sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

2 files changed, 78 insertions, 0 deletions

diff --git a/include/uapi/misc/uacce/hisi_qm.h b/include/uapi/misc/uacce/hisi_qm.h
new file mode 100644
index 000000000..10504b48e
--- /dev/null
+++ b/include/uapi/misc/uacce/hisi_qm.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+#ifndef _UAPI_HISI_QM_H
+#define _UAPI_HISI_QM_H
+
+#include <linux/types.h>
+
+/**
+ * struct hisi_qp_ctx - User data for hisi qp.
+ * @id: qp_index return to user space
+ * @qc_type: Accelerator algorithm type
+ */
+struct hisi_qp_ctx {
+	__u16 id;
+	__u16 qc_type;
+};
+
+/**
+ * struct hisi_qp_info - User data for hisi qp.
+ * @sqe_size: Submission queue element size
+ * @sq_depth: The number of sqe
+ * @cq_depth: The number of cqe
+ * @reserved: Reserved data
+ */
+struct hisi_qp_info {
+	__u32 sqe_size;
+	__u16 sq_depth;
+	__u16 cq_depth;
+	__u64 reserved;
+};
+
+#define HISI_QM_API_VER_BASE "hisi_qm_v1"
+#define HISI_QM_API_VER2_BASE "hisi_qm_v2"
+#define HISI_QM_API_VER3_BASE "hisi_qm_v3"
+#define HISI_QM_API_VER5_BASE "hisi_qm_v5"
+
+/* UACCE_CMD_QM_SET_QP_CTX: Set qp algorithm type */
+#define UACCE_CMD_QM_SET_QP_CTX	_IOWR('H', 10, struct hisi_qp_ctx)
+/* UACCE_CMD_QM_SET_QP_INFO: Set qp depth and BD size */
+#define UACCE_CMD_QM_SET_QP_INFO _IOWR('H', 11, struct hisi_qp_info)
+#endif
diff --git a/include/uapi/misc/uacce/uacce.h b/include/uapi/misc/uacce/uacce.h
new file mode 100644
index 000000000..cc7185678
--- /dev/null
+++ b/include/uapi/misc/uacce/uacce.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+#ifndef _UAPIUUACCE_H
+#define _UAPIUUACCE_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+/*
+ * UACCE_CMD_START_Q: Start queue
+ */
+#define UACCE_CMD_START_Q	_IO('W', 0)
+
+/*
+ * UACCE_CMD_PUT_Q:
+ * User actively stop queue and free queue resource immediately
+ * Optimization method since close fd may delay
+ */
+#define UACCE_CMD_PUT_Q		_IO('W', 1)
+
+/*
+ * UACCE Device flags:
+ * UACCE_DEV_SVA: Shared Virtual Addresses
+ *		  Support PASID
+ *		  Support device page faults (PCI PRI or SMMU Stall)
+ */
+#define UACCE_DEV_SVA		BIT(0)
+
+/**
+ * enum uacce_qfrt: queue file region type
+ * @UACCE_QFRT_MMIO: device mmio region
+ * @UACCE_QFRT_DUS: device user share region
+ */
+enum uacce_qfrt {
+	UACCE_QFRT_MMIO = 0,
+	UACCE_QFRT_DUS = 1,
+};
+
+#endif