Merge tag 'sched-urgent-2026-05-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:

 - Fix spurious failures in rseq self-tests (Mark Brown)

 - Fix rseq rseq::cpu_id_start ABI regression due to TCMalloc's creative
   use of the supposedly read-only field

   The fix is to introduce a new ABI variant based on a new (larger)
   rseq area registration size, to keep the TCMalloc use of rseq
   backwards compatible on new kernels (Thomas Gleixner)

 - Fix wakeup_preempt_fair() for not waking up task (Vincent Guittot)

 - Fix s64 mult overflow in vruntime_eligible() (Zhan Xusheng)

* tag 'sched-urgent-2026-05-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Fix wakeup_preempt_fair() for not waking up task
  sched/fair: Fix overflow in vruntime_eligible()
  selftests/rseq: Expand for optimized RSEQ ABI v2
  rseq: Reenable performance optimizations conditionally
  rseq: Implement read only ABI enforcement for optimized RSEQ V2 mode
  selftests/rseq: Validate legacy behavior
  selftests/rseq: Make registration flexible for legacy and optimized mode
  selftests/rseq: Skip tests if time slice extensions are not available
  rseq: Revert to historical performance killing behaviour
  rseq: Don't advertise time slice extensions if disabled
  rseq: Protect rseq_reset() against interrupts
  rseq: Set rseq::cpu_id_start to 0 on unregistration
  selftests/rseq: Don't run tests with runner scripts outside of the scripts

19 files changed, 580 insertions, 211 deletions

diff --git a/Documentation/userspace-api/rseq.rst b/Documentation/userspace-api/rseq.rst
index 3cd27a3c7c7e..8549a6c61531 100644
--- a/Documentation/userspace-api/rseq.rst
+++ b/Documentation/userspace-api/rseq.rst
@@ -24,6 +24,97 @@ Quick access to CPU number, node ID
 Allows to implement per CPU data efficiently. Documentation is in code and
 selftests. :(
 
+Optimized RSEQ V2
+-----------------
+
+On architectures which utilize the generic entry code and generic TIF bits
+the kernel supports runtime optimizations for RSEQ, which also enable
+enhanced features like scheduler time slice extensions.
+
+To enable them a task has to register the RSEQ region with at least the
+length advertised by getauxval(AT_RSEQ_FEATURE_SIZE).
+
+If existing binaries register with RSEQ_ORIG_SIZE (32 bytes), the kernel
+keeps the legacy low performance mode enabled to fulfil the expectations
+of existing users regarding the original RSEQ implementation behaviour.
+
+The following table documents the ABI and behavioral guarantees of the
+legacy and the optimized V2 mode.
+
+.. list-table:: RSEQ modes
+   :header-rows: 1
+
+   * - Nr
+     - What
+
+     - Legacy
+     - Optimized V2
+
+   * - 1
+     - The cpu_id_start, cpu_id, node_id and mm_cid fields (User mode read
+       only)
+       .. Legacy
+     - Updated by the kernel unconditionally after each context switch and
+       before signal delivery
+       .. Optimized V2
+     - Updated by the kernel if and only if they change, i.e. if the task
+       is migrated or mm_cid changes
+
+   * - 2
+     - The rseq_cs critical section field
+       .. Legacy
+     - Evaluated and handled unconditionally after each context switch and
+       before signal delivery
+       .. Optimized V2
+     - Evaluated and handled conditionally only when user space was
+       interrupted and was scheduled out or before delivering a signal in
+       the interrupted context.
+
+   * - 3
+     - Read only fields
+       .. Legacy
+     - No strict enforcement except in debug mode
+       .. Optimized V2
+     - Strict enforcement
+
+   * - 4
+     - membarrier(...RSEQ)
+       .. Legacy
+     - All running threads of the process are interrupted and the ID fields
+       are rewritten and eventually active critical sections are aborted
+       before they return to user space.  All threads which are scheduled
+       out whether voluntary or not are covered by #1/#2 above.
+       .. Optimized V2
+     - All running threads of the process are interrupted and eventually
+       active critical sections are aborted before these threads return to
+       user space. The ID fields are only updated if changed as a
+       consequence of the interrupt. All threads which are scheduled out
+       whether voluntary or not are covered by #1/#2 above.
+
+   * - 5
+     - Time slice extensions
+       .. Legacy
+     - Not supported
+       .. Optimized V2
+     - Supported
+
+The legacy mode is obviously less performant as it does unconditional
+updates and critical section checks even if not strictly required by the
+ABI contract. That can't be changed anymore as some users depend on that
+observed behavior, which in turn enables them to violate the ABI and
+overwrite the cpu_id_start field for their own purposes. This is obviously
+discouraged as it renders RSEQ incompatible with the intended usage and
+breaks the expectation of other libraries in the same application.
+
+The ABI compliant optimized v2 mode, which respects the read only fields,
+does not require unconditional updates and therefore is way more
+performant. The kernel validates the read only fields for compliance. If
+user space modifies them, the process is killed. Compliant usage allows
+multiple libraries in the same application to benefit from the RSEQ
+functionality without disturbing each other. The ABI compliant optimized v2
+mode also enables extended RSEQ features like time slice extensions.
+
+
 Scheduler time slice extensions
 -------------------------------
 
@@ -37,7 +128,8 @@ The prerequisites for this functionality are:
 
     * Enabled at boot time (default is enabled)
 
-    * A rseq userspace pointer has been registered for the thread
+    * A rseq userspace pointer has been registered for the thread in
+      optimized V2 mode
 
 The thread has to enable the functionality via prctl(2)::
 
diff --git a/include/linux/rseq.h b/include/linux/rseq.h
index b9d62fc2140d..7ef79b25e714 100644
--- a/include/linux/rseq.h
+++ b/include/linux/rseq.h
@@ -9,6 +9,11 @@
 
 void __rseq_handle_slowpath(struct pt_regs *regs);
 
+static __always_inline bool rseq_v2(struct task_struct *t)
+{
+	return IS_ENABLED(CONFIG_GENERIC_IRQ_ENTRY) && likely(t->rseq.event.has_rseq > 1);
+}
+
 /* Invoked from resume_user_mode_work() */
 static inline void rseq_handle_slowpath(struct pt_regs *regs)
 {
@@ -16,8 +21,7 @@ static inline void rseq_handle_slowpath(struct pt_regs *regs)
 		if (current->rseq.event.slowpath)
 			__rseq_handle_slowpath(regs);
 	} else {
-		/* '&' is intentional to spare one conditional branch */
-		if (current->rseq.event.sched_switch & current->rseq.event.has_rseq)
+		if (current->rseq.event.sched_switch && current->rseq.event.has_rseq)
 			__rseq_handle_slowpath(regs);
 	}
 }
@@ -30,9 +34,9 @@ void __rseq_signal_deliver(int sig, struct pt_regs *regs);
  */
 static inline void rseq_signal_deliver(struct ksignal *ksig, struct pt_regs *regs)
 {
-	if (IS_ENABLED(CONFIG_GENERIC_IRQ_ENTRY)) {
-		/* '&' is intentional to spare one conditional branch */
-		if (current->rseq.event.has_rseq & current->rseq.event.user_irq)
+	if (rseq_v2(current)) {
+		/* has_rseq is implied in rseq_v2() */
+		if (current->rseq.event.user_irq)
 			__rseq_signal_deliver(ksig->sig, regs);
 	} else {
 		if (current->rseq.event.has_rseq)
@@ -50,15 +54,22 @@ static __always_inline void rseq_sched_switch_event(struct task_struct *t)
 {
 	struct rseq_event *ev = &t->rseq.event;
 
-	if (IS_ENABLED(CONFIG_GENERIC_IRQ_ENTRY)) {
+	/*
+	 * Only apply the user_irq optimization for RSEQ ABI V2 registrations.
+	 * Legacy users like TCMalloc rely on the original ABI V1 behaviour
+	 * which updates IDs on every context swtich.
+	 */
+	if (rseq_v2(t)) {
 		/*
-		 * Avoid a boat load of conditionals by using simple logic
-		 * to determine whether NOTIFY_RESUME needs to be raised.
+		 * Avoid a boat load of conditionals by using simple logic to
+		 * determine whether TIF_NOTIFY_RESUME or TIF_RSEQ needs to be
+		 * raised.
 		 *
-		 * It's required when the CPU or MM CID has changed or
-		 * the entry was from user space.
+		 * It's required when the CPU or MM CID has changed or the entry
+		 * was via interrupt from user space. ev->has_rseq does not have
+		 * to be evaluated here because rseq_v2() implies has_rseq.
 		 */
-		bool raise = (ev->user_irq | ev->ids_changed) & ev->has_rseq;
+		bool raise = ev->user_irq | ev->ids_changed;
 
 		if (raise) {
 			ev->sched_switch = true;
@@ -66,6 +77,7 @@ static __always_inline void rseq_sched_switch_event(struct task_struct *t)
 		}
 	} else {
 		if (ev->has_rseq) {
+			t->rseq.event.ids_changed = true;
 			t->rseq.event.sched_switch = true;
 			rseq_raise_notify_resume(t);
 		}
@@ -119,6 +131,8 @@ static inline void rseq_virt_userspace_exit(void)
 
 static inline void rseq_reset(struct task_struct *t)
 {
+	/* Protect against preemption and membarrier IPI */
+	guard(irqsave)();
 	memset(&t->rseq, 0, sizeof(t->rseq));
 	t->rseq.ids.cpu_id = RSEQ_CPU_ID_UNINITIALIZED;
 }
@@ -159,6 +173,7 @@ static inline unsigned int rseq_alloc_align(void)
 }
 
 #else /* CONFIG_RSEQ */
+static inline bool rseq_v2(struct task_struct *t) { return false; }
 static inline void rseq_handle_slowpath(struct pt_regs *regs) { }
 static inline void rseq_signal_deliver(struct ksignal *ksig, struct pt_regs *regs) { }
 static inline void rseq_sched_switch_event(struct task_struct *t) { }
diff --git a/include/linux/rseq_entry.h b/include/linux/rseq_entry.h
index f11ebd34f8b9..2d0295df5107 100644
--- a/include/linux/rseq_entry.h
+++ b/include/linux/rseq_entry.h
@@ -111,6 +111,20 @@ static __always_inline void rseq_slice_clear_grant(struct task_struct *t)
 	t->rseq.slice.state.granted = false;
 }
 
+/*
+ * Open coded, so it can be invoked within a user access region.
+ *
+ * This clears the user space state of the time slice extensions field only when
+ * the task has registered the optimized RSEQ_ABI V2. Some legacy registrations,
+ * e.g. TCMalloc, have conflicting non-ABI fields in struct RSEQ, which would be
+ * overwritten by an unconditional write.
+ */
+#define rseq_slice_clear_user(rseq, efault)				\
+do {									\
+	if (rseq_slice_extension_enabled())				\
+		unsafe_put_user(0U, &rseq->slice_ctrl.all, efault);	\
+} while (0)
+
 static __always_inline bool __rseq_grant_slice_extension(bool work_pending)
 {
 	struct task_struct *curr = current;
@@ -230,10 +244,10 @@ static __always_inline bool rseq_slice_extension_enabled(void) { return false; }
 static __always_inline bool rseq_arm_slice_extension_timer(void) { return false; }
 static __always_inline void rseq_slice_clear_grant(struct task_struct *t) { }
 static __always_inline bool rseq_grant_slice_extension(unsigned long ti_work, unsigned long mask) { return false; }
+#define rseq_slice_clear_user(rseq, efault) do { } while (0)
 #endif /* !CONFIG_RSEQ_SLICE_EXTENSION */
 
 bool rseq_debug_update_user_cs(struct task_struct *t, struct pt_regs *regs, unsigned long csaddr);
-bool rseq_debug_validate_ids(struct task_struct *t);
 
 static __always_inline void rseq_note_user_irq_entry(void)
 {
@@ -353,43 +367,6 @@ efault:
 	return false;
 }
 
-/*
- * On debug kernels validate that user space did not mess with it if the
- * debug branch is enabled.
- */
-bool rseq_debug_validate_ids(struct task_struct *t)
-{
-	struct rseq __user *rseq = t->rseq.usrptr;
-	u32 cpu_id, uval, node_id;
-
-	/*
-	 * On the first exit after registering the rseq region CPU ID is
-	 * RSEQ_CPU_ID_UNINITIALIZED and node_id in user space is 0!
-	 */
-	node_id = t->rseq.ids.cpu_id != RSEQ_CPU_ID_UNINITIALIZED ?
-		  cpu_to_node(t->rseq.ids.cpu_id) : 0;
-
-	scoped_user_read_access(rseq, efault) {
-		unsafe_get_user(cpu_id, &rseq->cpu_id_start, efault);
-		if (cpu_id != t->rseq.ids.cpu_id)
-			goto die;
-		unsafe_get_user(uval, &rseq->cpu_id, efault);
-		if (uval != cpu_id)
-			goto die;
-		unsafe_get_user(uval, &rseq->node_id, efault);
-		if (uval != node_id)
-			goto die;
-		unsafe_get_user(uval, &rseq->mm_cid, efault);
-		if (uval != t->rseq.ids.mm_cid)
-			goto die;
-	}
-	return true;
-die:
-	t->rseq.event.fatal = true;
-efault:
-	return false;
-}
-
 #endif /* RSEQ_BUILD_SLOW_PATH */
 
 /*
@@ -499,37 +476,50 @@ efault:
  * faults in task context are fatal too.
  */
 static rseq_inline
-bool rseq_set_ids_get_csaddr(struct task_struct *t, struct rseq_ids *ids,
-			     u32 node_id, u64 *csaddr)
+bool rseq_set_ids_get_csaddr(struct task_struct *t, struct rseq_ids *ids, u64 *csaddr)
 {
 	struct rseq __user *rseq = t->rseq.usrptr;
 
-	if (static_branch_unlikely(&rseq_debug_enabled)) {
-		if (!rseq_debug_validate_ids(t))
-			return false;
-	}
-
 	scoped_user_rw_access(rseq, efault) {
+		/* Validate the R/O fields for debug and optimized mode */
+		if (static_branch_unlikely(&rseq_debug_enabled) || rseq_v2(t)) {
+			u32 cpu_id, uval;
+
+			unsafe_get_user(cpu_id, &rseq->cpu_id_start, efault);
+			if (cpu_id != t->rseq.ids.cpu_id)
+				goto die;
+			unsafe_get_user(uval, &rseq->cpu_id, efault);
+			if (uval != cpu_id)
+				goto die;
+			unsafe_get_user(uval, &rseq->node_id, efault);
+			if (uval != t->rseq.ids.node_id)
+				goto die;
+			unsafe_get_user(uval, &rseq->mm_cid, efault);
+			if (uval != t->rseq.ids.mm_cid)
+				goto die;
+		}
+
 		unsafe_put_user(ids->cpu_id, &rseq->cpu_id_start, efault);
 		unsafe_put_user(ids->cpu_id, &rseq->cpu_id, efault);
-		unsafe_put_user(node_id, &rseq->node_id, efault);
+		unsafe_put_user(ids->node_id, &rseq->node_id, efault);
 		unsafe_put_user(ids->mm_cid, &rseq->mm_cid, efault);
 		if (csaddr)
 			unsafe_get_user(*csaddr, &rseq->rseq_cs, efault);
 
-		/* Open coded, so it's in the same user access region */
-		if (rseq_slice_extension_enabled()) {
-			/* Unconditionally clear it, no point in conditionals */
-			unsafe_put_user(0U, &rseq->slice_ctrl.all, efault);
-		}
+		/* RSEQ ABI V2 only operations */
+		if (rseq_v2(t))
+			rseq_slice_clear_user(rseq, efault);
 	}
 
 	rseq_slice_clear_grant(t);
 	/* Cache the new values */
-	t->rseq.ids.cpu_cid = ids->cpu_cid;
+	t->rseq.ids = *ids;
 	rseq_stat_inc(rseq_stats.ids);
 	rseq_trace_update(t, ids);
 	return true;
+
+die:
+	t->rseq.event.fatal = true;
 efault:
 	return false;
 }
@@ -539,11 +529,11 @@ efault:
  * is in a critical section.
  */
 static rseq_inline bool rseq_update_usr(struct task_struct *t, struct pt_regs *regs,
-					struct rseq_ids *ids, u32 node_id)
+					struct rseq_ids *ids)
 {
 	u64 csaddr;
 
-	if (!rseq_set_ids_get_csaddr(t, ids, node_id, &csaddr))
+	if (!rseq_set_ids_get_csaddr(t, ids, &csaddr))
 		return false;
 
 	/*
@@ -612,6 +602,14 @@ static __always_inline bool rseq_exit_user_update(struct pt_regs *regs, struct t
 	 * interrupts disabled
 	 */
 	guard(pagefault)();
+	/*
+	 * This optimization is only valid when the task registered for the
+	 * optimized RSEQ_ABI_V2 variant. Some legacy users rely on the original
+	 * RSEQ implementation behaviour which unconditionally updated the IDs.
+	 * rseq_sched_switch_event() ensures that legacy registrations always
+	 * have both sched_switch and ids_changed set, which is compatible with
+	 * the historical TIF_NOTIFY_RESUME behaviour.
+	 */
 	if (likely(!t->rseq.event.ids_changed)) {
 		struct rseq __user *rseq = t->rseq.usrptr;
 		/*
@@ -623,11 +621,9 @@ static __always_inline bool rseq_exit_user_update(struct pt_regs *regs, struct t
 		scoped_user_rw_access(rseq, efault) {
 			unsafe_get_user(csaddr, &rseq->rseq_cs, efault);
 
-			/* Open coded, so it's in the same user access region */
-			if (rseq_slice_extension_enabled()) {
-				/* Unconditionally clear it, no point in conditionals */
-				unsafe_put_user(0U, &rseq->slice_ctrl.all, efault);
-			}
+			/* RSEQ ABI V2 only operations */
+			if (rseq_v2(t))
+				rseq_slice_clear_user(rseq, efault);
 		}
 
 		rseq_slice_clear_grant(t);
@@ -640,12 +636,12 @@ static __always_inline bool rseq_exit_user_update(struct pt_regs *regs, struct t
 	}
 
 	struct rseq_ids ids = {
-		.cpu_id = task_cpu(t),
-		.mm_cid = task_mm_cid(t),
+		.cpu_id	 = task_cpu(t),
+		.mm_cid	 = task_mm_cid(t),
+		.node_id = cpu_to_node(ids.cpu_id),
 	};
-	u32 node_id = cpu_to_node(ids.cpu_id);
 
-	return rseq_update_usr(t, regs, &ids, node_id);
+	return rseq_update_usr(t, regs, &ids);
 efault:
 	return false;
 }
diff --git a/include/linux/rseq_types.h b/include/linux/rseq_types.h
index 0b42045988db..85739a63e85e 100644
--- a/include/linux/rseq_types.h
+++ b/include/linux/rseq_types.h
@@ -9,6 +9,12 @@
 #ifdef CONFIG_RSEQ
 struct rseq;
 
+/*
+ * rseq_event::has_rseq contains the ABI version number so preserving it
+ * in AND operations requires a mask.
+ */
+#define RSEQ_HAS_RSEQ_VERSION_MASK	0xff
+
 /**
  * struct rseq_event - Storage for rseq related event management
  * @all:		Compound to initialize and clear the data efficiently
@@ -17,7 +23,8 @@ struct rseq;
  *			exit to user
  * @ids_changed:	Indicator that IDs need to be updated
  * @user_irq:		True on interrupt entry from user mode
- * @has_rseq:		True if the task has a rseq pointer installed
+ * @has_rseq:		Greater than 0 if the task has a rseq pointer installed.
+ *			Contains the RSEQ version number
  * @error:		Compound error code for the slow path to analyze
  * @fatal:		User space data corrupted or invalid
  * @slowpath:		Indicator that slow path processing via TIF_NOTIFY_RESUME
@@ -59,8 +66,9 @@ struct rseq_event {
  *		compiler emit a single compare on 64-bit
  * @cpu_id:	The CPU ID which was written last to user space
  * @mm_cid:	The MM CID which was written last to user space
+ * @node_id:	The node ID which was written last to user space
  *
- * @cpu_id and @mm_cid are updated when the data is written to user space.
+ * @cpu_id, @mm_cid and @node_id are updated when the data is written to user space.
  */
 struct rseq_ids {
 	union {
@@ -70,6 +78,7 @@ struct rseq_ids {
 			u32	mm_cid;
 		};
 	};
+	u32			node_id;
 };
 
 /**
diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index f69344fe6c08..ca6fe1f9d05e 100644
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -28,7 +28,7 @@ enum rseq_cs_flags_bit {
 	RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT_BIT	= 0,
 	RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL_BIT	= 1,
 	RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT	= 2,
-	/* (3) Intentional gap to put new bits into a separate byte */
+	/* (3) Intentional gap to keep new bits separate */
 
 	/* User read only feature flags */
 	RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE_BIT	= 4,
@@ -161,6 +161,9 @@ struct rseq {
 	 *	- RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT
 	 *	- RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL
 	 *	- RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE
+	 *
+	 * It is now used for feature status advertisement by the kernel.
+	 * See: enum rseq_cs_flags_bit for further information.
 	 */
 	__u32 flags;
 
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 38d3ef540760..e75e3a5e312c 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -236,11 +236,6 @@ static int __init rseq_debugfs_init(void)
 }
 __initcall(rseq_debugfs_init);
 
-static bool rseq_set_ids(struct task_struct *t, struct rseq_ids *ids, u32 node_id)
-{
-	return rseq_set_ids_get_csaddr(t, ids, node_id, NULL);
-}
-
 static bool rseq_handle_cs(struct task_struct *t, struct pt_regs *regs)
 {
 	struct rseq __user *urseq = t->rseq.usrptr;
@@ -258,14 +253,16 @@ efault:
 static void rseq_slowpath_update_usr(struct pt_regs *regs)
 {
 	/*
-	 * Preserve rseq state and user_irq state. The generic entry code
-	 * clears user_irq on the way out, the non-generic entry
-	 * architectures are not having user_irq.
+	 * Preserve has_rseq and user_irq state. The generic entry code clears
+	 * user_irq on the way out, the non-generic entry architectures are not
+	 * setting user_irq.
 	 */
-	const struct rseq_event evt_mask = { .has_rseq = true, .user_irq = true, };
+	const struct rseq_event evt_mask = {
+		.has_rseq	= RSEQ_HAS_RSEQ_VERSION_MASK,
+		.user_irq	= true,
+	};
 	struct task_struct *t = current;
 	struct rseq_ids ids;
-	u32 node_id;
 	bool event;
 
 	if (unlikely(t->flags & PF_EXITING))
@@ -301,9 +298,9 @@ static void rseq_slowpath_update_usr(struct pt_regs *regs)
 	if (!event)
 		return;
 
-	node_id = cpu_to_node(ids.cpu_id);
+	ids.node_id = cpu_to_node(ids.cpu_id);
 
-	if (unlikely(!rseq_update_usr(t, regs, &ids, node_id))) {
+	if (unlikely(!rseq_update_usr(t, regs, &ids))) {
 		/*
 		 * Clear the errors just in case this might survive magically, but
 		 * leave the rest intact.
@@ -335,8 +332,9 @@ void __rseq_handle_slowpath(struct pt_regs *regs)
 void __rseq_signal_deliver(int sig, struct pt_regs *regs)
 {
 	rseq_stat_inc(rseq_stats.signal);
+
 	/*
-	 * Don't update IDs, they are handled on exit to user if
+	 * Don't update IDs yet, they are handled on exit to user if
 	 * necessary. The important thing is to abort a critical section of
 	 * the interrupted context as after this point the instruction
 	 * pointer in @regs points to the signal handler.
@@ -349,6 +347,13 @@ void __rseq_signal_deliver(int sig, struct pt_regs *regs)
 		current->rseq.event.error = 0;
 		force_sigsegv(sig);
 	}
+
+	/*
+	 * In legacy mode, force the update of IDs before returning to user
+	 * space to stay compatible.
+	 */
+	if (!rseq_v2(current))
+		rseq_force_update();
 }
 
 /*
@@ -384,19 +389,22 @@ void rseq_syscall(struct pt_regs *regs)
 
 static bool rseq_reset_ids(void)
 {
-	struct rseq_ids ids = {
-		.cpu_id		= RSEQ_CPU_ID_UNINITIALIZED,
-		.mm_cid		= 0,
-	};
+	struct rseq __user *rseq = current->rseq.usrptr;
 
 	/*
 	 * If this fails, terminate it because this leaves the kernel in
 	 * stupid state as exit to user space will try to fixup the ids
 	 * again.
 	 */
-	if (rseq_set_ids(current, &ids, 0))
-		return true;
+	scoped_user_rw_access(rseq, efault) {
+		unsafe_put_user(0, &rseq->cpu_id_start, efault);
+		unsafe_put_user(RSEQ_CPU_ID_UNINITIALIZED, &rseq->cpu_id, efault);
+		unsafe_put_user(0, &rseq->node_id, efault);
+		unsafe_put_user(0, &rseq->mm_cid, efault);
+	}
+	return true;
 
+efault:
 	force_sig(SIGSEGV);
 	return false;
 }
@@ -404,70 +412,29 @@ static bool rseq_reset_ids(void)
 /* The original rseq structure size (including padding) is 32 bytes. */
 #define ORIG_RSEQ_SIZE		32
 
-/*
- * sys_rseq - setup restartable sequences for caller thread.
- */
-SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32, sig)
+static long rseq_register(struct rseq __user * rseq, u32 rseq_len, int flags, u32 sig)
 {
 	u32 rseqfl = 0;
+	u8 version = 1;
 
-	if (flags & RSEQ_FLAG_UNREGISTER) {
-		if (flags & ~RSEQ_FLAG_UNREGISTER)
-			return -EINVAL;
-		/* Unregister rseq for current thread. */
-		if (current->rseq.usrptr != rseq || !current->rseq.usrptr)
-			return -EINVAL;
-		if (rseq_len != current->rseq.len)
-			return -EINVAL;
-		if (current->rseq.sig != sig)
-			return -EPERM;
-		if (!rseq_reset_ids())
-			return -EFAULT;
-		rseq_reset(current);
-		return 0;
-	}
-
-	if (unlikely(flags & ~(RSEQ_FLAG_SLICE_EXT_DEFAULT_ON)))
-		return -EINVAL;
-
-	if (current->rseq.usrptr) {
-		/*
-		 * If rseq is already registered, check whether
-		 * the provided address differs from the prior
-		 * one.
-		 */
-		if (current->rseq.usrptr != rseq || rseq_len != current->rseq.len)
-			return -EINVAL;
-		if (current->rseq.sig != sig)
-			return -EPERM;
-		/* Already registered. */
-		return -EBUSY;
-	}
-
-	/*
-	 * If there was no rseq previously registered, ensure the provided rseq
-	 * is properly aligned, as communcated to user-space through the ELF
-	 * auxiliary vector AT_RSEQ_ALIGN. If rseq_len is the original rseq
-	 * size, the required alignment is the original struct rseq alignment.
-	 *
-	 * The rseq_len is required to be greater or equal to the original rseq
-	 * size. In order to be valid, rseq_len is either the original rseq size,
-	 * or large enough to contain all supported fields, as communicated to
-	 * user-space through the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE.
-	 */
-	if (rseq_len < ORIG_RSEQ_SIZE ||
-	    (rseq_len == ORIG_RSEQ_SIZE && !IS_ALIGNED((unsigned long)rseq, ORIG_RSEQ_SIZE)) ||
-	    (rseq_len != ORIG_RSEQ_SIZE && (!IS_ALIGNED((unsigned long)rseq, rseq_alloc_align()) ||
-					    rseq_len < offsetof(struct rseq, end))))
-		return -EINVAL;
 	if (!access_ok(rseq, rseq_len))
 		return -EFAULT;
 
-	if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) {
-		rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;
-		if (rseq_slice_extension_enabled() &&
-		    (flags & RSEQ_FLAG_SLICE_EXT_DEFAULT_ON))
-			rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;
+	/*
+	 * Architectures, which use the generic IRQ entry code (at least) enable
+	 * registrations with a size greater than the original v1 fixed sized
+	 * @rseq_len, which has been validated already to utilize the optimized
+	 * v2 ABI mode which also enables extended RSEQ features beyond MMCID.
+	 */
+	if (IS_ENABLED(CONFIG_GENERIC_IRQ_ENTRY) && rseq_len > ORIG_RSEQ_SIZE)
+		version = 2;
+
+	if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION) && version > 1) {
+		if (rseq_slice_extension_enabled()) {
+			rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;
+			if (flags & RSEQ_FLAG_SLICE_EXT_DEFAULT_ON)
+				rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;
+		}
 	}
 
 	scoped_user_write_access(rseq, efault) {
@@ -485,7 +452,15 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
 		unsafe_put_user(RSEQ_CPU_ID_UNINITIALIZED, &rseq->cpu_id, efault);
 		unsafe_put_user(0U, &rseq->node_id, efault);
 		unsafe_put_user(0U, &rseq->mm_cid, efault);
-		unsafe_put_user(0U, &rseq->slice_ctrl.all, efault);
+
+		/*
+		 * All fields past mm_cid are only valid for non-legacy v2
+		 * registrations.
+		 */
+		if (version > 1) {
+			if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION))
+				unsafe_put_user(0U, &rseq->slice_ctrl.all, efault);
+		}
 	}
 
 	/*
@@ -501,11 +476,10 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
 #endif
 
 	/*
-	 * If rseq was previously inactive, and has just been
-	 * registered, ensure the cpu_id_start and cpu_id fields
-	 * are updated before returning to user-space.
+	 * Ensure the cpu_id_start and cpu_id fields are updated before
+	 * returning to user-space.
 	 */
-	current->rseq.event.has_rseq = true;
+	current->rseq.event.has_rseq = version;
 	rseq_force_update();
 	return 0;
 
@@ -513,6 +487,80 @@ efault:
 	return -EFAULT;
 }
 
+static long rseq_unregister(struct rseq __user * rseq, u32 rseq_len, int flags, u32 sig)
+{
+	if (flags & ~RSEQ_FLAG_UNREGISTER)
+		return -EINVAL;
+	if (current->rseq.usrptr != rseq || !current->rseq.usrptr)
+		return -EINVAL;
+	if (rseq_len != current->rseq.len)
+		return -EINVAL;
+	if (current->rseq.sig != sig)
+		return -EPERM;
+	if (!rseq_reset_ids())
+		return -EFAULT;
+	rseq_reset(current);
+	return 0;
+}
+
+static long rseq_reregister(struct rseq __user * rseq, u32 rseq_len, u32 sig)
+{
+	/*
+	 * If rseq is already registered, check whether the provided address
+	 * differs from the prior one.
+	 */
+	if (current->rseq.usrptr != rseq || rseq_len != current->rseq.len)
+		return -EINVAL;
+	if (current->rseq.sig != sig)
+		return -EPERM;
+	/* Already registered. */
+	return -EBUSY;
+}
+
+static bool rseq_length_valid(struct rseq __user *rseq, unsigned int rseq_len)
+{
+	/*
+	 * Ensure the provided rseq is properly aligned, as communicated to
+	 * user-space through the ELF auxiliary vector AT_RSEQ_ALIGN. If
+	 * rseq_len is the original rseq size, the required alignment is the
+	 * original struct rseq alignment.
+	 *
+	 * In order to be valid, rseq_len is either the original rseq size, or
+	 * large enough to contain all supported fields, as communicated to
+	 * user-space through the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE.
+	 */
+	if (rseq_len < ORIG_RSEQ_SIZE)
+		return false;
+
+	if (rseq_len == ORIG_RSEQ_SIZE)
+		return IS_ALIGNED((unsigned long)rseq, ORIG_RSEQ_SIZE);
+
+	return IS_ALIGNED((unsigned long)rseq, rseq_alloc_align()) &&
+		rseq_len >= offsetof(struct rseq, end);
+}
+
+#define RSEQ_FLAGS_SUPPORTED	(RSEQ_FLAG_SLICE_EXT_DEFAULT_ON)
+
+/*
+ * sys_rseq - Register or unregister restartable sequences for the caller thread.
+ */
+SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32, sig)
+{
+	if (flags & RSEQ_FLAG_UNREGISTER)
+		return rseq_unregister(rseq, rseq_len, flags, sig);
+
+	if (unlikely(flags & ~RSEQ_FLAGS_SUPPORTED))
+		return -EINVAL;
+
+	if (current->rseq.usrptr)
+		return rseq_reregister(rseq, rseq_len, sig);
+
+	if (!rseq_length_valid(rseq, rseq_len))
+		return -EINVAL;
+
+	return rseq_register(rseq, rseq_len, flags, sig);
+}
+
 #ifdef CONFIG_RSEQ_SLICE_EXTENSION
 struct slice_timer {
 	struct hrtimer	timer;
@@ -713,6 +761,8 @@ int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3)
 			return -ENOTSUPP;
 		if (!current->rseq.usrptr)
 			return -ENXIO;
+		if (!rseq_v2(current))
+			return -ENOTSUPP;
 
 		/* No change? */
 		if (enable == !!current->rseq.slice.state.enabled)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 728965851842..3ebec186f982 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -882,11 +882,11 @@ bool update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
  *
  * lag_i >= 0 -> V >= v_i
  *
- *     \Sum (v_i - v)*w_i
- * V = ------------------ + v
+ *     \Sum (v_i - v0)*w_i
+ * V = ------------------- + v0
  *          \Sum w_i
  *
- * lag_i >= 0 -> \Sum (v_i - v)*w_i >= (v_i - v)*(\Sum w_i)
+ * lag_i >= 0 -> \Sum (v_i - v0)*w_i >= (v_i - v0)*(\Sum w_i)
  *
  * Note: using 'avg_vruntime() > se->vruntime' is inaccurate due
  *       to the loss in precision caused by the division.
@@ -894,7 +894,7 @@ bool update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static int vruntime_eligible(struct cfs_rq *cfs_rq, u64 vruntime)
 {
 	struct sched_entity *curr = cfs_rq->curr;
-	s64 avg = cfs_rq->sum_w_vruntime;
+	s64 key, avg = cfs_rq->sum_w_vruntime;
 	long load = cfs_rq->sum_weight;
 
 	if (curr && curr->on_rq) {
@@ -904,7 +904,36 @@ static int vruntime_eligible(struct cfs_rq *cfs_rq, u64 vruntime)
 		load += weight;
 	}
 
-	return avg >= vruntime_op(vruntime, "-", cfs_rq->zero_vruntime) * load;
+	key = vruntime_op(vruntime, "-", cfs_rq->zero_vruntime);
+
+	/*
+	 * The worst case term for @key includes 'NSEC_TICK * NICE_0_LOAD'
+	 * and @load obviously includes NICE_0_LOAD. NSEC_TICK is around 24
+	 * bits, while NICE_0_LOAD is 20 on 64bit and 10 otherwise.
+	 *
+	 * This gives that on 64bit the product will be at least 64bit which
+	 * overflows s64, while on 32bit it will only be 44bits and should fit
+	 * comfortably.
+	 */
+#ifdef CONFIG_64BIT
+#ifdef CONFIG_ARCH_SUPPORTS_INT128
+	/* This often results in simpler code than __builtin_mul_overflow(). */
+	return avg >= (__int128)key * load;
+#else
+	s64 rhs;
+	/*
+	 * On overflow, the sign of key tells us the correct answer: a large
+	 * positive key means vruntime >> V, so not eligible; a large negative
+	 * key means vruntime << V, so eligible.
+	 */
+	if (check_mul_overflow(key, load, &rhs))
+		return key <= 0;
+
+	return avg >= rhs;
+#endif
+#else /* 32bit */
+	return avg >= key * load;
+#endif
 }
 
 int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -9145,9 +9174,10 @@ pick:
 
 	/*
 	 * Because p is enqueued, nse being null can only mean that we
-	 * dequeued a delayed task.
+	 * dequeued a delayed task. If there are still entities queued in
+	 * cfs, check if the next one will be p.
 	 */
-	if (!nse)
+	if (!nse && cfs_rq->nr_queued)
 		goto pick;
 
 	if (sched_feat(RUN_TO_PARITY))
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 623445603725..226a6329f3e9 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -199,7 +199,16 @@ static void ipi_rseq(void *info)
 	 * is negligible.
 	 */
 	smp_mb();
-	rseq_sched_switch_event(current);
+	/*
+	 * Legacy mode requires that IDs are written and the critical section is
+	 * evaluated. V2 optimized mode handles the critical section and IDs are
+	 * only updated if they change as a consequence of preemption after
+	 * return from this IPI.
+	 */
+	if (rseq_v2(current))
+		rseq_sched_switch_event(current);
+	else
+		rseq_force_update();
 }
 
 static void ipi_sync_rq_state(void *info)
diff --git a/tools/testing/selftests/rseq/Makefile b/tools/testing/selftests/rseq/Makefile
index 4ef90823b652..50d69e22ee7a 100644
--- a/tools/testing/selftests/rseq/Makefile
+++ b/tools/testing/selftests/rseq/Makefile
@@ -14,14 +14,20 @@ LDLIBS += -lpthread -ldl
 # still track changes to header files and depend on shared object.
 OVERRIDE_TARGETS = 1
 
-TEST_GEN_PROGS = basic_test basic_percpu_ops_test basic_percpu_ops_mm_cid_test param_test \
-		param_test_benchmark param_test_compare_twice param_test_mm_cid \
-		param_test_mm_cid_benchmark param_test_mm_cid_compare_twice \
-		syscall_errors_test slice_test
+TEST_GEN_PROGS = basic_test basic_percpu_ops_test basic_percpu_ops_mm_cid_test \
+		 param_test_benchmark param_test_mm_cid_benchmark
 
-TEST_GEN_PROGS_EXTENDED = librseq.so
+TEST_GEN_PROGS_EXTENDED = librseq.so \
+	param_test \
+	param_test_compare_twice \
+	param_test_mm_cid \
+	param_test_mm_cid_compare_twice \
+	syscall_errors_test \
+	legacy_check \
+	slice_test \
+	check_optimized
 
-TEST_PROGS = run_param_test.sh run_syscall_errors_test.sh
+TEST_PROGS = run_param_test.sh run_syscall_errors_test.sh run_legacy_check.sh run_timeslice_test.sh
 
 TEST_FILES := settings
 
@@ -62,3 +68,6 @@ $(OUTPUT)/syscall_errors_test: syscall_errors_test.c $(TEST_GEN_PROGS_EXTENDED)
 
 $(OUTPUT)/slice_test: slice_test.c $(TEST_GEN_PROGS_EXTENDED) rseq.h rseq-*.h
 	$(CC) $(CFLAGS) $< $(LDLIBS) -lrseq -o $@
+
+$(OUTPUT)/check_optimized: check_optimized.c $(TEST_GEN_PROGS_EXTENDED) rseq.h rseq-*.h
+	$(CC) $(CFLAGS) $< $(LDLIBS) -lrseq -o $@
diff --git a/tools/testing/selftests/rseq/check_optimized.c b/tools/testing/selftests/rseq/check_optimized.c
new file mode 100644
index 000000000000..a13e3f2c8fc6
--- /dev/null
+++ b/tools/testing/selftests/rseq/check_optimized.c
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: LGPL-2.1
+#define _GNU_SOURCE
+#include <assert.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/time.h>
+
+#include "rseq.h"
+
+int main(int argc, char **argv)
+{
+	if (__rseq_register_current_thread(true, false))
+		return -1;
+	return 0;
+}
diff --git a/tools/testing/selftests/rseq/legacy_check.c b/tools/testing/selftests/rseq/legacy_check.c
new file mode 100644
index 000000000000..3f7de4e28303
--- /dev/null
+++ b/tools/testing/selftests/rseq/legacy_check.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+#include <errno.h>
+#include <signal.h>
+#include <stdint.h>
+#include <unistd.h>
+
+#include "rseq.h"
+
+#include "../kselftest_harness.h"
+
+FIXTURE(legacy)
+{
+};
+
+static int cpu_id_in_sigfn = -1;
+
+static void sigfn(int sig)
+{
+	struct rseq_abi *rs = rseq_get_abi();
+
+	cpu_id_in_sigfn = rs->cpu_id_start;
+}
+
+FIXTURE_SETUP(legacy)
+{
+	int res = __rseq_register_current_thread(true, true);
+
+	switch (res) {
+	case -ENOSYS:
+		SKIP(return, "RSEQ not enabled\n");
+	case -EBUSY:
+		SKIP(return, "GLIBC owns RSEQ. Disable GLIBC RSEQ registration\n");
+	default:
+		ASSERT_EQ(res, 0);
+	}
+
+	ASSERT_NE(signal(SIGUSR1, sigfn), SIG_ERR);
+}
+
+FIXTURE_TEARDOWN(legacy)
+{
+}
+
+TEST_F(legacy, legacy_test)
+{
+	struct rseq_abi *rs = rseq_get_abi();
+
+	ASSERT_NE(rs, NULL);
+
+	/* Overwrite rs::cpu_id_start */
+	rs->cpu_id_start = -1;
+	sleep(1);
+	ASSERT_NE(rs->cpu_id_start, -1);
+
+	rs->cpu_id_start = -1;
+	ASSERT_EQ(raise(SIGUSR1), 0);
+	ASSERT_NE(rs->cpu_id_start, -1);
+	ASSERT_NE(cpu_id_in_sigfn, -1);
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/rseq/param_test.c b/tools/testing/selftests/rseq/param_test.c
index 05d03e679e06..e1e98dbabe4b 100644
--- a/tools/testing/selftests/rseq/param_test.c
+++ b/tools/testing/selftests/rseq/param_test.c
@@ -38,7 +38,7 @@ static int opt_modulo, verbose;
 static int opt_yield, opt_signal, opt_sleep,
 		opt_disable_rseq, opt_threads = 200,
 		opt_disable_mod = 0, opt_test = 's';
-
+static bool opt_rseq_legacy;
 static long long opt_reps = 5000;
 
 static __thread __attribute__((tls_model("initial-exec")))
@@ -281,9 +281,12 @@ unsigned int yield_mod_cnt, nr_abort;
 	} \
 }
 
+#define rseq_no_glibc			true
+
 #else
 
 #define printf_verbose(fmt, ...)
+#define rseq_no_glibc			false
 
 #endif /* BENCHMARK */
 
@@ -481,7 +484,7 @@ void *test_percpu_spinlock_thread(void *arg)
 	long long i, reps;
 
 	if (!opt_disable_rseq && thread_data->reg &&
-	    rseq_register_current_thread())
+	    __rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy))
 		abort();
 	reps = thread_data->reps;
 	for (i = 0; i < reps; i++) {
@@ -558,7 +561,7 @@ void *test_percpu_inc_thread(void *arg)
 	long long i, reps;
 
 	if (!opt_disable_rseq && thread_data->reg &&
-	    rseq_register_current_thread())
+	    __rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy))
 		abort();
 	reps = thread_data->reps;
 	for (i = 0; i < reps; i++) {
@@ -712,7 +715,7 @@ void *test_percpu_list_thread(void *arg)
 	long long i, reps;
 	struct percpu_list *list = (struct percpu_list *)arg;
 
-	if (!opt_disable_rseq && rseq_register_current_thread())
+	if (!opt_disable_rseq && __rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy))
 		abort();
 
 	reps = opt_reps;
@@ -895,7 +898,7 @@ void *test_percpu_buffer_thread(void *arg)
 	long long i, reps;
 	struct percpu_buffer *buffer = (struct percpu_buffer *)arg;
 
-	if (!opt_disable_rseq && rseq_register_current_thread())
+	if (!opt_disable_rseq && __rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy))
 		abort();
 
 	reps = opt_reps;
@@ -1105,7 +1108,7 @@ void *test_percpu_memcpy_buffer_thread(void *arg)
 	long long i, reps;
 	struct percpu_memcpy_buffer *buffer = (struct percpu_memcpy_buffer *)arg;
 
-	if (!opt_disable_rseq && rseq_register_current_thread())
+	if (!opt_disable_rseq && __rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy))
 		abort();
 
 	reps = opt_reps;
@@ -1258,7 +1261,7 @@ void *test_membarrier_worker_thread(void *arg)
 	const int iters = opt_reps;
 	int i;
 
-	if (rseq_register_current_thread()) {
+	if (__rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy)) {
 		fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
 			errno, strerror(errno));
 		abort();
@@ -1323,7 +1326,7 @@ void *test_membarrier_manager_thread(void *arg)
 	intptr_t expect_a = 0, expect_b = 0;
 	int cpu_a = 0, cpu_b = 0;
 
-	if (rseq_register_current_thread()) {
+	if (__rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy)) {
 		fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
 			errno, strerror(errno));
 		abort();
@@ -1475,6 +1478,7 @@ static void show_usage(int argc, char **argv)
 	printf("	[-D M] Disable rseq for each M threads\n");
 	printf("	[-T test] Choose test: (s)pinlock, (l)ist, (b)uffer, (m)emcpy, (i)ncrement, membarrie(r)\n");
 	printf("	[-M] Push into buffer and memcpy buffer with memory barriers.\n");
+	printf("	[-O] Test with optimized RSEQ\n");
 	printf("	[-v] Verbose output.\n");
 	printf("	[-h] Show this help.\n");
 	printf("\n");
@@ -1602,6 +1606,9 @@ int main(int argc, char **argv)
 		case 'M':
 			opt_mo = RSEQ_MO_RELEASE;
 			break;
+		case 'L':
+			opt_rseq_legacy = true;
+			break;
 		default:
 			show_usage(argc, argv);
 			goto error;
@@ -1618,7 +1625,7 @@ int main(int argc, char **argv)
 	if (set_signal_handler())
 		goto error;
 
-	if (!opt_disable_rseq && rseq_register_current_thread())
+	if (!opt_disable_rseq && __rseq_register_current_thread(rseq_no_glibc, opt_rseq_legacy))
 		goto error;
 	if (!opt_disable_rseq && !rseq_validate_cpu_id()) {
 		fprintf(stderr, "Error: cpu id getter unavailable\n");
diff --git a/tools/testing/selftests/rseq/rseq-abi.h b/tools/testing/selftests/rseq/rseq-abi.h
index ecef315204b2..5f4ea2152c2f 100644
--- a/tools/testing/selftests/rseq/rseq-abi.h
+++ b/tools/testing/selftests/rseq/rseq-abi.h
@@ -192,9 +192,14 @@ struct rseq_abi {
 	struct rseq_abi_slice_ctrl slice_ctrl;
 
 	/*
+	 * Place holder to push the size above 32 bytes.
+	 */
+	__u8 __reserved;
+
+	/*
 	 * Flexible array member at end of structure, after last feature field.
 	 */
 	char end[];
-} __attribute__((aligned(4 * sizeof(__u64))));
+} __attribute__((aligned(256)));
 
 #endif /* _RSEQ_ABI_H */
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index a736727b83c1..be0d0a97031e 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -56,6 +56,7 @@ ptrdiff_t rseq_offset;
  * unsuccessful.
  */
 unsigned int rseq_size = -1U;
+static unsigned int rseq_alloc_size;
 
 /* Flags used during rseq registration.  */
 unsigned int rseq_flags;
@@ -115,29 +116,17 @@ bool rseq_available(void)
 	}
 }
 
-/* The rseq areas need to be at least 32 bytes. */
-static
-unsigned int get_rseq_min_alloc_size(void)
-{
-	unsigned int alloc_size = rseq_size;
-
-	if (alloc_size < ORIG_RSEQ_ALLOC_SIZE)
-		alloc_size = ORIG_RSEQ_ALLOC_SIZE;
-	return alloc_size;
-}
-
 /*
  * Return the feature size supported by the kernel.
  *
  * Depending on the value returned by getauxval(AT_RSEQ_FEATURE_SIZE):
  *
- * 0:   Return ORIG_RSEQ_FEATURE_SIZE (20)
+ *   0: Return ORIG_RSEQ_FEATURE_SIZE (20)
  * > 0: Return the value from getauxval(AT_RSEQ_FEATURE_SIZE).
  *
  * It should never return a value below ORIG_RSEQ_FEATURE_SIZE.
  */
-static
-unsigned int get_rseq_kernel_feature_size(void)
+static unsigned int get_rseq_kernel_feature_size(void)
 {
 	unsigned long auxv_rseq_feature_size, auxv_rseq_align;
 
@@ -152,15 +141,24 @@ unsigned int get_rseq_kernel_feature_size(void)
 		return ORIG_RSEQ_FEATURE_SIZE;
 }
 
-int rseq_register_current_thread(void)
+int __rseq_register_current_thread(bool nolibc, bool legacy)
 {
+	unsigned int size;
 	int rc;
 
 	if (!rseq_ownership) {
 		/* Treat libc's ownership as a successful registration. */
-		return 0;
+		return nolibc ? -EBUSY : 0;
 	}
-	rc = sys_rseq(&__rseq.abi, get_rseq_min_alloc_size(), 0, RSEQ_SIG);
+
+	/* The minimal allocation size is 32, which is the legacy allocation size */
+	size = get_rseq_kernel_feature_size();
+	if (legacy || size < ORIG_RSEQ_ALLOC_SIZE)
+		rseq_alloc_size = ORIG_RSEQ_ALLOC_SIZE;
+	else
+		rseq_alloc_size = size;
+
+	rc = sys_rseq(&__rseq.abi, rseq_alloc_size, 0, RSEQ_SIG);
 	if (rc) {
 		/*
 		 * After at least one thread has registered successfully
@@ -179,9 +177,8 @@ int rseq_register_current_thread(void)
 	 * The first thread to register sets the rseq_size to mimic the libc
 	 * behavior.
 	 */
-	if (RSEQ_READ_ONCE(rseq_size) == 0) {
-		RSEQ_WRITE_ONCE(rseq_size, get_rseq_kernel_feature_size());
-	}
+	if (RSEQ_READ_ONCE(rseq_size) == 0)
+		RSEQ_WRITE_ONCE(rseq_size, size);
 
 	return 0;
 }
@@ -194,7 +191,7 @@ int rseq_unregister_current_thread(void)
 		/* Treat libc's ownership as a successful unregistration. */
 		return 0;
 	}
-	rc = sys_rseq(&__rseq.abi, get_rseq_min_alloc_size(), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
+	rc = sys_rseq(&__rseq.abi, rseq_alloc_size, RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
 	if (rc)
 		return -1;
 	return 0;
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index f51a5fdb0444..c62ebb9290c0 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -8,6 +8,7 @@
 #ifndef RSEQ_H
 #define RSEQ_H
 
+#include <assert.h>
 #include <stdint.h>
 #include <stdbool.h>
 #include <pthread.h>
@@ -142,7 +143,12 @@ static inline struct rseq_abi *rseq_get_abi(void)
  * succeed. A restartable sequence executed from a non-registered
  * thread will always fail.
  */
-int rseq_register_current_thread(void);
+int __rseq_register_current_thread(bool nolibc, bool legacy);
+
+static inline int rseq_register_current_thread(void)
+{
+	return __rseq_register_current_thread(false, false);
+}
 
 /*
  * Unregister rseq for current thread.
diff --git a/tools/testing/selftests/rseq/run_legacy_check.sh b/tools/testing/selftests/rseq/run_legacy_check.sh
new file mode 100755
index 000000000000..5577b46ea092
--- /dev/null
+++ b/tools/testing/selftests/rseq/run_legacy_check.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+GLIBC_TUNABLES="${GLIBC_TUNABLES:-}:glibc.pthread.rseq=0" ./legacy_check
diff --git a/tools/testing/selftests/rseq/run_param_test.sh b/tools/testing/selftests/rseq/run_param_test.sh
index 8d31426ab41f..69a3fa049929 100755
--- a/tools/testing/selftests/rseq/run_param_test.sh
+++ b/tools/testing/selftests/rseq/run_param_test.sh
@@ -34,6 +34,11 @@ REPS=1000
 SLOW_REPS=100
 NR_THREADS=$((6*${NR_CPUS}))
 
+# Prevent GLIBC from registering RSEQ so the selftest can run in legacy and
+# performance optimized mode.
+GLIBC_TUNABLES="${GLIBC_TUNABLES:-}:glibc.pthread.rseq=0"
+export GLIBC_TUNABLES
+
 function do_tests()
 {
 	local i=0
@@ -103,6 +108,40 @@ function inject_blocking()
 	NR_LOOPS=
 }
 
+echo "Testing in legacy RSEQ mode"
+echo "Yield injection (25%)"
+inject_blocking -m 4 -y -L
+
+echo "Yield injection (50%)"
+inject_blocking -m 2 -y -L
+
+echo "Yield injection (100%)"
+inject_blocking -m 1 -y -L
+
+echo "Kill injection (25%)"
+inject_blocking -m 4 -k -L
+
+echo "Kill injection (50%)"
+inject_blocking -m 2 -k -L
+
+echo "Kill injection (100%)"
+inject_blocking -m 1 -k -L
+
+echo "Sleep injection (1ms, 25%)"
+inject_blocking -m 4 -s 1 -L
+
+echo "Sleep injection (1ms, 50%)"
+inject_blocking -m 2 -s 1 -L
+
+echo "Sleep injection (1ms, 100%)"
+inject_blocking -m 1 -s 1 -L
+
+./check_optimized || {
+    echo "Skipping optimized RSEQ mode test. Not supported";
+    exit 0
+}
+
+echo "Testing in optimized RSEQ mode"
 echo "Yield injection (25%)"
 inject_blocking -m 4 -y
 
diff --git a/tools/testing/selftests/rseq/run_timeslice_test.sh b/tools/testing/selftests/rseq/run_timeslice_test.sh
new file mode 100755
index 000000000000..551ebed71ec6
--- /dev/null
+++ b/tools/testing/selftests/rseq/run_timeslice_test.sh
@@ -0,0 +1,14 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+
+# Prevent GLIBC from registering RSEQ so the selftest can run in legacy
+# and performance optimized mode.
+GLIBC_TUNABLES="${GLIBC_TUNABLES:-}:glibc.pthread.rseq=0"
+export GLIBC_TUNABLES
+
+./check_optimized || {
+    echo "Skipping optimized RSEQ mode test. Not supported";
+    exit 0
+}
+
+./slice_test
diff --git a/tools/testing/selftests/rseq/slice_test.c b/tools/testing/selftests/rseq/slice_test.c
index 357122dcb487..e402d4440bc2 100644
--- a/tools/testing/selftests/rseq/slice_test.c
+++ b/tools/testing/selftests/rseq/slice_test.c
@@ -124,6 +124,13 @@ FIXTURE_SETUP(slice_ext)
 {
 	cpu_set_t affinity;
 
+	if (__rseq_register_current_thread(true, false))
+		SKIP(return, "RSEQ not supported\n");
+
+	if (prctl(PR_RSEQ_SLICE_EXTENSION, PR_RSEQ_SLICE_EXTENSION_SET,
+		  PR_RSEQ_SLICE_EXT_ENABLE, 0, 0))
+		SKIP(return, "Time slice extension not supported\n");
+
 	ASSERT_EQ(sched_getaffinity(0, sizeof(affinity), &affinity), 0);
 
 	/* Pin it on a single CPU. Avoid CPU 0 */
@@ -137,11 +144,6 @@ FIXTURE_SETUP(slice_ext)
 		break;
 	}
 
-	ASSERT_EQ(rseq_register_current_thread(), 0);
-
-	ASSERT_EQ(prctl(PR_RSEQ_SLICE_EXTENSION, PR_RSEQ_SLICE_EXTENSION_SET,
-			PR_RSEQ_SLICE_EXT_ENABLE, 0, 0), 0);
-
 	self->noise_params.noise_nsecs = variant->noise_nsecs;
 	self->noise_params.sleep_nsecs = variant->sleep_nsecs;
 	self->noise_params.run = 1;