From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5840DC5CFEB for ; Wed, 11 Jul 2018 18:34:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0931520C51 for ; Wed, 11 Jul 2018 18:34:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0931520C51 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.vnet.ibm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388514AbeGKSkH (ORCPT ); Wed, 11 Jul 2018 14:40:07 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:55722 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732957AbeGKSkG (ORCPT ); Wed, 11 Jul 2018 14:40:06 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w6BIUKOM027969 for ; Wed, 11 Jul 2018 14:34:32 -0400 Received: from e15.ny.us.ibm.com (e15.ny.us.ibm.com [129.33.205.205]) by mx0a-001b2d01.pphosted.com with ESMTP id 2k5md9fdjp-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 11 Jul 2018 14:34:32 -0400 Received: from localhost by e15.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 11 Jul 2018 14:34:30 -0400 Received: from b01cxnp22034.gho.pok.ibm.com (9.57.198.24) by e15.ny.us.ibm.com (146.89.104.202) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 11 Jul 2018 14:34:27 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w6BIYQBQ2425278 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 11 Jul 2018 18:34:26 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9081AB2064; Wed, 11 Jul 2018 14:34:25 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 60CEAB206A; Wed, 11 Jul 2018 14:34:25 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.159]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 11 Jul 2018 14:34:25 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 5BAF716C3B70; Wed, 11 Jul 2018 11:36:45 -0700 (PDT) Date: Wed, 11 Jul 2018 11:36:45 -0700 From: "Paul E. McKenney" To: David Woodhouse Cc: peterz@infradead.org, mhillenb@amazon.de, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode Reply-To: paulmck@linux.vnet.ibm.com References: <20180711174843.GX3593@linux.vnet.ibm.com> <20180711180101.3711464-1-dwmw2@infradead.org> <20180711182053.GA3593@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180711182053.GA3593@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18071118-0068-0000-0000-000003168FEB X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009352; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01059897; UDB=6.00544006; IPR=6.00837817; MB=3.00022105; MTD=3.00000008; XFM=3.00000015; UTC=2018-07-11 18:34:29 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18071118-0069-0000-0000-000044FECFC7 Message-Id: <20180711183645.GA23820@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-07-11_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1807110195 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 11, 2018 at 11:20:53AM -0700, Paul E. McKenney wrote: > On Wed, Jul 11, 2018 at 07:01:01PM +0100, David Woodhouse wrote: > > From: David Woodhouse > > > > RCU can spend long periods of time waiting for a CPU which is actually in > > KVM guest mode, entirely pointlessly. Treat it like the idle and userspace > > modes, and don't wait for it. > > > > Signed-off-by: David Woodhouse > > And idiot here forgot about some of the debugging code in RCU's dyntick-idle > code. I will reply with a fixed patch. > > The code below works just fine as long as you don't enable CONFIG_RCU_EQS_DEBUG, > so should be OK for testing, just not for mainline. And here is the updated code that allegedly avoids splatting when run with CONFIG_RCU_EQS_DEBUG. Thoughts? Thanx, Paul ------------------------------------------------------------------------ commit 12cd59e49cf734f907f44b696e2c6e4b46a291c3 Author: David Woodhouse Date: Wed Jul 11 19:01:01 2018 +0100 kvm/x86: Inform RCU of quiescent state when entering guest mode RCU can spend long periods of time waiting for a CPU which is actually in KVM guest mode, entirely pointlessly. Treat it like the idle and userspace modes, and don't wait for it. Signed-off-by: David Woodhouse Signed-off-by: Paul E. McKenney [ paulmck: Adjust to avoid bad advice I gave to dwmw, avoid WARN_ON()s. ] diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0046aa70205a..b0c82f70afa7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7458,7 +7458,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD; } + rcu_kvm_enter(); kvm_x86_ops->run(vcpu); + rcu_kvm_exit(); /* * Do this here before restoring debug registers on the host. And diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 7fa4fb9e899e..4b2d691e453f 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -85,6 +85,8 @@ static inline void rcu_virt_note_context_switch(int cpu) { } static inline void rcu_cpu_stall_reset(void) { } static inline void rcu_idle_enter(void) { } static inline void rcu_idle_exit(void) { } +static inline void rcu_kvm_enter(void) { } +static inline void rcu_kvm_exit(void) { } static inline void rcu_irq_enter(void) { } static inline void rcu_irq_exit_irqson(void) { } static inline void rcu_irq_enter_irqson(void) { } diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 7f83179177d1..48ce58b53ece 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -55,6 +55,8 @@ void cond_synchronize_rcu(unsigned long oldstate); void rcu_idle_enter(void); void rcu_idle_exit(void); +void rcu_kvm_enter(void); +void rcu_kvm_exit(void); void rcu_irq_enter(void); void rcu_irq_exit(void); void rcu_irq_enter_irqson(void); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 765c81dd675e..0c0672faa6d1 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -583,6 +583,24 @@ void rcu_idle_enter(void) rcu_eqs_enter(false); } +/** + * rcu_kvm_enter - inform RCU that current CPU is entering a guest OS + * + * Enter guest-OS mode, in other words, -leave- the mode in which RCU + * read-side critical sections can occur. (Though RCU read-side critical + * sections can occur in irq handlers from guest OSes, a possibility + * handled by irq_enter() and irq_exit().) + * + * If you add or remove a call to rcu_kvm_enter(), be sure to test with + * CONFIG_RCU_EQS_DEBUG=y. + */ +void rcu_kvm_enter(void) +{ + lockdep_assert_irqs_disabled(); + rcu_eqs_enter(true); +} +EXPORT_SYMBOL_GPL(rcu_kvm_enter); + #ifdef CONFIG_NO_HZ_FULL /** * rcu_user_enter - inform RCU that we are resuming userspace. @@ -747,6 +765,22 @@ void rcu_idle_exit(void) local_irq_restore(flags); } +/** + * rcu_kvm_exit - inform RCU that current CPU is leaving a guest OS + * + * Exit guest-OS mode, in other words, -enter- the mode in which RCU + * read-side critical sections can occur. + * + * If you add or remove a call to rcu_kvm_exit(), be sure to test with + * CONFIG_RCU_EQS_DEBUG=y. + */ +void rcu_kvm_exit(void) +{ + lockdep_assert_irqs_disabled(); + rcu_eqs_exit(true); +} +EXPORT_SYMBOL_GPL(rcu_kvm_exit); + #ifdef CONFIG_NO_HZ_FULL /** * rcu_user_exit - inform RCU that we are exiting userspace.