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=-9.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,T_DKIMWL_WL_HIGH,USER_AGENT_GIT autolearn=unavailable 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 9F168C43219 for ; Thu, 2 May 2019 15:34:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 70E8E214DA for ; Thu, 2 May 2019 15:34:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556811271; bh=65ruzGAENGirINjoKdB+RVXEuqlPR6pfOjvTO9q47JE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=RS6WQtAUBr6Txz5B70yqqGnTCbm5lKS8skmUvCcbC5K6O6GR81hl+XxnP8Aawgs84 LzDXP5s2mgspgitR0ajJtbogGCIw2iliftBEBwuaqKPPNcrEQqQqI3fbaHYbSlw+BR 6lIZlHIypM8C+NFgqJqv7xxeChFx3xkVpFKgiDXs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726415AbfEBPe0 (ORCPT ); Thu, 2 May 2019 11:34:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:51638 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729109AbfEBPcH (ORCPT ); Thu, 2 May 2019 11:32:07 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1F5F820C01; Thu, 2 May 2019 15:32:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556811126; bh=65ruzGAENGirINjoKdB+RVXEuqlPR6pfOjvTO9q47JE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OBr86lxsktL/c+5BGZskf999eeQMaLUmlSDDck3wPGM4vtchMglNX9zL9g22QMDFK 7Yms0jrcRZ+8qhBwFeAbEkdMNUVWqqqqukd2blCtcLxeKFA3diIXbFxCIZdirGkuD9 S2rJYyVQJI9ooazTJAI4bNrbEt/i/PUoqUlzO4PY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vitaly Kuznetsov , Paolo Bonzini , "Sasha Levin (Microsoft)" Subject: [PATCH 5.0 085/101] x86/kvm/hyper-v: avoid spurious pending stimer on vCPU init Date: Thu, 2 May 2019 17:21:27 +0200 Message-Id: <20190502143345.557664615@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190502143339.434882399@linuxfoundation.org> References: <20190502143339.434882399@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org [ Upstream commit 013cc6ebbf41496ce4badedd71ea6d4a6d198c14 ] When userspace initializes guest vCPUs it may want to zero all supported MSRs including Hyper-V related ones including HV_X64_MSR_STIMERn_CONFIG/ HV_X64_MSR_STIMERn_COUNT. With commit f3b138c5d89a ("kvm/x86: Update SynIC timers on guest entry only") we began doing stimer_mark_pending() unconditionally on every config change. The issue I'm observing manifests itself as following: - Qemu writes 0 to STIMERn_{CONFIG,COUNT} MSRs and marks all stimers as pending in stimer_pending_bitmap, arms KVM_REQ_HV_STIMER; - kvm_hv_has_stimer_pending() starts returning true; - kvm_vcpu_has_events() starts returning true; - kvm_arch_vcpu_runnable() starts returning true; - when kvm_arch_vcpu_ioctl_run() gets into (vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED) case: - kvm_vcpu_block() gets in 'kvm_vcpu_check_block(vcpu) < 0' and returns immediately, avoiding normal wait path; - -EAGAIN is returned from kvm_arch_vcpu_ioctl_run() immediately forcing userspace to retry. So instead of normal wait path we get a busy loop on all secondary vCPUs before they get INIT signal. This seems to be undesirable, especially given that this happens even when Hyper-V extensions are not used. Generally, it seems to be pointless to mark an stimer as pending in stimer_pending_bitmap and arm KVM_REQ_HV_STIMER as the only thing kvm_hv_process_stimers() will do is clear the corresponding bit. We may just not mark disabled timers as pending instead. Fixes: f3b138c5d89a ("kvm/x86: Update SynIC timers on guest entry only") Signed-off-by: Vitaly Kuznetsov Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin (Microsoft) --- arch/x86/kvm/hyperv.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index 89d20ed1d2e8..371c669696d7 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -526,7 +526,9 @@ static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config, new_config.enable = 0; stimer->config.as_uint64 = new_config.as_uint64; - stimer_mark_pending(stimer, false); + if (stimer->config.enable) + stimer_mark_pending(stimer, false); + return 0; } @@ -542,7 +544,10 @@ static int stimer_set_count(struct kvm_vcpu_hv_stimer *stimer, u64 count, stimer->config.enable = 0; else if (stimer->config.auto_enable) stimer->config.enable = 1; - stimer_mark_pending(stimer, false); + + if (stimer->config.enable) + stimer_mark_pending(stimer, false); + return 0; } -- 2.19.1