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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 55DEEC5CFEB for ; Wed, 11 Jul 2018 18:39:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0179220C0E for ; Wed, 11 Jul 2018 18:39:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0179220C0E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=de.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 S2387401AbeGKSpT (ORCPT ); Wed, 11 Jul 2018 14:45:19 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48696 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726429AbeGKSpS (ORCPT ); Wed, 11 Jul 2018 14:45:18 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w6BId1sW074493 for ; Wed, 11 Jul 2018 14:39:42 -0400 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0b-001b2d01.pphosted.com with ESMTP id 2k5nu5krk6-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 11 Jul 2018 14:39:42 -0400 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 11 Jul 2018 19:39:37 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w6BIdbCD37093562 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 11 Jul 2018 18:39:37 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AC011A405E; Wed, 11 Jul 2018 21:39:58 +0100 (BST) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5E924A4055; Wed, 11 Jul 2018 21:39:58 +0100 (BST) Received: from oc7330422307.ibm.com (unknown [9.145.165.185]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 11 Jul 2018 21:39:58 +0100 (BST) Subject: Re: [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode To: paulmck@linux.vnet.ibm.com, David Woodhouse Cc: peterz@infradead.org, mhillenb@amazon.de, linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <20180711174843.GX3593@linux.vnet.ibm.com> <20180711180101.3711464-1-dwmw2@infradead.org> <20180711182053.GA3593@linux.vnet.ibm.com> <20180711183645.GA23820@linux.vnet.ibm.com> From: Christian Borntraeger Openpgp: preference=signencrypt Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180711183645.GA23820@linux.vnet.ibm.com> Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 18071118-0020-0000-0000-000002A57B01 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18071118-0021-0000-0000-000020F1C314 Message-Id: <62e945ee-a58e-f9b3-279c-74cd0f5809da@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-07-11_05:,, 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-1807110197 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/11/2018 08:36 PM, Paul E. McKenney wrote: > 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(); As indicated in my other mail. This is supposed to be handled in the guest_enter|exit_ calls around the run function. This would also handle other architectures. So if the guest_enter_irqoff code is not good enough, we should rather fix that instead of adding another rcu hint.