		p->user_cpus_ptr = user_mask;
+	}
+
+	return __set_cpus_allowed_ptr_locked(p, new_mask, 0, rq, &rf);
+
+err_unlock:
+	task_rq_unlock(rq, p, &rf);
+	kfree(user_mask);
+	return err;
+}
+
+/*
+ * Restrict the CPU affinity of task @p so that it is a subset of
+ * task_cpu_possible_mask() and point @p->user_cpu_ptr to a copy of the
+ * old affinity mask. If the resulting mask is empty, we warn and walk
+ * up the cpuset hierarchy until we find a suitable mask.
+ */
+void force_compatible_cpus_allowed_ptr(struct task_struct *p)
+{
+	cpumask_var_t new_mask;
+	const struct cpumask *override_mask = task_cpu_possible_mask(p);
+
+	alloc_cpumask_var(&new_mask, GFP_KERNEL);
+
+	/*
+	 * __migrate_task() can fail silently in the face of concurrent
+	 * offlining of the chosen destination CPU, so take the hotplug
+	 * lock to ensure that the migration succeeds.
+	 */
+	cpus_read_lock();
+	if (!cpumask_available(new_mask))
+		goto out_set_mask;
+
+	if (!restrict_cpus_allowed_ptr(p, new_mask, override_mask))
+		goto out_free_mask;
+
+	/*
+	 * We failed to find a valid subset of the affinity mask for the
+	 * task, so override it based on its cpuset hierarchy.
+	 */
+	cpuset_cpus_allowed(p, new_mask);
+	override_mask = new_mask;
+
+out_set_mask:
+	if (printk_ratelimit()) {
+		printk_deferred("Overriding affinity for process %d (%s) to CPUs %*pbl\n",
+				task_pid_nr(p), p->comm,
+				cpumask_pr_args(override_mask));
+	}
+
+	WARN_ON(set_cpus_allowed_ptr(p, override_mask));
+out_free_mask:
+	cpus_read_unlock();
+	free_cpumask_var(new_mask);
+}
+
+static int
+__sched_setaffinity(struct task_struct *p, const struct cpumask *mask);
+
+/*
+ * Restore the affinity of a task @p which was previously restricted by a
+ * call to force_compatible_cpus_allowed_ptr(). This will clear (and free)
+ * @p->user_cpus_ptr.
+ *
+ * It is the caller's responsibility to serialise this with any calls to
+ * force_compatible_cpus_allowed_ptr(@p).
+ */
+void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
+{
+	unsigned long flags;
+	struct cpumask *mask = p->user_cpus_ptr;
+
+	/*
+	 * Try to restore the old affinity mask. If this fails, then
+	 * we free the mask explicitly to avoid it being inherited across
+	 * a subsequent fork().
+	 */
+	if (!mask || !__sched_setaffinity(p, mask))
+		return;
+
+	raw_spin_lock_irqsave(&p->pi_lock, flags);
+	release_user_cpus_ptr(p);
+	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+}
+
 void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 {
 #ifdef CONFIG_SCHED_DEBUG
@@ -6822,7 +6970,7 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 	}
 #endif
 again:
-	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK);
+	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
 	if (retval)
 		goto out_free_new_mask;
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a189bec13729..29c35b51411b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1956,6 +1956,7 @@ extern struct task_struct *pick_next_task_idle(struct rq *rq);
 #define SCA_CHECK		0x01
 #define SCA_MIGRATE_DISABLE	0x02
 #define SCA_MIGRATE_ENABLE	0x04
+#define SCA_USER		0x08
 
 #ifdef CONFIG_SMP
 
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 08/16] sched: Allow task CPU affinity to be restricted on asymmetric systems

[Will Deacon]

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

Although userspace can carefully manage the affinity masks for such
tasks, one place where it is particularly problematic is execve()
because the CPU on which the execve() is occurring may be incompatible
with the new application image. In such a situation, it is desirable to
restrict the affinity mask of the task and ensure that the new image is
entered on a compatible CPU. From userspace's point of view, this looks
the same as if the incompatible CPUs have been hotplugged off in the
task's affinity mask. Similarly, if a subsequent execve() reverts to
a compatible image, then the old affinity is restored if it is still
valid.

In preparation for restricting the affinity mask for compat tasks on
arm64 systems without uniform support for 32-bit applications, introduce
{force,relax}_compatible_cpus_allowed_ptr(), which respectively restrict
and restore the affinity mask for a task based on the compatible CPUs.

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/sched.h |   2 +
 kernel/sched/core.c   | 180 ++++++++++++++++++++++++++++++++++++++----
 kernel/sched/sched.h  |   1 +
 3 files changed, 167 insertions(+), 16 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index db32d4f7e5b3..91a6cfeae242 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1691,6 +1691,8 @@ extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
 extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
 extern void release_user_cpus_ptr(struct task_struct *p);
+extern void force_compatible_cpus_allowed_ptr(struct task_struct *p);
+extern void relax_compatible_cpus_allowed_ptr(struct task_struct *p);
 #else
 static inline void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d151446d5987..d3d5e8b33961 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2354,27 +2354,22 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
 }
 
 /*
- * Change a given task's CPU affinity. Migrate the thread to a
- * proper CPU and schedule it away if the CPU it's executing on
- * is removed from the allowed bitmask.
- *
- * NOTE: the caller must have a valid reference to the task, the
- * task must not exit() & deallocate itself prematurely. The
- * call is not atomic; no spinlocks may be held.
+ * Called with both p->pi_lock and rq->lock held; drops both before returning.
  */
-static int __set_cpus_allowed_ptr(struct task_struct *p,
-				  const struct cpumask *new_mask,
-				  u32 flags)
+static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
+					 const struct cpumask *new_mask,
+					 u32 flags,
+					 struct rq *rq,
+					 struct rq_flags *rf)
+	__releases(rq->lock)
+	__releases(p->pi_lock)
 {
 	const struct cpumask *cpu_valid_mask = cpu_active_mask;
 	const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
 	unsigned int dest_cpu;
-	struct rq_flags rf;
-	struct rq *rq;
 	int ret = 0;
 	bool kthread = p->flags & PF_KTHREAD;
 
-	rq = task_rq_lock(p, &rf);
 	update_rq_clock(rq);
 
 	if (kthread || is_migration_disabled(p)) {
@@ -2430,20 +2425,173 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 
 	__do_set_cpus_allowed(p, new_mask, flags);
 
-	return affine_move_task(rq, p, &rf, dest_cpu, flags);
+	if (flags & SCA_USER)
+		release_user_cpus_ptr(p);
+
+	return affine_move_task(rq, p, rf, dest_cpu, flags);
 
 out:
-	task_rq_unlock(rq, p, &rf);
+	task_rq_unlock(rq, p, rf);
 
 	return ret;
 }
 
+/*
+ * Change a given task's CPU affinity. Migrate the thread to a
+ * proper CPU and schedule it away if the CPU it's executing on
+ * is removed from the allowed bitmask.
+ *
+ * NOTE: the caller must have a valid reference to the task, the
+ * task must not exit() & deallocate itself prematurely. The
+ * call is not atomic; no spinlocks may be held.
+ */
+static int __set_cpus_allowed_ptr(struct task_struct *p,
+				  const struct cpumask *new_mask, u32 flags)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+
+	rq = task_rq_lock(p, &rf);
+	return __set_cpus_allowed_ptr_locked(p, new_mask, flags, rq, &rf);
+}
+
 int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 {
 	return __set_cpus_allowed_ptr(p, new_mask, 0);
 }
 EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
 
+/*
+ * Change a given task's CPU affinity to the intersection of its current
+ * affinity mask and @subset_mask, writing the resulting mask to @new_mask
+ * and pointing @p->user_cpus_ptr to a copy of the old mask.
+ * If the resulting mask is empty, leave the affinity unchanged and return
+ * -EINVAL.
+ */
+static int restrict_cpus_allowed_ptr(struct task_struct *p,
+				     struct cpumask *new_mask,
+				     const struct cpumask *subset_mask)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+	int err;
+	struct cpumask *user_mask = NULL;
+
+	if (!p->user_cpus_ptr) {
+		user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
+
+		if (!user_mask)
+			return -ENOMEM;
+	}
+
+	rq = task_rq_lock(p, &rf);
+
+	/*
+	 * Forcefully restricting the affinity of a deadline task is
+	 * likely to cause problems, so fail and noisily override the
+	 * mask entirely.
+	 */
+	if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
+		err = -EPERM;
+		goto err_unlock;
+	}
+
+	if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
+		err = -EINVAL;
+		goto err_unlock;
+	}
+
+	/*
+	 * We're about to butcher the task affinity, so keep track of what
+	 * the user asked for in case we're able to restore it later on.
+	 */
+	if (user_mask) {
+		cpumask_copy(user_mask, p->cpus_ptr);
+		p->user_cpus_ptr = user_mask;
+	}
+
+	return __set_cpus_allowed_ptr_locked(p, new_mask, 0, rq, &rf);
+
+err_unlock:
+	task_rq_unlock(rq, p, &rf);
+	kfree(user_mask);
+	return err;
+}
+
+/*
+ * Restrict the CPU affinity of task @p so that it is a subset of
+ * task_cpu_possible_mask() and point @p->user_cpu_ptr to a copy of the
+ * old affinity mask. If the resulting mask is empty, we warn and walk
+ * up the cpuset hierarchy until we find a suitable mask.
+ */
+void force_compatible_cpus_allowed_ptr(struct task_struct *p)
+{
+	cpumask_var_t new_mask;
+	const struct cpumask *override_mask = task_cpu_possible_mask(p);
+
+	alloc_cpumask_var(&new_mask, GFP_KERNEL);
+
+	/*
+	 * __migrate_task() can fail silently in the face of concurrent
+	 * offlining of the chosen destination CPU, so take the hotplug
+	 * lock to ensure that the migration succeeds.
+	 */
+	cpus_read_lock();
+	if (!cpumask_available(new_mask))
+		goto out_set_mask;
+
+	if (!restrict_cpus_allowed_ptr(p, new_mask, override_mask))
+		goto out_free_mask;
+
+	/*
+	 * We failed to find a valid subset of the affinity mask for the
+	 * task, so override it based on its cpuset hierarchy.
+	 */
+	cpuset_cpus_allowed(p, new_mask);
+	override_mask = new_mask;
+
+out_set_mask:
+	if (printk_ratelimit()) {
+		printk_deferred("Overriding affinity for process %d (%s) to CPUs %*pbl\n",
+				task_pid_nr(p), p->comm,
+				cpumask_pr_args(override_mask));
+	}
+
+	WARN_ON(set_cpus_allowed_ptr(p, override_mask));
+out_free_mask:
+	cpus_read_unlock();
+	free_cpumask_var(new_mask);
+}
+
+static int
+__sched_setaffinity(struct task_struct *p, const struct cpumask *mask);
+
+/*
+ * Restore the affinity of a task @p which was previously restricted by a
+ * call to force_compatible_cpus_allowed_ptr(). This will clear (and free)
+ * @p->user_cpus_ptr.
+ *
+ * It is the caller's responsibility to serialise this with any calls to
+ * force_compatible_cpus_allowed_ptr(@p).
+ */
+void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
+{
+	unsigned long flags;
+	struct cpumask *mask = p->user_cpus_ptr;
+
+	/*
+	 * Try to restore the old affinity mask. If this fails, then
+	 * we free the mask explicitly to avoid it being inherited across
+	 * a subsequent fork().
+	 */
+	if (!mask || !__sched_setaffinity(p, mask))
+		return;
+
+	raw_spin_lock_irqsave(&p->pi_lock, flags);
+	release_user_cpus_ptr(p);
+	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+}
+
 void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 {
 #ifdef CONFIG_SCHED_DEBUG
@@ -6822,7 +6970,7 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 	}
 #endif
 again:
-	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK);
+	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
 	if (retval)
 		goto out_free_new_mask;
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a189bec13729..29c35b51411b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1956,6 +1956,7 @@ extern struct task_struct *pick_next_task_idle(struct rq *rq);
 #define SCA_CHECK		0x01
 #define SCA_MIGRATE_DISABLE	0x02
 #define SCA_MIGRATE_ENABLE	0x04
+#define SCA_USER		0x08
 
 #ifdef CONFIG_SMP
 
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 09/16] sched: Introduce dl_task_check_affinity() to check proposed affinity

[Will Deacon]

In preparation for restricting the affinity of a task during execve()
on arm64, introduce a new dl_task_check_affinity() helper function to
give an indication as to whether the restricted mask is admissible for
a deadline task.

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/sched.h |  6 ++++++
 kernel/sched/core.c   | 46 +++++++++++++++++++++++++++----------------
 2 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 91a6cfeae242..b9d0df8f7153 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1691,6 +1691,7 @@ extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
 extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
 extern void release_user_cpus_ptr(struct task_struct *p);
+extern int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask);
 extern void force_compatible_cpus_allowed_ptr(struct task_struct *p);
 extern void relax_compatible_cpus_allowed_ptr(struct task_struct *p);
 #else
@@ -1713,6 +1714,11 @@ static inline void release_user_cpus_ptr(struct task_struct *p)
 {
 	WARN_ON(p->user_cpus_ptr);
 }
+
+static inline int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
+{
+	return 0;
+}
 #endif
 
 extern int yield_to(struct task_struct *p, bool preempt);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d3d5e8b33961..d2fe6f8b8f6f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6935,6 +6935,32 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	return retval;
 }
 
+#ifdef CONFIG_SMP
+int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
+{
+	int ret = 0;
+
+	/*
+	 * If the task isn't a deadline task or admission control is
+	 * disabled then we don't care about affinity changes.
+	 */
+	if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
+		return 0;
+
+	/*
+	 * Since bandwidth control happens on root_domain basis,
+	 * if admission test is enabled, we only admit -deadline
+	 * tasks allowed to run on all the CPUs in the task's
+	 * root_domain.
+	 */
+	rcu_read_lock();
+	if (!cpumask_subset(task_rq(p)->rd->span, mask))
+		ret = -EBUSY;
+	rcu_read_unlock();
+	return ret;
+}
+#endif
+
 static int
 __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 {
@@ -6952,23 +6978,9 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 	cpuset_cpus_allowed(p, cpus_allowed);
 	cpumask_and(new_mask, mask, cpus_allowed);
 
-	/*
-	 * Since bandwidth control happens on root_domain basis,
-	 * if admission test is enabled, we only admit -deadline
-	 * tasks allowed to run on all the CPUs in the task's
-	 * root_domain.
-	 */
-#ifdef CONFIG_SMP
-	if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
-		rcu_read_lock();
-		if (!cpumask_subset(task_rq(p)->rd->span, new_mask)) {
-			retval = -EBUSY;
-			rcu_read_unlock();
-			goto out_free_new_mask;
-		}
-		rcu_read_unlock();
-	}
-#endif
+	retval = dl_task_check_affinity(p, new_mask);
+	if (retval)
+		goto out_free_new_mask;
 again:
 	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
 	if (retval)
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 09/16] sched: Introduce dl_task_check_affinity() to check proposed affinity

[Will Deacon]

In preparation for restricting the affinity of a task during execve()
on arm64, introduce a new dl_task_check_affinity() helper function to
give an indication as to whether the restricted mask is admissible for
a deadline task.

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/sched.h |  6 ++++++
 kernel/sched/core.c   | 46 +++++++++++++++++++++++++++----------------
 2 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 91a6cfeae242..b9d0df8f7153 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1691,6 +1691,7 @@ extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
 extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
 extern void release_user_cpus_ptr(struct task_struct *p);
+extern int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask);
 extern void force_compatible_cpus_allowed_ptr(struct task_struct *p);
 extern void relax_compatible_cpus_allowed_ptr(struct task_struct *p);
 #else
@@ -1713,6 +1714,11 @@ static inline void release_user_cpus_ptr(struct task_struct *p)
 {
 	WARN_ON(p->user_cpus_ptr);
 }
+
+static inline int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
+{
+	return 0;
+}
 #endif
 
 extern int yield_to(struct task_struct *p, bool preempt);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d3d5e8b33961..d2fe6f8b8f6f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6935,6 +6935,32 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	return retval;
 }
 
+#ifdef CONFIG_SMP
+int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
+{
+	int ret = 0;
+
+	/*
+	 * If the task isn't a deadline task or admission control is
+	 * disabled then we don't care about affinity changes.
+	 */
+	if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
+		return 0;
+
+	/*
+	 * Since bandwidth control happens on root_domain basis,
+	 * if admission test is enabled, we only admit -deadline
+	 * tasks allowed to run on all the CPUs in the task's
+	 * root_domain.
+	 */
+	rcu_read_lock();
+	if (!cpumask_subset(task_rq(p)->rd->span, mask))
+		ret = -EBUSY;
+	rcu_read_unlock();
+	return ret;
+}
+#endif
+
 static int
 __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 {
@@ -6952,23 +6978,9 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 	cpuset_cpus_allowed(p, cpus_allowed);
 	cpumask_and(new_mask, mask, cpus_allowed);
 
-	/*
-	 * Since bandwidth control happens on root_domain basis,
-	 * if admission test is enabled, we only admit -deadline
-	 * tasks allowed to run on all the CPUs in the task's
-	 * root_domain.
-	 */
-#ifdef CONFIG_SMP
-	if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
-		rcu_read_lock();
-		if (!cpumask_subset(task_rq(p)->rd->span, new_mask)) {
-			retval = -EBUSY;
-			rcu_read_unlock();
-			goto out_free_new_mask;
-		}
-		rcu_read_unlock();
-	}
-#endif
+	retval = dl_task_check_affinity(p, new_mask);
+	if (retval)
+		goto out_free_new_mask;
 again:
 	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
 	if (retval)
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 10/16] arm64: Implement task_cpu_possible_mask()

[Will Deacon]

Provide an implementation of task_cpu_possible_mask() so that we can
prevent 64-bit-only cores being added to the 'cpus_mask' for compat
tasks on systems with mismatched 32-bit support at EL0,

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/mmu_context.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index d3cef9133539..bb9b7510f334 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -231,6 +231,19 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	update_saved_ttbr0(tsk, next);
 }
 
+static inline const struct cpumask *
+task_cpu_possible_mask(struct task_struct *p)
+{
+	if (!static_branch_unlikely(&arm64_mismatched_32bit_el0))
+		return cpu_possible_mask;
+
+	if (!is_compat_thread(task_thread_info(p)))
+		return cpu_possible_mask;
+
+	return system_32bit_el0_cpumask();
+}
+#define task_cpu_possible_mask	task_cpu_possible_mask
+
 void verify_cpu_asid_bits(void);
 void post_ttbr_update_workaround(void);
 
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 10/16] arm64: Implement task_cpu_possible_mask()

[Will Deacon]

Provide an implementation of task_cpu_possible_mask() so that we can
prevent 64-bit-only cores being added to the 'cpus_mask' for compat
tasks on systems with mismatched 32-bit support at EL0,

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/mmu_context.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index d3cef9133539..bb9b7510f334 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -231,6 +231,19 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	update_saved_ttbr0(tsk, next);
 }
 
+static inline const struct cpumask *
+task_cpu_possible_mask(struct task_struct *p)
+{
+	if (!static_branch_unlikely(&arm64_mismatched_32bit_el0))
+		return cpu_possible_mask;
+
+	if (!is_compat_thread(task_thread_info(p)))
+		return cpu_possible_mask;
+
+	return system_32bit_el0_cpumask();
+}
+#define task_cpu_possible_mask	task_cpu_possible_mask
+
 void verify_cpu_asid_bits(void);
 void post_ttbr_update_workaround(void);
 
-- 
2.32.0.93.g670b81a890-goog


_______________________________________________
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 11/16] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0

[Will Deacon]

When exec'ing a 32-bit task on a system with mismatched support for
32-bit EL0, try to ensure that it starts life on a CPU that can actually
run it.

Similarly, when exec'ing a 64-bit task on such a system, try to restore
the old affinity mask if it was previously restricted.

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/elf.h |  6 ++----
 arch/arm64/kernel/process.c  | 39 +++++++++++++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 8d1c8dcb87fd..97932fbf973d 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -213,10 +213,8 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
 
 /* AArch32 EABI. */
 #define EF_ARM_EABI_MASK		0xff000000
-#define compat_elf_check_arch(x)	(system_supports_32bit_el0() && \
-					 ((x)->e_machine == EM_ARM) && \
-					 ((x)->e_flags & EF_ARM_EABI_MASK))
-
+int compat_elf_check_arch(const struct elf32_hdr *);
+#define compat_elf_check_arch		compat_elf_check_arch
 #define compat_start_thread		compat_start_thread
 /*
  * Unlike the native SET_PERSONALITY macro, the compat version maintains
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index f4a91bf1ce0c..220134888d7e 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -22,6 +22,7 @@
 #include <linux/mman.h>
 #include <linux/mm.h>
 #include <linux/nospec.h>
+#include <linux/sched.h>
 #include <linux/stddef.h>
 #include <linux/sysctl.h>
 #include <linux/unistd.h>
@@ -638,6 +639,28 @@ unsigned long arch_align_stack(unsigned long sp)
 	return sp & ~0xf;
 }
 
+#ifdef CONFIG_COMPAT
+int compat_elf_check_arch(const struct elf32_hdr *hdr)
+{
+	if (!system_supports_32bit_el0())
+		return false;
+
+	if ((hdr)->e_machine != EM_ARM)
+		return false;
+
+	if (!((hdr)->e_flags & EF_ARM_EABI_MASK))
+		return false;
+
+	/*
+	 * Prevent execve() of a 32-bit program from a deadline task
+	 * if the restricted affinity mask would be inadmissible on an
+	 * asymmetric system.
+	 */
+	return !static_branch_unlikely(&arm64_mismatched_32bit_el0) ||
+	       !dl_task_check_affinity(current, system_32bit_el0_cpumask());
+}
+#endif
+
 /*
  * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
  */
@@ -647,8 +670,22 @@ void arch_setup_new_exec(void)
 
 	if (is_compat_task()) {
 		mmflags = MMCF_AARCH32;
-		if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
+
+		/*
+		 * Restrict the CPU affinity mask for a 32-bit task so that
+		 * it contains only 32-bit-capable CPUs.
+		 *
+		 * From the perspective of the task, this looks similar to
+		 * what would happen if the 64-bit-only CPUs were hot-unplugged
+		 * at the point of execve(), although we try a bit harder to
+		 * honour the cpuset hierarchy.
+		 */
+		if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+			force_compatible_cpus_allowed_ptr(current);
 			set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+		}
+	} else if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+		relax_compatible_cpus_allowed_ptr(current);
 	}
 
 	current->mm->context.flags = mmflags;
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 11/16] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0

[Will Deacon]

When exec'ing a 32-bit task on a system with mismatched support for
32-bit EL0, try to ensure that it starts life on a CPU that can actually
run it.

Similarly, when exec'ing a 64-bit task on such a system, try to restore
the old affinity mask if it was previously restricted.

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/elf.h |  6 ++----
 arch/arm64/kernel/process.c  | 39 +++++++++++++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 8d1c8dcb87fd..97932fbf973d 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -213,10 +213,8 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
 
 /* AArch32 EABI. */
 #define EF_ARM_EABI_MASK		0xff000000
-#define compat_elf_check_arch(x)	(system_supports_32bit_el0() && \
-					 ((x)->e_machine == EM_ARM) && \
-					 ((x)->e_flags & EF_ARM_EABI_MASK))
-
+int compat_elf_check_arch(const struct elf32_hdr *);
+#define compat_elf_check_arch		compat_elf_check_arch
 #define compat_start_thread		compat_start_thread
 /*
  * Unlike the native SET_PERSONALITY macro, the compat version maintains
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index f4a91bf1ce0c..220134888d7e 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -22,6 +22,7 @@
 #include <linux/mman.h>
 #include <linux/mm.h>
 #include <linux/nospec.h>
+#include <linux/sched.h>
 #include <linux/stddef.h>
 #include <linux/sysctl.h>
 #include <linux/unistd.h>
@@ -638,6 +639,28 @@ unsigned long arch_align_stack(unsigned long sp)
 	return sp & ~0xf;
 }
 
+#ifdef CONFIG_COMPAT
+int compat_elf_check_arch(const struct elf32_hdr *hdr)
+{
+	if (!system_supports_32bit_el0())
+		return false;
+
+	if ((hdr)->e_machine != EM_ARM)
+		return false;
+
+	if (!((hdr)->e_flags & EF_ARM_EABI_MASK))
+		return false;
+
+	/*
+	 * Prevent execve() of a 32-bit program from a deadline task
+	 * if the restricted affinity mask would be inadmissible on an
+	 * asymmetric system.
+	 */
+	return !static_branch_unlikely(&arm64_mismatched_32bit_el0) ||
+	       !dl_task_check_affinity(current, system_32bit_el0_cpumask());
+}
+#endif
+
 /*
  * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
  */
@@ -647,8 +670,22 @@ void arch_setup_new_exec(void)
 
 	if (is_compat_task()) {
 		mmflags = MMCF_AARCH32;
-		if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
+
+		/*
+		 * Restrict the CPU affinity mask for a 32-bit task so that
+		 * it contains only 32-bit-capable CPUs.
+		 *
+		 * From the perspective of the task, this looks similar to
+		 * what would happen if the 64-bit-only CPUs were hot-unplugged
+		 * at the point of execve(), although we try a bit harder to
+		 * honour the cpuset hierarchy.
+		 */
+		if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+			force_compatible_cpus_allowed_ptr(current);
 			set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+		}
+	} else if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+		relax_compatible_cpus_allowed_ptr(current);
 	}
 
 	current->mm->context.flags = mmflags;
-- 
2.32.0.93.g670b81a890-goog


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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v10 12/16] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system

[Will Deacon]

If we want to support 32-bit applications, then when we identify a CPU
with mismatched 32-bit EL0 support we must ensure that we will always
have an active 32-bit CPU available to us from then on. This is important
for the scheduler, because is_cpu_allowed() will be constrained to 32-bit
CPUs for compat tasks and forced migration due to a hotplug event will
hang if no 32-bit CPUs are available.

On detecting a mismatch, prevent offlining of either the mismatching CPU
if it is 32-bit capable, or find the first active 32-bit capable CPU
otherwise.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index dbae006f625f..2f9fe57ead97 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2899,15 +2899,38 @@ void __init setup_cpu_features(void)
 
 static int enable_mismatched_32bit_el0(unsigned int cpu)
 {
+	/*
+	 * The first 32-bit-capable CPU we detected and so can no longer
+	 * be offlined by userspace. -1 indicates we haven't yet onlined
+	 * a 32-bit-capable CPU.
+	 */
+	static int lucky_winner = -1;
+
 	struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu);
 	bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0);
 
 	if (cpu_32bit) {
 		cpumask_set_cpu(cpu, cpu_32bit_el0_mask);
 		static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0);
-		setup_elf_hwcaps(compat_elf_hwcaps);
 	}
 
+	if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit)
+		return 0;
+
+	if (lucky_winner >= 0)
+		return 0;
+
+	/*
+	 * We've detected a mismatch. We need to keep one of our CPUs with
+	 * 32-bit EL0 online so that is_cpu_allowed() doesn't end up rejecting
+	 * every CPU in the system for a 32-bit task.
+	 */
+	lucky_winner = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask,
+							 cpu_active_mask);
+	get_cpu_device(lucky_winner)->offline_disabled = true;
+	setup_elf_hwcaps(compat_elf_hwcaps);
+	pr_info("Asymmetric 32-bit EL0 support detected on CPU %u; CPU hot-unplug disabled on CPU %u\n",
+		cpu, lucky_winner);
 	return 0;
 }
 
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 12/16] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system

[Will Deacon]

If we want to support 32-bit applications, then when we identify a CPU
with mismatched 32-bit EL0 support we must ensure that we will always
have an active 32-bit CPU available to us from then on. This is important
for the scheduler, because is_cpu_allowed() will be constrained to 32-bit
CPUs for compat tasks and forced migration due to a hotplug event will
hang if no 32-bit CPUs are available.

On detecting a mismatch, prevent offlining of either the mismatching CPU
if it is 32-bit capable, or find the first active 32-bit capable CPU
otherwise.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index dbae006f625f..2f9fe57ead97 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2899,15 +2899,38 @@ void __init setup_cpu_features(void)
 
 static int enable_mismatched_32bit_el0(unsigned int cpu)
 {
+	/*
+	 * The first 32-bit-capable CPU we detected and so can no longer
+	 * be offlined by userspace. -1 indicates we haven't yet onlined
+	 * a 32-bit-capable CPU.
+	 */
+	static int lucky_winner = -1;
+
 	struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu);
 	bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0);
 
 	if (cpu_32bit) {
 		cpumask_set_cpu(cpu, cpu_32bit_el0_mask);
 		static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0);
-		setup_elf_hwcaps(compat_elf_hwcaps);
 	}
 
+	if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit)
+		return 0;
+
+	if (lucky_winner >= 0)
+		return 0;
+
+	/*
+	 * We've detected a mismatch. We need to keep one of our CPUs with
+	 * 32-bit EL0 online so that is_cpu_allowed() doesn't end up rejecting
+	 * every CPU in the system for a 32-bit task.
+	 */
+	lucky_winner = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask,
+							 cpu_active_mask);
+	get_cpu_device(lucky_winner)->offline_disabled = true;
+	setup_elf_hwcaps(compat_elf_hwcaps);
+	pr_info("Asymmetric 32-bit EL0 support detected on CPU %u; CPU hot-unplug disabled on CPU %u\n",
+		cpu, lucky_winner);
 	return 0;
 }
 
-- 
2.32.0.93.g670b81a890-goog


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[PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Will Deacon]

Since 32-bit applications will be killed if they are caught trying to
execute on a 64-bit-only CPU in a mismatched system, advertise the set
of 32-bit capable CPUs to userspace in sysfs.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
 arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index fe13baa53c59..899377b2715a 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
 		'identification' directory exposes the CPU ID registers for
 		identifying model and revision of the CPU.
 
+What:		/sys/devices/system/cpu/aarch32_el0
+Date:		May 2021
+Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
+Description:	Identifies the subset of CPUs in the system that can execute
+		AArch32 (32-bit ARM) applications. If present, the same format as
+		/sys/devices/system/cpu/{offline,online,possible,present} is used.
+		If absent, then all or none of the CPUs can execute AArch32
+		applications and execve() will behave accordingly.
+
 What:		/sys/devices/system/cpu/cpu#/cpu_capacity
 Date:		December 2016
 Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 2f9fe57ead97..23eaa7f06f76 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -67,6 +67,7 @@
 #include <linux/crash_dump.h>
 #include <linux/sort.h>
 #include <linux/stop_machine.h>
+#include <linux/sysfs.h>
 #include <linux/types.h>
 #include <linux/minmax.h>
 #include <linux/mm.h>
@@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
 	return cpu_possible_mask;
 }
 
+static ssize_t aarch32_el0_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	const struct cpumask *mask = system_32bit_el0_cpumask();
+
+	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
+}
+static const DEVICE_ATTR_RO(aarch32_el0);
+
+static int __init aarch32_el0_sysfs_init(void)
+{
+	if (!allow_mismatched_32bit_el0)
+		return 0;
+
+	return device_create_file(cpu_subsys.dev_root, &dev_attr_aarch32_el0);
+}
+device_initcall(aarch32_el0_sysfs_init);
+
 static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope)
 {
 	if (!has_cpuid_feature(entry, scope))
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Will Deacon]

Since 32-bit applications will be killed if they are caught trying to
execute on a 64-bit-only CPU in a mismatched system, advertise the set
of 32-bit capable CPUs to userspace in sysfs.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
 arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index fe13baa53c59..899377b2715a 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
 		'identification' directory exposes the CPU ID registers for
 		identifying model and revision of the CPU.
 
+What:		/sys/devices/system/cpu/aarch32_el0
+Date:		May 2021
+Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
+Description:	Identifies the subset of CPUs in the system that can execute
+		AArch32 (32-bit ARM) applications. If present, the same format as
+		/sys/devices/system/cpu/{offline,online,possible,present} is used.
+		If absent, then all or none of the CPUs can execute AArch32
+		applications and execve() will behave accordingly.
+
 What:		/sys/devices/system/cpu/cpu#/cpu_capacity
 Date:		December 2016
 Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 2f9fe57ead97..23eaa7f06f76 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -67,6 +67,7 @@
 #include <linux/crash_dump.h>
 #include <linux/sort.h>
 #include <linux/stop_machine.h>
+#include <linux/sysfs.h>
 #include <linux/types.h>
 #include <linux/minmax.h>
 #include <linux/mm.h>
@@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
 	return cpu_possible_mask;
 }
 
+static ssize_t aarch32_el0_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	const struct cpumask *mask = system_32bit_el0_cpumask();
+
+	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
+}
+static const DEVICE_ATTR_RO(aarch32_el0);
+
+static int __init aarch32_el0_sysfs_init(void)
+{
+	if (!allow_mismatched_32bit_el0)
+		return 0;
+
+	return device_create_file(cpu_subsys.dev_root, &dev_attr_aarch32_el0);
+}
+device_initcall(aarch32_el0_sysfs_init);
+
 static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope)
 {
 	if (!has_cpuid_feature(entry, scope))
-- 
2.32.0.93.g670b81a890-goog


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Re: [PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Greg Kroah-Hartman]

On Wed, Jun 23, 2021 at 06:38:45PM +0100, Will Deacon wrote:
> Since 32-bit applications will be killed if they are caught trying to
> execute on a 64-bit-only CPU in a mismatched system, advertise the set
> of 32-bit capable CPUs to userspace in sysfs.
> 
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
>  arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index fe13baa53c59..899377b2715a 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
>  		'identification' directory exposes the CPU ID registers for
>  		identifying model and revision of the CPU.
>  
> +What:		/sys/devices/system/cpu/aarch32_el0
> +Date:		May 2021
> +Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
> +Description:	Identifies the subset of CPUs in the system that can execute
> +		AArch32 (32-bit ARM) applications. If present, the same format as
> +		/sys/devices/system/cpu/{offline,online,possible,present} is used.
> +		If absent, then all or none of the CPUs can execute AArch32
> +		applications and execve() will behave accordingly.
> +
>  What:		/sys/devices/system/cpu/cpu#/cpu_capacity
>  Date:		December 2016
>  Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 2f9fe57ead97..23eaa7f06f76 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -67,6 +67,7 @@
>  #include <linux/crash_dump.h>
>  #include <linux/sort.h>
>  #include <linux/stop_machine.h>
> +#include <linux/sysfs.h>
>  #include <linux/types.h>
>  #include <linux/minmax.h>
>  #include <linux/mm.h>
> @@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
>  	return cpu_possible_mask;
>  }
>  
> +static ssize_t aarch32_el0_show(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	const struct cpumask *mask = system_32bit_el0_cpumask();
> +
> +	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
> +}
> +static const DEVICE_ATTR_RO(aarch32_el0);

I just realized that we have a problem with this type of representation
overflowing PAGE_SIZE on larger systems.  There is ongoing work to fix
this up but that requires converting these to binary sysfs files, which
is a pain to preserve the original format here.

Yes, for now you will be fine on these arm32 systems, but in the future
this will have to be changed.  Because of that, should you just make
this an individual cpu attribute (one file per cpu) and not a single
file that lists all cpus?

what tool is going to read this and why can't they just pick it up from
the individual cpu files instead?

thanks,

greg k-h

Re: [PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Greg Kroah-Hartman]

On Wed, Jun 23, 2021 at 06:38:45PM +0100, Will Deacon wrote:
> Since 32-bit applications will be killed if they are caught trying to
> execute on a 64-bit-only CPU in a mismatched system, advertise the set
> of 32-bit capable CPUs to userspace in sysfs.
> 
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
>  arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index fe13baa53c59..899377b2715a 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
>  		'identification' directory exposes the CPU ID registers for
>  		identifying model and revision of the CPU.
>  
> +What:		/sys/devices/system/cpu/aarch32_el0
> +Date:		May 2021
> +Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
> +Description:	Identifies the subset of CPUs in the system that can execute
> +		AArch32 (32-bit ARM) applications. If present, the same format as
> +		/sys/devices/system/cpu/{offline,online,possible,present} is used.
> +		If absent, then all or none of the CPUs can execute AArch32
> +		applications and execve() will behave accordingly.
> +
>  What:		/sys/devices/system/cpu/cpu#/cpu_capacity
>  Date:		December 2016
>  Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 2f9fe57ead97..23eaa7f06f76 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -67,6 +67,7 @@
>  #include <linux/crash_dump.h>
>  #include <linux/sort.h>
>  #include <linux/stop_machine.h>
> +#include <linux/sysfs.h>
>  #include <linux/types.h>
>  #include <linux/minmax.h>
>  #include <linux/mm.h>
> @@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
>  	return cpu_possible_mask;
>  }
>  
> +static ssize_t aarch32_el0_show(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	const struct cpumask *mask = system_32bit_el0_cpumask();
> +
> +	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
> +}
> +static const DEVICE_ATTR_RO(aarch32_el0);

I just realized that we have a problem with this type of representation
overflowing PAGE_SIZE on larger systems.  There is ongoing work to fix
this up but that requires converting these to binary sysfs files, which
is a pain to preserve the original format here.

Yes, for now you will be fine on these arm32 systems, but in the future
this will have to be changed.  Because of that, should you just make
this an individual cpu attribute (one file per cpu) and not a single
file that lists all cpus?

what tool is going to read this and why can't they just pick it up from
the individual cpu files instead?

thanks,

greg k-h

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Will Deacon]

Hi Greg,

On Fri, Jun 25, 2021 at 10:46:35AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Jun 23, 2021 at 06:38:45PM +0100, Will Deacon wrote:
> > Since 32-bit applications will be killed if they are caught trying to
> > execute on a 64-bit-only CPU in a mismatched system, advertise the set
> > of 32-bit capable CPUs to userspace in sysfs.
> > 
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > Signed-off-by: Will Deacon <will@kernel.org>
> > ---
> >  .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
> >  arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
> >  2 files changed, 28 insertions(+)
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > index fe13baa53c59..899377b2715a 100644
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
> >  		'identification' directory exposes the CPU ID registers for
> >  		identifying model and revision of the CPU.
> >  
> > +What:		/sys/devices/system/cpu/aarch32_el0
> > +Date:		May 2021
> > +Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
> > +Description:	Identifies the subset of CPUs in the system that can execute
> > +		AArch32 (32-bit ARM) applications. If present, the same format as
> > +		/sys/devices/system/cpu/{offline,online,possible,present} is used.
> > +		If absent, then all or none of the CPUs can execute AArch32
> > +		applications and execve() will behave accordingly.
> > +
> >  What:		/sys/devices/system/cpu/cpu#/cpu_capacity
> >  Date:		December 2016
> >  Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 2f9fe57ead97..23eaa7f06f76 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -67,6 +67,7 @@
> >  #include <linux/crash_dump.h>
> >  #include <linux/sort.h>
> >  #include <linux/stop_machine.h>
> > +#include <linux/sysfs.h>
> >  #include <linux/types.h>
> >  #include <linux/minmax.h>
> >  #include <linux/mm.h>
> > @@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
> >  	return cpu_possible_mask;
> >  }
> >  
> > +static ssize_t aarch32_el0_show(struct device *dev,
> > +				struct device_attribute *attr, char *buf)
> > +{
> > +	const struct cpumask *mask = system_32bit_el0_cpumask();
> > +
> > +	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
> > +}
> > +static const DEVICE_ATTR_RO(aarch32_el0);
> 
> I just realized that we have a problem with this type of representation
> overflowing PAGE_SIZE on larger systems.  There is ongoing work to fix
> this up but that requires converting these to binary sysfs files, which
> is a pain to preserve the original format here.

Urgh. Do you have a link to the work trying to fix this for the other sysfs
files which are affected by this problem, please?

> Yes, for now you will be fine on these arm32 systems, but in the future
> this will have to be changed.  Because of that, should you just make
> this an individual cpu attribute (one file per cpu) and not a single
> file that lists all cpus?

Practically, I don't see this will ever be an issue for this case:

  1. 32-bit support is going to go away from the hardware, so this file
     will simply be empty in the future.

  2. The 32-bit-capable CPUs aren't dotted around randomly, but rather
     exist as contiguous ranges, so the format is reasonably compact.

> what tool is going to read this and why can't they just pick it up from
> the individual cpu files instead?

The idea is that controlling the affinity of 32-bit applications explicitly
in userspace can be done by either creating cpusets where all CPUs are
32-bit capable, or simply setting their affinity to include only
32-bit-capable CPUs. The really nice properties about the way this is
currently exposed are that it is the same as the
/sys/devices/system/cpu/{offline,online,possible,present} files and is
readibly usable by scripts. Moving the information into a per-cpu file gets
rid of both of those advantages :(

A middle ground would be to expose it as a mask (i.e. "%*pb") and use one
bit per CPU. NR_CPUS is capped to 4k on arm64 so that would be sufficient,
although then the format is weirdly different to the other masks in the same
directory.

Will

Re: [PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Will Deacon]

Hi Greg,

On Fri, Jun 25, 2021 at 10:46:35AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Jun 23, 2021 at 06:38:45PM +0100, Will Deacon wrote:
> > Since 32-bit applications will be killed if they are caught trying to
> > execute on a 64-bit-only CPU in a mismatched system, advertise the set
> > of 32-bit capable CPUs to userspace in sysfs.
> > 
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > Signed-off-by: Will Deacon <will@kernel.org>
> > ---
> >  .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
> >  arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
> >  2 files changed, 28 insertions(+)
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > index fe13baa53c59..899377b2715a 100644
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
> >  		'identification' directory exposes the CPU ID registers for
> >  		identifying model and revision of the CPU.
> >  
> > +What:		/sys/devices/system/cpu/aarch32_el0
> > +Date:		May 2021
> > +Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
> > +Description:	Identifies the subset of CPUs in the system that can execute
> > +		AArch32 (32-bit ARM) applications. If present, the same format as
> > +		/sys/devices/system/cpu/{offline,online,possible,present} is used.
> > +		If absent, then all or none of the CPUs can execute AArch32
> > +		applications and execve() will behave accordingly.
> > +
> >  What:		/sys/devices/system/cpu/cpu#/cpu_capacity
> >  Date:		December 2016
> >  Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 2f9fe57ead97..23eaa7f06f76 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -67,6 +67,7 @@
> >  #include <linux/crash_dump.h>
> >  #include <linux/sort.h>
> >  #include <linux/stop_machine.h>
> > +#include <linux/sysfs.h>
> >  #include <linux/types.h>
> >  #include <linux/minmax.h>
> >  #include <linux/mm.h>
> > @@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
> >  	return cpu_possible_mask;
> >  }
> >  
> > +static ssize_t aarch32_el0_show(struct device *dev,
> > +				struct device_attribute *attr, char *buf)
> > +{
> > +	const struct cpumask *mask = system_32bit_el0_cpumask();
> > +
> > +	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
> > +}
> > +static const DEVICE_ATTR_RO(aarch32_el0);
> 
> I just realized that we have a problem with this type of representation
> overflowing PAGE_SIZE on larger systems.  There is ongoing work to fix
> this up but that requires converting these to binary sysfs files, which
> is a pain to preserve the original format here.

Urgh. Do you have a link to the work trying to fix this for the other sysfs
files which are affected by this problem, please?

> Yes, for now you will be fine on these arm32 systems, but in the future
> this will have to be changed.  Because of that, should you just make
> this an individual cpu attribute (one file per cpu) and not a single
> file that lists all cpus?

Practically, I don't see this will ever be an issue for this case:

  1. 32-bit support is going to go away from the hardware, so this file
     will simply be empty in the future.

  2. The 32-bit-capable CPUs aren't dotted around randomly, but rather
     exist as contiguous ranges, so the format is reasonably compact.

> what tool is going to read this and why can't they just pick it up from
> the individual cpu files instead?

The idea is that controlling the affinity of 32-bit applications explicitly
in userspace can be done by either creating cpusets where all CPUs are
32-bit capable, or simply setting their affinity to include only
32-bit-capable CPUs. The really nice properties about the way this is
currently exposed are that it is the same as the
/sys/devices/system/cpu/{offline,online,possible,present} files and is
readibly usable by scripts. Moving the information into a per-cpu file gets
rid of both of those advantages :(

A middle ground would be to expose it as a mask (i.e. "%*pb") and use one
bit per CPU. NR_CPUS is capped to 4k on arm64 so that would be sufficient,
although then the format is weirdly different to the other masks in the same
directory.

Will

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Greg Kroah-Hartman]

On Fri, Jun 25, 2021 at 10:36:49AM +0100, Will Deacon wrote:
> Hi Greg,
> 
> On Fri, Jun 25, 2021 at 10:46:35AM +0200, Greg Kroah-Hartman wrote:
> > On Wed, Jun 23, 2021 at 06:38:45PM +0100, Will Deacon wrote:
> > > Since 32-bit applications will be killed if they are caught trying to
> > > execute on a 64-bit-only CPU in a mismatched system, advertise the set
> > > of 32-bit capable CPUs to userspace in sysfs.
> > > 
> > > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Signed-off-by: Will Deacon <will@kernel.org>
> > > ---
> > >  .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
> > >  arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
> > >  2 files changed, 28 insertions(+)
> > > 
> > > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > > index fe13baa53c59..899377b2715a 100644
> > > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > > @@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
> > >  		'identification' directory exposes the CPU ID registers for
> > >  		identifying model and revision of the CPU.
> > >  
> > > +What:		/sys/devices/system/cpu/aarch32_el0
> > > +Date:		May 2021
> > > +Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
> > > +Description:	Identifies the subset of CPUs in the system that can execute
> > > +		AArch32 (32-bit ARM) applications. If present, the same format as
> > > +		/sys/devices/system/cpu/{offline,online,possible,present} is used.
> > > +		If absent, then all or none of the CPUs can execute AArch32
> > > +		applications and execve() will behave accordingly.
> > > +
> > >  What:		/sys/devices/system/cpu/cpu#/cpu_capacity
> > >  Date:		December 2016
> > >  Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > > index 2f9fe57ead97..23eaa7f06f76 100644
> > > --- a/arch/arm64/kernel/cpufeature.c
> > > +++ b/arch/arm64/kernel/cpufeature.c
> > > @@ -67,6 +67,7 @@
> > >  #include <linux/crash_dump.h>
> > >  #include <linux/sort.h>
> > >  #include <linux/stop_machine.h>
> > > +#include <linux/sysfs.h>
> > >  #include <linux/types.h>
> > >  #include <linux/minmax.h>
> > >  #include <linux/mm.h>
> > > @@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
> > >  	return cpu_possible_mask;
> > >  }
> > >  
> > > +static ssize_t aarch32_el0_show(struct device *dev,
> > > +				struct device_attribute *attr, char *buf)
> > > +{
> > > +	const struct cpumask *mask = system_32bit_el0_cpumask();
> > > +
> > > +	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
> > > +}
> > > +static const DEVICE_ATTR_RO(aarch32_el0);
> > 
> > I just realized that we have a problem with this type of representation
> > overflowing PAGE_SIZE on larger systems.  There is ongoing work to fix
> > this up but that requires converting these to binary sysfs files, which
> > is a pain to preserve the original format here.
> 
> Urgh. Do you have a link to the work trying to fix this for the other sysfs
> files which are affected by this problem, please?

https://lore.kernel.org/r/20210617101910.13228-1-song.bao.hua@hisilicon.com
has the details.

> 
> > Yes, for now you will be fine on these arm32 systems, but in the future
> > this will have to be changed.  Because of that, should you just make
> > this an individual cpu attribute (one file per cpu) and not a single
> > file that lists all cpus?
> 
> Practically, I don't see this will ever be an issue for this case:
> 
>   1. 32-bit support is going to go away from the hardware, so this file
>      will simply be empty in the future.

It should not be "empty", it should just not be present if there are no
cpus of this type.

>   2. The 32-bit-capable CPUs aren't dotted around randomly, but rather
>      exist as contiguous ranges, so the format is reasonably compact.

We can dream :)

But again, why not just put a single file in the individual sysfs
directories for the cpus that are affected?  What is saved by providing
a range here?

> > what tool is going to read this and why can't they just pick it up from
> > the individual cpu files instead?
> 
> The idea is that controlling the affinity of 32-bit applications explicitly
> in userspace can be done by either creating cpusets where all CPUs are
> 32-bit capable, or simply setting their affinity to include only
> 32-bit-capable CPUs. The really nice properties about the way this is
> currently exposed are that it is the same as the
> /sys/devices/system/cpu/{offline,online,possible,present} files and is
> readibly usable by scripts. Moving the information into a per-cpu file gets
> rid of both of those advantages :(
> 
> A middle ground would be to expose it as a mask (i.e. "%*pb") and use one
> bit per CPU. NR_CPUS is capped to 4k on arm64 so that would be sufficient,
> although then the format is weirdly different to the other masks in the same
> directory.

See the link above for the details.  I would like to prevent the
addition of files that we know are already starting to cause problems in
real systems if at all possible.  If there really is no other way, ok,
but be aware of the future problems here please.

Yes, the odds of a lot of 32bit cpus in a single system are low, but
hardware engineers have done crazier things in the past...

thanks,

greg k-h

Re: [PATCH v10 13/16] arm64: Advertise CPUs capable of running 32-bit applications in sysfs

[Greg Kroah-Hartman]

On Fri, Jun 25, 2021 at 10:36:49AM +0100, Will Deacon wrote:
> Hi Greg,
> 
> On Fri, Jun 25, 2021 at 10:46:35AM +0200, Greg Kroah-Hartman wrote:
> > On Wed, Jun 23, 2021 at 06:38:45PM +0100, Will Deacon wrote:
> > > Since 32-bit applications will be killed if they are caught trying to
> > > execute on a 64-bit-only CPU in a mismatched system, advertise the set
> > > of 32-bit capable CPUs to userspace in sysfs.
> > > 
> > > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Signed-off-by: Will Deacon <will@kernel.org>
> > > ---
> > >  .../ABI/testing/sysfs-devices-system-cpu      |  9 +++++++++
> > >  arch/arm64/kernel/cpufeature.c                | 19 +++++++++++++++++++
> > >  2 files changed, 28 insertions(+)
> > > 
> > > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > > index fe13baa53c59..899377b2715a 100644
> > > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > > @@ -494,6 +494,15 @@ Description:	AArch64 CPU registers
> > >  		'identification' directory exposes the CPU ID registers for
> > >  		identifying model and revision of the CPU.
> > >  
> > > +What:		/sys/devices/system/cpu/aarch32_el0
> > > +Date:		May 2021
> > > +Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
> > > +Description:	Identifies the subset of CPUs in the system that can execute
> > > +		AArch32 (32-bit ARM) applications. If present, the same format as
> > > +		/sys/devices/system/cpu/{offline,online,possible,present} is used.
> > > +		If absent, then all or none of the CPUs can execute AArch32
> > > +		applications and execve() will behave accordingly.
> > > +
> > >  What:		/sys/devices/system/cpu/cpu#/cpu_capacity
> > >  Date:		December 2016
> > >  Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > > index 2f9fe57ead97..23eaa7f06f76 100644
> > > --- a/arch/arm64/kernel/cpufeature.c
> > > +++ b/arch/arm64/kernel/cpufeature.c
> > > @@ -67,6 +67,7 @@
> > >  #include <linux/crash_dump.h>
> > >  #include <linux/sort.h>
> > >  #include <linux/stop_machine.h>
> > > +#include <linux/sysfs.h>
> > >  #include <linux/types.h>
> > >  #include <linux/minmax.h>
> > >  #include <linux/mm.h>
> > > @@ -1319,6 +1320,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
> > >  	return cpu_possible_mask;
> > >  }
> > >  
> > > +static ssize_t aarch32_el0_show(struct device *dev,
> > > +				struct device_attribute *attr, char *buf)
> > > +{
> > > +	const struct cpumask *mask = system_32bit_el0_cpumask();
> > > +
> > > +	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
> > > +}
> > > +static const DEVICE_ATTR_RO(aarch32_el0);
> > 
> > I just realized that we have a problem with this type of representation
> > overflowing PAGE_SIZE on larger systems.  There is ongoing work to fix
> > this up but that requires converting these to binary sysfs files, which
> > is a pain to preserve the original format here.
> 
> Urgh. Do you have a link to the work trying to fix this for the other sysfs
> files which are affected by this problem, please?

https://lore.kernel.org/r/20210617101910.13228-1-song.bao.hua@hisilicon.com
has the details.

> 
> > Yes, for now you will be fine on these arm32 systems, but in the future
> > this will have to be changed.  Because of that, should you just make
> > this an individual cpu attribute (one file per cpu) and not a single
> > file that lists all cpus?
> 
> Practically, I don't see this will ever be an issue for this case:
> 
>   1. 32-bit support is going to go away from the hardware, so this file
>      will simply be empty in the future.

It should not be "empty", it should just not be present if there are no
cpus of this type.

>   2. The 32-bit-capable CPUs aren't dotted around randomly, but rather
>      exist as contiguous ranges, so the format is reasonably compact.

We can dream :)

But again, why not just put a single file in the individual sysfs
directories for the cpus that are affected?  What is saved by providing
a range here?

> > what tool is going to read this and why can't they just pick it up from
> > the individual cpu files instead?
> 
> The idea is that controlling the affinity of 32-bit applications explicitly
> in userspace can be done by either creating cpusets where all CPUs are
> 32-bit capable, or simply setting their affinity to include only
> 32-bit-capable CPUs. The really nice properties about the way this is
> currently exposed are that it is the same as the
> /sys/devices/system/cpu/{offline,online,possible,present} files and is
> readibly usable by scripts. Moving the information into a per-cpu file gets
> rid of both of those advantages :(
> 
> A middle ground would be to expose it as a mask (i.e. "%*pb") and use one
> bit per CPU. NR_CPUS is capped to 4k on arm64 so that would be sufficient,
> although then the format is weirdly different to the other masks in the same
> directory.

See the link above for the details.  I would like to prevent the
addition of files that we know are already starting to cause problems in
real systems if at all possible.  If there really is no other way, ok,
but be aware of the future problems here please.

Yes, the odds of a lot of 32bit cpus in a single system are low, but
hardware engineers have done crazier things in the past...

thanks,

greg k-h

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[PATCH v10 14/16] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0

[Will Deacon]

Allow systems with mismatched 32-bit support at EL0 to run 32-bit
applications based on a new kernel parameter.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++
 arch/arm64/kernel/cpufeature.c                  | 7 +++++++
 2 files changed, 15 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..a2e453919bb6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -287,6 +287,14 @@
 			do not want to use tracing_snapshot_alloc() as it needs
 			to be done where GFP_KERNEL allocations are allowed.
 
+	allow_mismatched_32bit_el0 [ARM64]
+			Allow execve() of 32-bit applications and setting of the
+			PER_LINUX32 personality on systems where only a strict
+			subset of the CPUs support 32-bit EL0. When this
+			parameter is present, the set of CPUs supporting 32-bit
+			EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
+			and hot-unplug operations may be restricted.
+
 	amd_iommu=	[HW,X86-64]
 			Pass parameters to the AMD IOMMU driver in the system.
 			Possible values are:
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 23eaa7f06f76..8c9f9a57626a 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1320,6 +1320,13 @@ const struct cpumask *system_32bit_el0_cpumask(void)
 	return cpu_possible_mask;
 }
 
+static int __init parse_32bit_el0_param(char *str)
+{
+	allow_mismatched_32bit_el0 = true;
+	return 0;
+}
+early_param("allow_mismatched_32bit_el0", parse_32bit_el0_param);
+
 static ssize_t aarch32_el0_show(struct device *dev,
 				struct device_attribute *attr, char *buf)
 {
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 14/16] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0

[Will Deacon]

Allow systems with mismatched 32-bit support at EL0 to run 32-bit
applications based on a new kernel parameter.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++
 arch/arm64/kernel/cpufeature.c                  | 7 +++++++
 2 files changed, 15 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..a2e453919bb6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -287,6 +287,14 @@
 			do not want to use tracing_snapshot_alloc() as it needs
 			to be done where GFP_KERNEL allocations are allowed.
 
+	allow_mismatched_32bit_el0 [ARM64]
+			Allow execve() of 32-bit applications and setting of the
+			PER_LINUX32 personality on systems where only a strict
+			subset of the CPUs support 32-bit EL0. When this
+			parameter is present, the set of CPUs supporting 32-bit
+			EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
+			and hot-unplug operations may be restricted.
+
 	amd_iommu=	[HW,X86-64]
 			Pass parameters to the AMD IOMMU driver in the system.
 			Possible values are:
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 23eaa7f06f76..8c9f9a57626a 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1320,6 +1320,13 @@ const struct cpumask *system_32bit_el0_cpumask(void)
 	return cpu_possible_mask;
 }
 
+static int __init parse_32bit_el0_param(char *str)
+{
+	allow_mismatched_32bit_el0 = true;
+	return 0;
+}
+early_param("allow_mismatched_32bit_el0", parse_32bit_el0_param);
+
 static ssize_t aarch32_el0_show(struct device *dev,
 				struct device_attribute *attr, char *buf)
 {
-- 
2.32.0.93.g670b81a890-goog


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[PATCH v10 15/16] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores

[Will Deacon]

The scheduler now knows enough about these braindead systems to place
32-bit tasks accordingly, so throw out the safety checks and allow the
ret-to-user path to avoid do_notify_resume() if there is nothing to do.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/process.c | 14 +-------------
 arch/arm64/kernel/signal.c  | 26 --------------------------
 2 files changed, 1 insertion(+), 39 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 220134888d7e..1de4d934db7f 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -528,15 +528,6 @@ static void erratum_1418040_thread_switch(struct task_struct *prev,
 	write_sysreg(val, cntkctl_el1);
 }
 
-static void compat_thread_switch(struct task_struct *next)
-{
-	if (!is_compat_thread(task_thread_info(next)))
-		return;
-
-	if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
-		set_tsk_thread_flag(next, TIF_NOTIFY_RESUME);
-}
-
 static void update_sctlr_el1(u64 sctlr)
 {
 	/*
@@ -578,7 +569,6 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	ssbs_thread_switch(next);
 	erratum_1418040_thread_switch(prev, next);
 	ptrauth_thread_switch_user(next);
-	compat_thread_switch(next);
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case
@@ -680,10 +670,8 @@ void arch_setup_new_exec(void)
 		 * at the point of execve(), although we try a bit harder to
 		 * honour the cpuset hierarchy.
 		 */
-		if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+		if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
 			force_compatible_cpus_allowed_ptr(current);
-			set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
-		}
 	} else if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
 		relax_compatible_cpus_allowed_ptr(current);
 	}
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index f8192f4ae0b8..6237486ff6bb 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -911,19 +911,6 @@ static void do_signal(struct pt_regs *regs)
 	restore_saved_sigmask();
 }
 
-static bool cpu_affinity_invalid(struct pt_regs *regs)
-{
-	if (!compat_user_mode(regs))
-		return false;
-
-	/*
-	 * We're preemptible, but a reschedule will cause us to check the
-	 * affinity again.
-	 */
-	return !cpumask_test_cpu(raw_smp_processor_id(),
-				 system_32bit_el0_cpumask());
-}
-
 asmlinkage void do_notify_resume(struct pt_regs *regs,
 				 unsigned long thread_flags)
 {
@@ -951,19 +938,6 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 			if (thread_flags & _TIF_NOTIFY_RESUME) {
 				tracehook_notify_resume(regs);
 				rseq_handle_notify_resume(NULL, regs);
-
-				/*
-				 * If we reschedule after checking the affinity
-				 * then we must ensure that TIF_NOTIFY_RESUME
-				 * is set so that we check the affinity again.
-				 * Since tracehook_notify_resume() clears the
-				 * flag, ensure that the compiler doesn't move
-				 * it after the affinity check.
-				 */
-				barrier();
-
-				if (cpu_affinity_invalid(regs))
-					force_sig(SIGKILL);
 			}
 
 			if (thread_flags & _TIF_FOREIGN_FPSTATE)
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 15/16] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores

[Will Deacon]

The scheduler now knows enough about these braindead systems to place
32-bit tasks accordingly, so throw out the safety checks and allow the
ret-to-user path to avoid do_notify_resume() if there is nothing to do.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/process.c | 14 +-------------
 arch/arm64/kernel/signal.c  | 26 --------------------------
 2 files changed, 1 insertion(+), 39 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 220134888d7e..1de4d934db7f 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -528,15 +528,6 @@ static void erratum_1418040_thread_switch(struct task_struct *prev,
 	write_sysreg(val, cntkctl_el1);
 }
 
-static void compat_thread_switch(struct task_struct *next)
-{
-	if (!is_compat_thread(task_thread_info(next)))
-		return;
-
-	if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
-		set_tsk_thread_flag(next, TIF_NOTIFY_RESUME);
-}
-
 static void update_sctlr_el1(u64 sctlr)
 {
 	/*
@@ -578,7 +569,6 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	ssbs_thread_switch(next);
 	erratum_1418040_thread_switch(prev, next);
 	ptrauth_thread_switch_user(next);
-	compat_thread_switch(next);
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case
@@ -680,10 +670,8 @@ void arch_setup_new_exec(void)
 		 * at the point of execve(), although we try a bit harder to
 		 * honour the cpuset hierarchy.
 		 */
-		if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+		if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
 			force_compatible_cpus_allowed_ptr(current);
-			set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
-		}
 	} else if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
 		relax_compatible_cpus_allowed_ptr(current);
 	}
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index f8192f4ae0b8..6237486ff6bb 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -911,19 +911,6 @@ static void do_signal(struct pt_regs *regs)
 	restore_saved_sigmask();
 }
 
-static bool cpu_affinity_invalid(struct pt_regs *regs)
-{
-	if (!compat_user_mode(regs))
-		return false;
-
-	/*
-	 * We're preemptible, but a reschedule will cause us to check the
-	 * affinity again.
-	 */
-	return !cpumask_test_cpu(raw_smp_processor_id(),
-				 system_32bit_el0_cpumask());
-}
-
 asmlinkage void do_notify_resume(struct pt_regs *regs,
 				 unsigned long thread_flags)
 {
@@ -951,19 +938,6 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 			if (thread_flags & _TIF_NOTIFY_RESUME) {
 				tracehook_notify_resume(regs);
 				rseq_handle_notify_resume(NULL, regs);
-
-				/*
-				 * If we reschedule after checking the affinity
-				 * then we must ensure that TIF_NOTIFY_RESUME
-				 * is set so that we check the affinity again.
-				 * Since tracehook_notify_resume() clears the
-				 * flag, ensure that the compiler doesn't move
-				 * it after the affinity check.
-				 */
-				barrier();
-
-				if (cpu_affinity_invalid(regs))
-					force_sig(SIGKILL);
 			}
 
 			if (thread_flags & _TIF_FOREIGN_FPSTATE)
-- 
2.32.0.93.g670b81a890-goog


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[PATCH v10 16/16] Documentation: arm64: describe asymmetric 32-bit support

[Will Deacon]

Document support for running 32-bit tasks on asymmetric 32-bit systems
and its impact on the user ABI when enabled.

Signed-off-by: Will Deacon <will@kernel.org>
---
 .../admin-guide/kernel-parameters.txt         |   3 +
 Documentation/arm64/asymmetric-32bit.rst      | 155 ++++++++++++++++++
 Documentation/arm64/index.rst                 |   1 +
 3 files changed, 159 insertions(+)
 create mode 100644 Documentation/arm64/asymmetric-32bit.rst

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a2e453919bb6..5a1dc7e628a5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -295,6 +295,9 @@
 			EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
 			and hot-unplug operations may be restricted.
 
+			See Documentation/arm64/asymmetric-32bit.rst for more
+			information.
+
 	amd_iommu=	[HW,X86-64]
 			Pass parameters to the AMD IOMMU driver in the system.
 			Possible values are:
diff --git a/Documentation/arm64/asymmetric-32bit.rst b/Documentation/arm64/asymmetric-32bit.rst
new file mode 100644
index 000000000000..64a0b505da7d
--- /dev/null
+++ b/Documentation/arm64/asymmetric-32bit.rst
@@ -0,0 +1,155 @@
+======================
+Asymmetric 32-bit SoCs
+======================
+
+Author: Will Deacon <will@kernel.org>
+
+This document describes the impact of asymmetric 32-bit SoCs on the
+execution of 32-bit (``AArch32``) applications.
+
+Date: 2021-05-17
+
+Introduction
+============
+
+Some Armv9 SoCs suffer from a big.LITTLE misfeature where only a subset
+of the CPUs are capable of executing 32-bit user applications. On such
+a system, Linux by default treats the asymmetry as a "mismatch" and
+disables support for both the ``PER_LINUX32`` personality and
+``execve(2)`` of 32-bit ELF binaries, with the latter returning
+``-ENOEXEC``. If the mismatch is detected during late onlining of a
+64-bit-only CPU, then the onlining operation fails and the new CPU is
+unavailable for scheduling.
+
+Surprisingly, these SoCs have been produced with the intention of
+running legacy 32-bit binaries. Unsurprisingly, that doesn't work very
+well with the default behaviour of Linux.
+
+It seems inevitable that future SoCs will drop 32-bit support
+altogether, so if you're stuck in the unenviable position of needing to
+run 32-bit code on one of these transitionary platforms then you would
+be wise to consider alternatives such as recompilation, emulation or
+retirement. If neither of those options are practical, then read on.
+
+Enabling kernel support
+=======================
+
+Since the kernel support is not completely transparent to userspace,
+allowing 32-bit tasks to run on an asymmetric 32-bit system requires an
+explicit "opt-in" and can be enabled by passing the
+``allow_mismatched_32bit_el0`` parameter on the kernel command-line.
+
+For the remainder of this document we will refer to an *asymmetric
+system* to mean an asymmetric 32-bit SoC running Linux with this kernel
+command-line option enabled.
+
+Userspace impact
+================
+
+32-bit tasks running on an asymmetric system behave in mostly the same
+way as on a homogeneous system, with a few key differences relating to
+CPU affinity.
+
+sysfs
+-----
+
+The subset of CPUs capable of running 32-bit tasks is described in
+``/sys/devices/system/cpu/aarch32_el0`` and is documented further in
+``Documentation/ABI/testing/sysfs-devices-system-cpu``.
+
+**Note:** CPUs are advertised by this file as they are detected and so
+late-onlining of 32-bit-capable CPUs can result in the file contents
+being modified by the kernel at runtime. Once advertised, CPUs are never
+removed from the file.
+
+``execve(2)``
+-------------
+
+On a homogeneous system, the CPU affinity of a task is preserved across
+``execve(2)``. This is not always possible on an asymmetric system,
+specifically when the new program being executed is 32-bit yet the
+affinity mask contains 64-bit-only CPUs. In this situation, the kernel
+determines the new affinity mask as follows:
+
+  1. If the 32-bit-capable subset of the affinity mask is not empty,
+     then the affinity is restricted to that subset and the old affinity
+     mask is saved. This saved mask is inherited over ``fork(2)`` and
+     preserved across ``execve(2)`` of 32-bit programs.
+
+     **Note:** This step does not apply to ``SCHED_DEADLINE`` tasks.
+     See `SCHED_DEADLINE`_.
+
+  2. Otherwise, the cpuset hierarchy of the task is walked until an
+     ancestor is found containing at least one 32-bit-capable CPU. The
+     affinity of the task is then changed to match the 32-bit-capable
+     subset of the cpuset determined by the walk.
+
+  3. On failure (i.e. out of memory), the affinity is changed to the set
+     of all 32-bit-capable CPUs of which the kernel is aware.
+
+A subsequent ``execve(2)`` of a 64-bit program by the 32-bit task will
+invalidate the affinity mask saved in (1) and attempt to restore the CPU
+affinity of the task using the saved mask if it was previously valid.
+This restoration may fail due to intervening changes to the deadline
+policy or cpuset hierarchy, in which case the ``execve(2)`` continues
+with the affinity unchanged.
+
+Calls to ``sched_setaffinity(2)`` for a 32-bit task will consider only
+the 32-bit-capable CPUs of the requested affinity mask. On success, the
+affinity for the task is updated and any saved mask from a prior
+``execve(2)`` is invalidated.
+
+``SCHED_DEADLINE``
+------------------
+
+Explicit admission of a 32-bit deadline task to the default root domain
+(e.g. by calling ``sched_setattr(2)``) is rejected on an asymmetric
+32-bit system unless admission control is disabled by writing -1 to
+``/proc/sys/kernel/sched_rt_runtime_us``.
+
+``execve(2)`` of a 32-bit program from a 64-bit deadline task will
+return ``-ENOEXEC`` if the root domain for the task contains any
+64-bit-only CPUs and admission control is enabled. Concurrent offlining
+of 32-bit-capable CPUs may still necessitate the procedure described in
+`execve(2)`_, in which case step (1) is skipped and a warning is
+emitted on the console.
+
+**Note:** It is recommended that a set of 32-bit-capable CPUs are placed
+into a separate root domain if ``SCHED_DEADLINE`` is to be used with
+32-bit tasks on an asymmetric system. Failure to do so is likely to
+result in missed deadlines.
+
+Cpusets
+-------
+
+The affinity of a 32-bit task on an asymmetric system may include CPUs
+that are not explicitly allowed by the cpuset to which it is attached.
+This can occur as a result of the following two situations:
+
+  - A 64-bit task attached to a cpuset which allows only 64-bit CPUs
+    executes a 32-bit program.
+
+  - All of the 32-bit-capable CPUs allowed by a cpuset containing a
+    32-bit task are offlined.
+
+In both of these cases, the new affinity is calculated according to step
+(2) of the process described in `execve(2)`_ and the cpuset hierarchy is
+unchanged irrespective of the cgroup version.
+
+CPU hotplug
+-----------
+
+On an asymmetric system, the first detected 32-bit-capable CPU is
+prevented from being offlined by userspace and any such attempt will
+return ``-EPERM``. Note that suspend is still permitted even if the
+primary CPU (i.e. CPU 0) is 64-bit-only.
+
+KVM
+---
+
+Although KVM will not advertise 32-bit EL0 support to any vCPUs on an
+asymmetric system, a broken guest at EL1 could still attempt to execute
+32-bit code at EL0. In this case, an exit from a vCPU thread in 32-bit
+mode will return to host userspace with an ``exit_reason`` of
+``KVM_EXIT_FAIL_ENTRY`` and will remain non-runnable until successfully
+re-initialised by a subsequent ``KVM_ARM_VCPU_INIT`` operation.
diff --git a/Documentation/arm64/index.rst b/Documentation/arm64/index.rst
index 97d65ba12a35..4f840bac083e 100644
--- a/Documentation/arm64/index.rst
+++ b/Documentation/arm64/index.rst
@@ -10,6 +10,7 @@ ARM64 Architecture
     acpi_object_usage
     amu
     arm-acpi
+    asymmetric-32bit
     booting
     cpu-feature-registers
     elf_hwcaps
-- 
2.32.0.93.g670b81a890-goog

[PATCH v10 16/16] Documentation: arm64: describe asymmetric 32-bit support

[Will Deacon]

Document support for running 32-bit tasks on asymmetric 32-bit systems
and its impact on the user ABI when enabled.

Signed-off-by: Will Deacon <will@kernel.org>
---
 .../admin-guide/kernel-parameters.txt         |   3 +
 Documentation/arm64/asymmetric-32bit.rst      | 155 ++++++++++++++++++
 Documentation/arm64/index.rst                 |   1 +
 3 files changed, 159 insertions(+)
 create mode 100644 Documentation/arm64/asymmetric-32bit.rst

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a2e453919bb6..5a1dc7e628a5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -295,6 +295,9 @@
 			EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
 			and hot-unplug operations may be restricted.
 
+			See Documentation/arm64/asymmetric-32bit.rst for more
+			information.
+
 	amd_iommu=	[HW,X86-64]
 			Pass parameters to the AMD IOMMU driver in the system.
 			Possible values are:
diff --git a/Documentation/arm64/asymmetric-32bit.rst b/Documentation/arm64/asymmetric-32bit.rst
new file mode 100644
index 000000000000..64a0b505da7d
--- /dev/null
+++ b/Documentation/arm64/asymmetric-32bit.rst
@@ -0,0 +1,155 @@
+======================
+Asymmetric 32-bit SoCs
+======================
+
+Author: Will Deacon <will@kernel.org>
+
+This document describes the impact of asymmetric 32-bit SoCs on the
+execution of 32-bit (``AArch32``) applications.
+
+Date: 2021-05-17
+
+Introduction
+============
+
+Some Armv9 SoCs suffer from a big.LITTLE misfeature where only a subset
+of the CPUs are capable of executing 32-bit user applications. On such
+a system, Linux by default treats the asymmetry as a "mismatch" and
+disables support for both the ``PER_LINUX32`` personality and
+``execve(2)`` of 32-bit ELF binaries, with the latter returning
+``-ENOEXEC``. If the mismatch is detected during late onlining of a
+64-bit-only CPU, then the onlining operation fails and the new CPU is
+unavailable for scheduling.
+
+Surprisingly, these SoCs have been produced with the intention of
+running legacy 32-bit binaries. Unsurprisingly, that doesn't work very
+well with the default behaviour of Linux.
+
+It seems inevitable that future SoCs will drop 32-bit support
+altogether, so if you're stuck in the unenviable position of needing to
+run 32-bit code on one of these transitionary platforms then you would
+be wise to consider alternatives such as recompilation, emulation or
+retirement. If neither of those options are practical, then read on.
+
+Enabling kernel support
+=======================
+
+Since the kernel support is not completely transparent to userspace,
+allowing 32-bit tasks to run on an asymmetric 32-bit system requires an
+explicit "opt-in" and can be enabled by passing the
+``allow_mismatched_32bit_el0`` parameter on the kernel command-line.
+
+For the remainder of this document we will refer to an *asymmetric
+system* to mean an asymmetric 32-bit SoC running Linux with this kernel
+command-line option enabled.
+
+Userspace impact
+================
+
+32-bit tasks running on an asymmetric system behave in mostly the same
+way as on a homogeneous system, with a few key differences relating to
+CPU affinity.
+
+sysfs
+-----
+
+The subset of CPUs capable of running 32-bit tasks is described in
+``/sys/devices/system/cpu/aarch32_el0`` and is documented further in
+``Documentation/ABI/testing/sysfs-devices-system-cpu``.
+
+**Note:** CPUs are advertised by this file as they are detected and so
+late-onlining of 32-bit-capable CPUs can result in the file contents
+being modified by the kernel at runtime. Once advertised, CPUs are never
+removed from the file.
+
+``execve(2)``
+-------------
+
+On a homogeneous system, the CPU affinity of a task is preserved across
+``execve(2)``. This is not always possible on an asymmetric system,
+specifically when the new program being executed is 32-bit yet the
+affinity mask contains 64-bit-only CPUs. In this situation, the kernel
+determines the new affinity mask as follows:
+
+  1. If the 32-bit-capable subset of the affinity mask is not empty,
+     then the affinity is restricted to that subset and the old affinity
+     mask is saved. This saved mask is inherited over ``fork(2)`` and
+     preserved across ``execve(2)`` of 32-bit programs.
+
+     **Note:** This step does not apply to ``SCHED_DEADLINE`` tasks.
+     See `SCHED_DEADLINE`_.
+
+  2. Otherwise, the cpuset hierarchy of the task is walked until an
+     ancestor is found containing at least one 32-bit-capable CPU. The
+     affinity of the task is then changed to match the 32-bit-capable
+     subset of the cpuset determined by the walk.
+
+  3. On failure (i.e. out of memory), the affinity is changed to the set
+     of all 32-bit-capable CPUs of which the kernel is aware.
+
+A subsequent ``execve(2)`` of a 64-bit program by the 32-bit task will
+invalidate the affinity mask saved in (1) and attempt to restore the CPU
+affinity of the task using the saved mask if it was previously valid.
+This restoration may fail due to intervening changes to the deadline
+policy or cpuset hierarchy, in which case the ``execve(2)`` continues
+with the affinity unchanged.
+
+Calls to ``sched_setaffinity(2)`` for a 32-bit task will consider only
+the 32-bit-capable CPUs of the requested affinity mask. On success, the
+affinity for the task is updated and any saved mask from a prior
+``execve(2)`` is invalidated.
+
+``SCHED_DEADLINE``
+------------------
+
+Explicit admission of a 32-bit deadline task to the default root domain
+(e.g. by calling ``sched_setattr(2)``) is rejected on an asymmetric
+32-bit system unless admission control is disabled by writing -1 to
+``/proc/sys/kernel/sched_rt_runtime_us``.
+
+``execve(2)`` of a 32-bit program from a 64-bit deadline task will
+return ``-ENOEXEC`` if the root domain for the task contains any
+64-bit-only CPUs and admission control is enabled. Concurrent offlining
+of 32-bit-capable CPUs may still necessitate the procedure described in
+`execve(2)`_, in which case step (1) is skipped and a warning is
+emitted on the console.
+
+**Note:** It is recommended that a set of 32-bit-capable CPUs are placed
+into a separate root domain if ``SCHED_DEADLINE`` is to be used with
+32-bit tasks on an asymmetric system. Failure to do so is likely to
+result in missed deadlines.
+
+Cpusets
+-------
+
+The affinity of a 32-bit task on an asymmetric system may include CPUs
+that are not explicitly allowed by the cpuset to which it is attached.
+This can occur as a result of the following two situations:
+
+  - A 64-bit task attached to a cpuset which allows only 64-bit CPUs
+    executes a 32-bit program.
+
+  - All of the 32-bit-capable CPUs allowed by a cpuset containing a
+    32-bit task are offlined.
+
+In both of these cases, the new affinity is calculated according to step
+(2) of the process described in `execve(2)`_ and the cpuset hierarchy is
+unchanged irrespective of the cgroup version.
+
+CPU hotplug
+-----------
+
+On an asymmetric system, the first detected 32-bit-capable CPU is
+prevented from being offlined by userspace and any such attempt will
+return ``-EPERM``. Note that suspend is still permitted even if the
+primary CPU (i.e. CPU 0) is 64-bit-only.
+
+KVM
+---
+
+Although KVM will not advertise 32-bit EL0 support to any vCPUs on an
+asymmetric system, a broken guest at EL1 could still attempt to execute
+32-bit code at EL0. In this case, an exit from a vCPU thread in 32-bit
+mode will return to host userspace with an ``exit_reason`` of
+``KVM_EXIT_FAIL_ENTRY`` and will remain non-runnable until successfully
+re-initialised by a subsequent ``KVM_ARM_VCPU_INIT`` operation.
diff --git a/Documentation/arm64/index.rst b/Documentation/arm64/index.rst
index 97d65ba12a35..4f840bac083e 100644
--- a/Documentation/arm64/index.rst
+++ b/Documentation/arm64/index.rst
@@ -10,6 +10,7 @@ ARM64 Architecture
     acpi_object_usage
     amu
     arm-acpi
+    asymmetric-32bit
     booting
     cpu-feature-registers
     elf_hwcaps
-- 
2.32.0.93.g670b81a890-goog


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