rseq: Add fields and constants for time slice extension

Aside of a Kconfig knob add the following items:

   - Two flag bits for the rseq user space ABI, which allow user space to
     query the availability and enablement without a syscall.

   - A new member to the user space ABI struct rseq, which is going to be
     used to communicate request and grant between kernel and user space.

   - A rseq state struct to hold the kernel state of this

   - Documentation of the new mechanism

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251215155708.669472597@linutronix.de

1 files changed, 27 insertions, 1 deletions

diff --git a/include/linux/rseq_types.h b/include/linux/rseq_types.h
index 332dc14b81c9..67e40c059b1b 100644
--- a/include/linux/rseq_types.h
+++ b/include/linux/rseq_types.h
@@ -73,12 +73,35 @@ struct rseq_ids {
 };
 
 /**
+ * union rseq_slice_state - Status information for rseq time slice extension
+ * @state:	Compound to access the overall state
+ * @enabled:	Time slice extension is enabled for the task
+ * @granted:	Time slice extension was granted to the task
+ */
+union rseq_slice_state {
+	u16			state;
+	struct {
+		u8		enabled;
+		u8		granted;
+	};
+};
+
+/**
+ * struct rseq_slice - Status information for rseq time slice extension
+ * @state:	Time slice extension state
+ */
+struct rseq_slice {
+	union rseq_slice_state	state;
+};
+
+/**
  * struct rseq_data - Storage for all rseq related data
  * @usrptr:	Pointer to the registered user space RSEQ memory
  * @len:	Length of the RSEQ region
- * @sig:	Signature of critial section abort IPs
+ * @sig:	Signature of critical section abort IPs
  * @event:	Storage for event management
  * @ids:	Storage for cached CPU ID and MM CID
+ * @slice:	Storage for time slice extension data
  */
 struct rseq_data {
 	struct rseq __user		*usrptr;
@@ -86,6 +109,9 @@ struct rseq_data {
 	u32				sig;
 	struct rseq_event		event;
 	struct rseq_ids			ids;
+#ifdef CONFIG_RSEQ_SLICE_EXTENSION
+	struct rseq_slice		slice;
+#endif
 };
 
 #else /* CONFIG_RSEQ */