linux-kernel - Re: [PATCH v3 rcu 08/11] arch/s390: Add ARCH_HAS_NMI_SAFE_THIS_CPU

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Date:   Thu, 20 Oct 2022 07:16:44 +0200
From:   Christian Borntraeger <borntraeger@...ux.ibm.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.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>,
        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: Re: [PATCH v3 rcu 08/11] arch/s390: Add
 ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option



Am 20.10.22 um 00:58 schrieb Paul E. McKenney:
> 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
						s390 ?
> 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 318fce77601d3..0acdfda332908 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