[PATCH v4 3/4] locking: Introduce prepare_sync_core_cmd()

[Andrea Parri <parri.andrea@gmail.com>]

Introduce an architecture function that architectures can use to set
up ("prepare") SYNC_CORE commands.

The function will be used by RISC-V to update its "deferred icache-
flush" data structures (icache_stale_mask).

Architectures defining prepare_sync_core_cmd() static inline need to
select ARCH_HAS_PREPARE_SYNC_CORE_CMD.

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 include/linux/sync_core.h | 16 +++++++++++++++-
 init/Kconfig              |  3 +++
 kernel/sched/membarrier.c |  1 +
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/include/linux/sync_core.h b/include/linux/sync_core.h
index 013da4b8b3272..67bb9794b8758 100644
--- a/include/linux/sync_core.h
+++ b/include/linux/sync_core.h
@@ -17,5 +17,19 @@ static inline void sync_core_before_usermode(void)
 }
 #endif
 
-#endif /* _LINUX_SYNC_CORE_H */
+#ifdef CONFIG_ARCH_HAS_PREPARE_SYNC_CORE_CMD
+#include <asm/sync_core.h>
+#else
+/*
+ * This is a dummy prepare_sync_core_cmd() implementation that can be used on
+ * all architectures which provide unconditional core serializing instructions
+ * in switch_mm().
+ * If your architecture doesn't provide such core serializing instructions in
+ * switch_mm(), you may need to write your own functions.
+ */
+static inline void prepare_sync_core_cmd(struct mm_struct *mm)
+{
+}
+#endif
 
+#endif /* _LINUX_SYNC_CORE_H */
diff --git a/init/Kconfig b/init/Kconfig
index 8d4e836e1b6b1..e2bad47922642 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1982,6 +1982,9 @@ source "kernel/Kconfig.locks"
 config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	bool
 
+config ARCH_HAS_PREPARE_SYNC_CORE_CMD
+	bool
+
 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
 	bool
 
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index f3d91628d6b8a..6d1f31b3a967b 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -320,6 +320,7 @@ static int membarrier_private_expedited(int flags, int cpu_id)
 		      MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
 			return -EPERM;
 		ipi_func = ipi_sync_core;
+		prepare_sync_core_cmd(mm);
 	} else if (flags == MEMBARRIER_FLAG_RSEQ) {
 		if (!IS_ENABLED(CONFIG_RSEQ))
 			return -EINVAL;
-- 
2.34.1