sched/umcg: add UMCG syscall stubs and CONFIG_UMCG

User Managed Concurrency Groups is a fast context switching and
in-process userspace scheduling framework.

Two main use cases are security sandboxes and userspace scheduling.

Security sandboxes: fast X-process context switching will open up a
bunch of light-weight security tools, e.g. gVisor, or Tor Project's
Shadow simulator, to more use cases.

In-process userspace scheduling is used extensively at Google to provide
latency control and isolation guarantees for diverse workloads while
maintaining high CPU utilization.

Signed-off-by: Peter Oskolkov <posk@google.com>

arch/x86/entry/syscalls/syscall_64.tbl

@@ -368,6 +368,17 @@
 444	common	landlock_create_ruleset	sys_landlock_create_ruleset
 445	common	landlock_add_rule	sys_landlock_add_rule
 446	common	landlock_restrict_self	sys_landlock_restrict_self
+447	common	umcg_api_version	sys_umcg_api_version
+448	common	umcg_register_task	sys_umcg_register_task
+449	common	umcg_unregister_task	sys_umcg_unregister_task
+450	common	umcg_wait		sys_umcg_wait
+451	common	umcg_wake		sys_umcg_wake
+452	common	umcg_swap		sys_umcg_swap
+453	common	umcg_create_group	sys_umcg_create_group
+454	common	umcg_destroy_group	sys_umcg_destroy_group
+455	common	umcg_poll_worker	sys_umcg_poll_worker
+456	common	umcg_run_worker		sys_umcg_run_worker
+457	common	umcg_preempt_worker	sys_umcg_preempt_worker
 
 #
 # Due to a historical design error, certain syscalls are numbered differently

include/uapi/asm-generic/unistd.h

@@ -873,8 +873,31 @@ __SYSCALL(__NR_landlock_add_rule, sys_landlock_add_rule)
 #define __NR_landlock_restrict_self 446
 __SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)
 
+#define __NR_umcg_api_version 447
+__SYSCALL(__NR_umcg_api_version, sys_umcg_api_version)
+#define __NR_umcg_register_task 448
+__SYSCALL(__NR_umcg_register_task, sys_umcg_register_task)
+#define __NR_umcg_unregister_task 449
+__SYSCALL(__NR_umcg_unregister_task, sys_umcg_unregister_task)
+#define __NR_umcg_wait 450
+__SYSCALL(__NR_umcg_wait, sys_umcg_wait)
+#define __NR_umcg_wake 451
+__SYSCALL(__NR_umcg_wake, sys_umcg_wake)
+#define __NR_umcg_swap 452
+__SYSCALL(__NR_umcg_swap, sys_umcg_swap)
+#define __NR_umcg_create_group 453
+__SYSCALL(__NR_umcg_create_group, sys_umcg_create_group)
+#define __NR_umcg_destroy_group 454
+__SYSCALL(__NR_umcg_destroy_group, sys_umcg_destroy_group)
+#define __NR_umcg_poll_worker 455
+__SYSCALL(__NR_umcg_poll_worker, sys_umcg_poll_worker)
+#define __NR_umcg_run_worker 456
+__SYSCALL(__NR_umcg_run_worker, sys_umcg_run_worker)
+#define __NR_umcg_preempt_worker 457
+__SYSCALL(__NR_umcg_preempt_worker, sys_umcg_preempt_worker)
+
 #undef __NR_syscalls
-#define __NR_syscalls 447
+#define __NR_syscalls 458
 
 /*
  * 32 bit systems traditionally used different

init/Kconfig

@@ -1661,6 +1661,16 @@ config MEMBARRIER
 
 	  If unsure, say Y.
 
+config UMCG
+	bool "Enable User Managed Concurrency Groups API"
+	default n
+	help
+	  Enable UMCG core wait/wake/swap operations as well as UMCG
+	  group/server/worker API. The core API is useful for fast IPC
+	  and context switching, while the group/server/worker API, together
+	  with the core API, form the basis for an in-process M:N userspace
+	  scheduling framework implemented in lib/umcg.
+
 config KALLSYMS
 	bool "Load all symbols for debugging/ksymoops" if EXPERT
 	default y

kernel/sys_ni.c

@@ -272,6 +272,19 @@ COND_SYSCALL(landlock_create_ruleset);
 COND_SYSCALL(landlock_add_rule);
 COND_SYSCALL(landlock_restrict_self);
 
+/* kernel/sched/umcg.c */
+COND_SYSCALL(umcg_api_version);
+COND_SYSCALL(umcg_register_task);
+COND_SYSCALL(umcg_unregister_task);
+COND_SYSCALL(umcg_wait);
+COND_SYSCALL(umcg_wake);
+COND_SYSCALL(umcg_swap);
+COND_SYSCALL(umcg_create_group);
+COND_SYSCALL(umcg_destroy_group);
+COND_SYSCALL(umcg_poll_worker);
+COND_SYSCALL(umcg_run_worker);
+COND_SYSCALL(umcg_preempt_worker);
+
 /* arch/example/kernel/sys_example.c */
 
 /* mm/fadvise.c */