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([2a0c:5a80:3511:9200:f938:102b:34c2:d5db]) by smtp.gmail.com with ESMTPSA id b10sm8204839wrg.19.2021.12.17.08.20.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Dec 2021 08:20:21 -0800 (PST) Message-ID: <27231550b5600072da918aa41c07404dea13590e.camel@redhat.com> Subject: Re: Possible nohz-full/RCU issue in arm64 KVM From: Nicolas Saenz Julienne To: paulmck@kernel.org, Paolo Bonzini Cc: Mark Rutland , maz , frederic , linux-kernel , rcu , Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel Date: Fri, 17 Dec 2021 17:20:21 +0100 In-Reply-To: <20211217160749.GS641268@paulmck-ThinkPad-P17-Gen-1> References: <70f112072d9496d21901946ea82832d3ed3a8cb2.camel@redhat.com> <9ab8107f-ff41-6a9e-57e1-a261bea93aca@redhat.com> <20211217160749.GS641268@paulmck-ThinkPad-P17-Gen-1> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.2 (3.42.2-1.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, On Fri, 2021-12-17 at 08:07 -0800, Paul E. McKenney wrote: > On Fri, Dec 17, 2021 at 04:54:22PM +0100, Paolo Bonzini wrote: > > On 12/17/21 15:38, Mark Rutland wrote: > > > For example kvm_guest_enter_irqoff() calls guest_enter_irq_off() which calls > > > vtime_account_guest_enter(), but kvm_guest_exit_irqoff() doesn't call > > > guest_exit_irq_off() and the call to vtime_account_guest_exit() is open-coded > > > elsewhere. Also, guest_enter_irq_off() conditionally calls > > > rcu_virt_note_context_switch(), but I can't immediately spot anything on the > > > exit side that corresponded with that, which looks suspicious. > > > > rcu_note_context_switch() is a point-in-time notification; it's not strictly > > necessary, but it may improve performance a bit by avoiding unnecessary IPIs > > from the RCU subsystem. > > > > There's no benefit from doing it when you're back from the guest, because at > > that point the CPU is just running normal kernel code. > > Do scheduling-clock interrupts from guest mode have the "user" parameter > set? If so, that would keep RCU happy. Are you referring to the user_mode() check in irqentry_enter()? If so I don't think it'll help, arm64 doesn't use that function. It directly calls enter_from_{user,kernel}_mode() through its custom entry/exit routines. Regards, -- Nicolás Sáenz 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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8E1EAC433EF for ; Fri, 17 Dec 2021 17:36:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Date:Cc:To:From:Subject:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=gIBC5+tKWLFlRVuAcNQodWLtWjw2bUV/3h57mBznhBo=; b=XeQl2mpZ9ezyad VYEewdZD1fdIJnshRs9MqlFVC4J1aLKqZHRQSmb6M1EWf/CwR28loti0WoXuMZHxVQl+dxuTo+WIx GIPLgnEJqphsZX6QnL8a2fDbBX4VTo1es9lICvNjR+7Ke0B0BmfOiqyKCdjZDiTxI8nEU8xhhyLpF CsufVNTK6EGKzt58tLGOjsR/yaGA2iB1rXDzAUwdda1sKB0Pn7RyMXJ726dLs8IVKKngROaSvxGpS tIcdDrnAWQp80yPTpXUxrcXkCi2T9xpNIzQFXjYu6v+e5VvGxPOeET1/JIDIIXS+1ZIz7QWEhoIQf H4jJa36sA1XWkOL8SISw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1myH7T-00BUz0-CY; Fri, 17 Dec 2021 17:34:14 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1myFy7-00B8eA-9o for linux-arm-kernel@lists.infradead.org; Fri, 17 Dec 2021 16:20:29 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639758024; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yeSLiX88ywUnJSn3OPy2dA6dAW/L5+XCxa+K1ZsSMkg=; b=NOw0MKAnc0pj9/G80WgJMwBpp8NVc+QKkyUM7G66odslwzBeYnP3Q7pUbc/pAUbqnzbtAw fJO+d2d2prpFVY4pFUuxR3DLhpSGDYPq2Lqy1Oj2WVDO0+FHLLU62MEEAcO+sP9zVqzve6 MKyalSIiDubC1LQmQZSNc/tbxIRehTY= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-312-vyS3zkAzOEepk5s9Gs5zQQ-1; Fri, 17 Dec 2021 11:20:23 -0500 X-MC-Unique: vyS3zkAzOEepk5s9Gs5zQQ-1 Received: by mail-wr1-f71.google.com with SMTP id o4-20020adfca04000000b0018f07ad171aso760923wrh.20 for ; Fri, 17 Dec 2021 08:20:23 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:user-agent:mime-version:content-transfer-encoding; bh=yeSLiX88ywUnJSn3OPy2dA6dAW/L5+XCxa+K1ZsSMkg=; b=qzEdXdetyhVli+t4InEk5KLry0Ytj/NlYekbWgvXyC9QKOkzSfvRRPPd4IRJPiwVnJ rbCPBB1EMz3ewesr39S/zKz/fqTUdWnqw7MLhu3gbqnhrX6WbdH+5j8Yvq8cIzgUFm5v 1YFXzdiMZln04o+NZf4ymJwhMuiXxxmyDMMksuKNTyFDkKtPaUqfPmHcpfj9mUBTlOLM zD4PIzQ/5ZfAVQYSyOOAQ96Vt9L9Y8w7OQ5Vh+d7ipa8NZn+LaADag6RT+CaN8fqA/oc 0T2YrD1ZG2o/9KwgXJuGbOSDaFK2g8dq32cVPs1q13gOKfun1XPwdtDyL97slxLkSyYV n/hQ== X-Gm-Message-State: AOAM530KolaImZO9WV7TsWnvinTTTi6TQkvNAVZe0p4S58SME73/gNey 6EwqBBn4u6vrvcghImtcQU5rwADdk9oEPc/NEcHxiG/ynLDRGrFnNCwiAEmf9rzB2uMFWsPpWOz YafkR73zuajFMT3YvbsFZPoOSC75VeIn9TLk= X-Received: by 2002:a5d:6483:: with SMTP id o3mr3128441wri.634.1639758022087; Fri, 17 Dec 2021 08:20:22 -0800 (PST) X-Google-Smtp-Source: ABdhPJwk2ba7Tbij6WYWb1HqhmTZxhP9T+f29JbPI5KYAluKtYZQtdJHeX0aXwhZAJkm79KXnc0PuQ== X-Received: by 2002:a5d:6483:: with SMTP id o3mr3128421wri.634.1639758021885; Fri, 17 Dec 2021 08:20:21 -0800 (PST) Received: from ?IPv6:2a0c:5a80:3511:9200:f938:102b:34c2:d5db? 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([2a0c:5a80:3511:9200:f938:102b:34c2:d5db]) by smtp.gmail.com with ESMTPSA id b10sm8204839wrg.19.2021.12.17.08.20.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Dec 2021 08:20:21 -0800 (PST) Message-ID: <27231550b5600072da918aa41c07404dea13590e.camel@redhat.com> Subject: Re: Possible nohz-full/RCU issue in arm64 KVM From: Nicolas Saenz Julienne To: paulmck@kernel.org, Paolo Bonzini Date: Fri, 17 Dec 2021 17:20:21 +0100 In-Reply-To: <20211217160749.GS641268@paulmck-ThinkPad-P17-Gen-1> References: <70f112072d9496d21901946ea82832d3ed3a8cb2.camel@redhat.com> <9ab8107f-ff41-6a9e-57e1-a261bea93aca@redhat.com> <20211217160749.GS641268@paulmck-ThinkPad-P17-Gen-1> User-Agent: Evolution 3.42.2 (3.42.2-1.fc35) MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=nsaenzju@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Mailman-Approved-At: Sun, 19 Dec 2021 07:12:12 -0500 Cc: maz , frederic , linux-kernel , rcu , Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu SGkgUGF1bCwKCk9uIEZyaSwgMjAyMS0xMi0xNyBhdCAwODowNyAtMDgwMCwgUGF1bCBFLiBNY0tl bm5leSB3cm90ZToKPiBPbiBGcmksIERlYyAxNywgMjAyMSBhdCAwNDo1NDoyMlBNICswMTAwLCBQ YW9sbyBCb256aW5pIHdyb3RlOgo+ID4gT24gMTIvMTcvMjEgMTU6MzgsIE1hcmsgUnV0bGFuZCB3 cm90ZToKPiA+ID4gRm9yIGV4YW1wbGUga3ZtX2d1ZXN0X2VudGVyX2lycW9mZigpIGNhbGxzIGd1 ZXN0X2VudGVyX2lycV9vZmYoKSB3aGljaCBjYWxscwo+ID4gPiB2dGltZV9hY2NvdW50X2d1ZXN0 X2VudGVyKCksIGJ1dCBrdm1fZ3Vlc3RfZXhpdF9pcnFvZmYoKSBkb2Vzbid0IGNhbGwKPiA+ID4g Z3Vlc3RfZXhpdF9pcnFfb2ZmKCkgYW5kIHRoZSBjYWxsIHRvIHZ0aW1lX2FjY291bnRfZ3Vlc3Rf ZXhpdCgpIGlzIG9wZW4tY29kZWQKPiA+ID4gZWxzZXdoZXJlLiBBbHNvLCBndWVzdF9lbnRlcl9p cnFfb2ZmKCkgY29uZGl0aW9uYWxseSBjYWxscwo+ID4gPiByY3VfdmlydF9ub3RlX2NvbnRleHRf c3dpdGNoKCksIGJ1dCBJIGNhbid0IGltbWVkaWF0ZWx5IHNwb3QgYW55dGhpbmcgb24gdGhlCj4g PiA+IGV4aXQgc2lkZSB0aGF0IGNvcnJlc3BvbmRlZCB3aXRoIHRoYXQsIHdoaWNoIGxvb2tzIHN1 c3BpY2lvdXMuCj4gPiAKPiA+IHJjdV9ub3RlX2NvbnRleHRfc3dpdGNoKCkgaXMgYSBwb2ludC1p bi10aW1lIG5vdGlmaWNhdGlvbjsgaXQncyBub3Qgc3RyaWN0bHkKPiA+IG5lY2Vzc2FyeSwgYnV0 IGl0IG1heSBpbXByb3ZlIHBlcmZvcm1hbmNlIGEgYml0IGJ5IGF2b2lkaW5nIHVubmVjZXNzYXJ5 IElQSXMKPiA+IGZyb20gdGhlIFJDVSBzdWJzeXN0ZW0uCj4gPiAKPiA+IFRoZXJlJ3Mgbm8gYmVu ZWZpdCBmcm9tIGRvaW5nIGl0IHdoZW4geW91J3JlIGJhY2sgZnJvbSB0aGUgZ3Vlc3QsIGJlY2F1 c2UgYXQKPiA+IHRoYXQgcG9pbnQgdGhlIENQVSBpcyBqdXN0IHJ1bm5pbmcgbm9ybWFsIGtlcm5l bCBjb2RlLgo+IAo+IERvIHNjaGVkdWxpbmctY2xvY2sgaW50ZXJydXB0cyBmcm9tIGd1ZXN0IG1v ZGUgaGF2ZSB0aGUgInVzZXIiIHBhcmFtZXRlcgo+IHNldD8gIElmIHNvLCB0aGF0IHdvdWxkIGtl ZXAgUkNVIGhhcHB5LgoKQXJlIHlvdSByZWZlcnJpbmcgdG8gdGhlIHVzZXJfbW9kZSgpIGNoZWNr IGluIGlycWVudHJ5X2VudGVyKCk/IElmIHNvIEkgZG9uJ3QKdGhpbmsgaXQnbGwgaGVscCwgYXJt NjQgZG9lc24ndCB1c2UgdGhhdCBmdW5jdGlvbi4gSXQgZGlyZWN0bHkgY2FsbHMKZW50ZXJfZnJv bV97dXNlcixrZXJuZWx9X21vZGUoKSB0aHJvdWdoIGl0cyBjdXN0b20gZW50cnkvZXhpdCByb3V0 aW5lcy4KClJlZ2FyZHMsCgotLSAKTmljb2zDoXMgU8OhZW56CgpfX19fX19fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fXwprdm1hcm0gbWFpbGluZyBsaXN0Cmt2bWFybUBs aXN0cy5jcy5jb2x1bWJpYS5lZHUKaHR0cHM6Ly9saXN0cy5jcy5jb2x1bWJpYS5lZHUvbWFpbG1h bi9saXN0aW5mby9rdm1hcm0K