[RFC PATCH for 4.15 24/24] membarrier: arm64: Provide core serializing command

[Mathieu Desnoyers]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxx>
CC: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CC: Boqun Feng <boqun.feng@xxxxxxxxx>
CC: Andrew Hunter <ahh@xxxxxxxxxx>
CC: Maged Michael <maged.michael@xxxxxxxxx>
CC: Avi Kivity <avi@xxxxxxxxxxxx>
CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
CC: Paul Mackerras <paulus@xxxxxxxxx>
CC: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
CC: Dave Watson <davejwatson@xxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: Andrea Parri <parri.andrea@xxxxxxxxx>
CC: Russell King <linux@xxxxxxxxxxxxxxx>
CC: Greg Hackmann <ghackmann@xxxxxxxxxx>
CC: Will Deacon <will.deacon@xxxxxxx>
CC: David Sehr <sehr@xxxxxxxxxx>
CC: x86@xxxxxxxxxx
CC: linux-arch@xxxxxxxxxxxxxxx
---
 arch/arm64/Kconfig        | 1 +
 arch/arm64/kernel/entry.S | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0df64a6a56d4..38272601850d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -16,6 +16,7 @@ config ARM64
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
 	select ARCH_HAS_KCOV
+	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_SET_MEMORY
 	select ARCH_HAS_SG_CHAIN
 	select ARCH_HAS_STRICT_KERNEL_RWX
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index e1c59d4008a8..0ec02508e53c 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -300,6 +300,10 @@ alternative_else_nop_endif
 	ldp	x28, x29, [sp, #16 * 14]
 	ldr	lr, [sp, #S_LR]
 	add	sp, sp, #S_FRAME_SIZE		// restore sp
+	/*
+	 * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on eret context synchronization
+	 * when returning from IPI handler, and when returning to user-space.
+	 */
 	eret					// return to kernel
 	.endm
 
-- 
2.11.0