[PATCH v3 rcu 06/11] arch/arm64: Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option

[Paul E. McKenney]

The arm64 architecture uses either an LL/SC loop (old systems) or an LSE
stadd instruction (new systems) to implement this_cpu_add(), both of which
are NMI safe.  This means that the old and more-efficient srcu_read_lock()
may be used in NMI context, without the need for srcu_read_lock_nmisafe().
Therefore, add the new Kconfig option ARCH_HAS_NMI_SAFE_THIS_CPU_OPS to
arch/arm64/Kconfig, which will cause NEED_SRCU_NMI_SAFE to be deselected,
thus preserving the current srcu_read_lock() behavior.

Link: https://lore.kernel.org/all/20220910221947.171557773@xxxxxxxxxxxxx/

Suggested-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
Suggested-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Suggested-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: John Ogness <john.ogness@xxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 505c8a1ccbe0c..099ee812f3f18 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -31,6 +31,7 @@ config ARM64
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_KEEPINITRD
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
+	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PTE_DEVMAP
 	select ARCH_HAS_PTE_SPECIAL
-- 
2.31.1.189.g2e36527f23