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>

10 files changed, 503 insertions, 0 deletions

diff --git a/arch/hexagon/include/uapi/asm/Kbuild b/arch/hexagon/include/uapi/asm/Kbuild
new file mode 100644
index 000000000..2501e82a1
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/Kbuild
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+syscall-y += unistd_32.h
+
+generic-y += ucontext.h
diff --git a/arch/hexagon/include/uapi/asm/byteorder.h b/arch/hexagon/include/uapi/asm/byteorder.h
new file mode 100644
index 000000000..1364fa4b2
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/byteorder.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#ifndef _ASM_BYTEORDER_H
+#define _ASM_BYTEORDER_H
+
+#if defined(__GNUC__) && !defined(__STRICT_ANSI__) || defined(__KERNEL__)
+#  define __BYTEORDER_HAS_U64__
+#endif
+
+#include <linux/byteorder/little_endian.h>
+
+#endif /* _ASM_BYTEORDER_H */
diff --git a/arch/hexagon/include/uapi/asm/param.h b/arch/hexagon/include/uapi/asm/param.h
new file mode 100644
index 000000000..a1283866d
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/param.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#ifndef _ASM_PARAM_H
+#define _ASM_PARAM_H
+
+#define EXEC_PAGESIZE	16384
+
+#include <asm-generic/param.h>
+
+#endif
diff --git a/arch/hexagon/include/uapi/asm/ptrace.h b/arch/hexagon/include/uapi/asm/ptrace.h
new file mode 100644
index 000000000..2a3ea14ad
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/ptrace.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Ptrace definitions for the Hexagon architecture
+ *
+ * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#ifndef _ASM_PTRACE_H
+#define _ASM_PTRACE_H
+
+#include <asm/registers.h>
+
+#define instruction_pointer(regs) pt_elr(regs)
+#define user_stack_pointer(regs) ((regs)->r29)
+
+#define profile_pc(regs) instruction_pointer(regs)
+
+#endif
diff --git a/arch/hexagon/include/uapi/asm/registers.h b/arch/hexagon/include/uapi/asm/registers.h
new file mode 100644
index 000000000..d51270f3b
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/registers.h
@@ -0,0 +1,229 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Register definitions for the Hexagon architecture
+ */
+
+
+#ifndef _ASM_REGISTERS_H
+#define _ASM_REGISTERS_H
+
+#ifndef __ASSEMBLY__
+
+/*  See kernel/entry.S for further documentation.  */
+
+/*
+ * Entry code copies the event record out of guest registers into
+ * this structure (which is on the stack).
+ */
+
+struct hvm_event_record {
+	unsigned long vmel;     /* Event Linkage (return address) */
+	unsigned long vmest;    /* Event context - pre-event SSR values */
+	unsigned long vmpsp;    /* Previous stack pointer */
+	unsigned long vmbadva;  /* Bad virtual address for addressing events */
+};
+
+struct pt_regs {
+	long restart_r0;        /* R0 checkpoint for syscall restart */
+	long syscall_nr;        /* Only used in system calls */
+	union {
+		struct {
+			unsigned long usr;
+			unsigned long preds;
+		};
+		long long int predsusr;
+	};
+	union {
+		struct {
+			unsigned long m0;
+			unsigned long m1;
+		};
+		long long int m1m0;
+	};
+	union {
+		struct {
+			unsigned long sa1;
+			unsigned long lc1;
+		};
+		long long int lc1sa1;
+	};
+	union {
+		struct {
+			unsigned long sa0;
+			unsigned long lc0;
+		};
+		long long int lc0sa0;
+	};
+	union {
+		struct {
+			unsigned long ugp;
+			unsigned long gp;
+		};
+		long long int gpugp;
+	};
+	union {
+		struct {
+			unsigned long cs0;
+			unsigned long cs1;
+		};
+		long long int cs1cs0;
+	};
+	/*
+	* Be extremely careful with rearranging these, if at all.  Some code
+	* assumes the 32 registers exist exactly like this in memory;
+	* e.g. kernel/ptrace.c
+	* e.g. kernel/signal.c (restore_sigcontext)
+	*/
+	union {
+		struct {
+			unsigned long r00;
+			unsigned long r01;
+		};
+		long long int r0100;
+	};
+	union {
+		struct {
+			unsigned long r02;
+			unsigned long r03;
+		};
+		long long int r0302;
+	};
+	union {
+		struct {
+			unsigned long r04;
+			unsigned long r05;
+		};
+		long long int r0504;
+	};
+	union {
+		struct {
+			unsigned long r06;
+			unsigned long r07;
+		};
+		long long int r0706;
+	};
+	union {
+		struct {
+			unsigned long r08;
+			unsigned long r09;
+		};
+		long long int r0908;
+	};
+	union {
+	       struct {
+			unsigned long r10;
+			unsigned long r11;
+	       };
+	       long long int r1110;
+	};
+	union {
+	       struct {
+			unsigned long r12;
+			unsigned long r13;
+	       };
+	       long long int r1312;
+	};
+	union {
+	       struct {
+			unsigned long r14;
+			unsigned long r15;
+	       };
+	       long long int r1514;
+	};
+	union {
+		struct {
+			unsigned long r16;
+			unsigned long r17;
+		};
+		long long int r1716;
+	};
+	union {
+		struct {
+			unsigned long r18;
+			unsigned long r19;
+		};
+		long long int r1918;
+	};
+	union {
+		struct {
+			unsigned long r20;
+			unsigned long r21;
+		};
+		long long int r2120;
+	};
+	union {
+		struct {
+			unsigned long r22;
+			unsigned long r23;
+		};
+		long long int r2322;
+	};
+	union {
+		struct {
+			unsigned long r24;
+			unsigned long r25;
+		};
+		long long int r2524;
+	};
+	union {
+		struct {
+			unsigned long r26;
+			unsigned long r27;
+		};
+		long long int r2726;
+	};
+	union {
+		struct {
+			unsigned long r28;
+			unsigned long r29;
+	       };
+	       long long int r2928;
+	};
+	union {
+		struct {
+			unsigned long r30;
+			unsigned long r31;
+		};
+		long long int r3130;
+	};
+	/* VM dispatch pushes event record onto stack - we can build on it */
+	struct hvm_event_record hvmer;
+};
+
+/* Defines to conveniently access the values  */
+
+/*
+ * As of the VM spec 0.5, these registers are now set/retrieved via a
+ * VM call.  On the in-bound side, we just fetch the values
+ * at the entry points and stuff them into the old record in pt_regs.
+ * However, on the outbound side, probably at VM rte, we set the
+ * registers back.
+ */
+
+#define pt_elr(regs) ((regs)->hvmer.vmel)
+#define pt_set_elr(regs, val) ((regs)->hvmer.vmel = (val))
+#define pt_cause(regs) ((regs)->hvmer.vmest & (HVM_VMEST_CAUSE_MSK))
+#define user_mode(regs) \
+	(((regs)->hvmer.vmest & (HVM_VMEST_UM_MSK << HVM_VMEST_UM_SFT)) != 0)
+#define ints_enabled(regs) \
+	(((regs)->hvmer.vmest & (HVM_VMEST_IE_MSK << HVM_VMEST_IE_SFT)) != 0)
+#define pt_psp(regs) ((regs)->hvmer.vmpsp)
+#define pt_badva(regs) ((regs)->hvmer.vmbadva)
+
+#define pt_set_singlestep(regs) ((regs)->hvmer.vmest |= (1<<HVM_VMEST_SS_SFT))
+#define pt_clr_singlestep(regs) ((regs)->hvmer.vmest &= ~(1<<HVM_VMEST_SS_SFT))
+
+#define pt_set_rte_sp(regs, sp) do {\
+	pt_psp(regs) = (regs)->r29 = (sp);\
+	} while (0)
+
+#define pt_set_kmode(regs) \
+	(regs)->hvmer.vmest = (HVM_VMEST_IE_MSK << HVM_VMEST_IE_SFT)
+
+#define pt_set_usermode(regs) \
+	(regs)->hvmer.vmest = (HVM_VMEST_UM_MSK << HVM_VMEST_UM_SFT) \
+			    | (HVM_VMEST_IE_MSK << HVM_VMEST_IE_SFT)
+
+#endif  /*  ifndef __ASSEMBLY  */
+
+#endif
diff --git a/arch/hexagon/include/uapi/asm/setup.h b/arch/hexagon/include/uapi/asm/setup.h
new file mode 100644
index 000000000..598f74f67
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/setup.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#ifndef _UAPI_ASM_HEXAGON_SETUP_H
+#define _UAPI_ASM_HEXAGON_SETUP_H
+
+#include <asm-generic/setup.h>
+
+#endif
diff --git a/arch/hexagon/include/uapi/asm/sigcontext.h b/arch/hexagon/include/uapi/asm/sigcontext.h
new file mode 100644
index 000000000..179a97041
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/sigcontext.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#ifndef _ASM_SIGCONTEXT_H
+#define _ASM_SIGCONTEXT_H
+
+#include <asm/user.h>
+
+/*
+ * Signal context structure - contains all info to do with the state
+ * before the signal handler was invoked.  Note: only add new entries
+ * to the end of the structure.
+ */
+struct sigcontext {
+	struct user_regs_struct sc_regs;
+} __attribute__((aligned(8)));
+
+#endif
diff --git a/arch/hexagon/include/uapi/asm/swab.h b/arch/hexagon/include/uapi/asm/swab.h
new file mode 100644
index 000000000..b39f12104
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/swab.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#ifndef _ASM_SWAB_H
+#define _ASM_SWAB_H
+
+#define __SWAB_64_THRU_32__
+
+#endif
diff --git a/arch/hexagon/include/uapi/asm/unistd.h b/arch/hexagon/include/uapi/asm/unistd.h
new file mode 100644
index 000000000..a3b0cac25
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/unistd.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Syscall support for Hexagon
+ *
+ * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+/*
+ *  The kernel pulls this unistd.h in three different ways:
+ *  1.  the "normal" way which gets all the __NR defines
+ *  2.  with __SYSCALL defined to produce function declarations
+ *  3.  with __SYSCALL defined to produce syscall table initialization
+ *  See also:  syscalltab.c
+ */
+
+#include <asm/unistd_32.h>
+
+#define __NR_sync_file_range2 84
+#undef __NR_sync_file_range
diff --git a/arch/hexagon/include/uapi/asm/user.h b/arch/hexagon/include/uapi/asm/user.h
new file mode 100644
index 000000000..abae6a4b5
--- /dev/null
+++ b/arch/hexagon/include/uapi/asm/user.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef HEXAGON_ASM_USER_H
+#define HEXAGON_ASM_USER_H
+
+/*
+ * Layout for registers passed in elf core dumps to userspace.
+ *
+ * Basically a rearranged subset of "pt_regs".
+ *
+ * Interested parties:  libc, gdb...
+ */
+
+struct user_regs_struct {
+	unsigned long r0;
+	unsigned long r1;
+	unsigned long r2;
+	unsigned long r3;
+	unsigned long r4;
+	unsigned long r5;
+	unsigned long r6;
+	unsigned long r7;
+	unsigned long r8;
+	unsigned long r9;
+	unsigned long r10;
+	unsigned long r11;
+	unsigned long r12;
+	unsigned long r13;
+	unsigned long r14;
+	unsigned long r15;
+	unsigned long r16;
+	unsigned long r17;
+	unsigned long r18;
+	unsigned long r19;
+	unsigned long r20;
+	unsigned long r21;
+	unsigned long r22;
+	unsigned long r23;
+	unsigned long r24;
+	unsigned long r25;
+	unsigned long r26;
+	unsigned long r27;
+	unsigned long r28;
+	unsigned long r29;
+	unsigned long r30;
+	unsigned long r31;
+	unsigned long sa0;
+	unsigned long lc0;
+	unsigned long sa1;
+	unsigned long lc1;
+	unsigned long m0;
+	unsigned long m1;
+	unsigned long usr;
+	unsigned long p3_0;
+	unsigned long gp;
+	unsigned long ugp;
+	unsigned long pc;
+	unsigned long cause;
+	unsigned long badva;
+	/* cs0 and cs1 are only available with HEXAGON_ARCH_VERSION >= 4 */
+	unsigned long cs0;
+	unsigned long cs1;
+	unsigned long pad1;  /* pad out to 48 words total */
+};
+
+#endif