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/s390/Kconfig, which will
cause NEED_SRCU_NMI_SAFE to be deselected, thus preserving the current
srcu_read_lock() behavior.

[ paulmck: Apply Christian Borntraeger feedback. ]

Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/
Suggested-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Suggested-by: Frederic Weisbecker <frederic@kernel.org>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: <linux-s390@vger.kernel.org>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 318fce77601d357f84358c4200cd8492ef9513a7..0acdfda332908daa106ea1a3f978ad5a1525f679 100644 (file)
--- 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