linux-kernel - [PATCH RFC v2 rcu 8/8] arch/s390: Add ARCH_HAS_NMI_SAFE_THIS_CPU

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Date:   Thu, 29 Sep 2022 11:07:31 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>, linux-s390@...r.kernel.org
Subject: [PATCH RFC v2 rcu 8/8] arch/s390: Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option

The s390 architecture uses either a cmpxchg loop (old systems)
or the laa add-to-memory 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@linutronix.de/

Suggested-by: Neeraj Upadhyay <quic_neeraju@...cinc.com>
Suggested-by: Frederic Weisbecker <frederic@...nel.org>
Suggested-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Heiko Carstens <hca@...ux.ibm.com>
Cc: Vasily Gorbik <gor@...ux.ibm.com>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
Cc: Sven Schnelle <svens@...ux.ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: John Ogness <john.ogness@...utronix.de>
Cc: Petr Mladek <pmladek@...e.com>
Cc: <linux-s390@...r.kernel.org>
---
 arch/s390/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 318fce77601d..0acdfda33290 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -73,6 +73,7 @@ config S390
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_MEM_ENCRYPT
+	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SCALED_CPUTIME
 	select ARCH_HAS_SET_MEMORY
-- 
2.31.1.189.g2e36527f23