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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 6BA5DC04EB8 for ; Mon, 10 Dec 2018 12:54:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3996720855 for ; Mon, 10 Dec 2018 12:54:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3996720855 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.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 S1726928AbeLJMyX (ORCPT ); Mon, 10 Dec 2018 07:54:23 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53286 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726392AbeLJMyW (ORCPT ); Mon, 10 Dec 2018 07:54:22 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3427F3082E4E; Mon, 10 Dec 2018 12:54:22 +0000 (UTC) Received: from vitty.brq.redhat.com.redhat.com (unknown [10.43.2.155]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0A7E25DA63; Mon, 10 Dec 2018 12:54:19 +0000 (UTC) From: Vitaly Kuznetsov To: Roman Kagan Cc: "kvm\@vger.kernel.org" , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , "linux-kernel\@vger.kernel.org" , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , "x86\@kernel.org" , "Michael Kelley \(EOSG\)" Subject: Re: [PATCH v2 3/4] x86/kvm/hyper-v: direct mode for synthetic timers In-Reply-To: <20181210120637.GA13294@rkaganb.sw.ru> References: <20181126154732.23025-1-vkuznets@redhat.com> <20181126154732.23025-4-vkuznets@redhat.com> <20181210120637.GA13294@rkaganb.sw.ru> Date: Mon, 10 Dec 2018 13:54:18 +0100 Message-ID: <87va41czk5.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Mon, 10 Dec 2018 12:54:22 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Roman Kagan writes: > On Mon, Nov 26, 2018 at 04:47:31PM +0100, Vitaly Kuznetsov wrote: >> Turns out Hyper-V on KVM (as of 2016) will only use synthetic timers >> if direct mode is available. With direct mode we notify the guest by >> asserting APIC irq instead of sending a SynIC message. >> >> The implementation uses existing vec_bitmap for letting lapic code >> know that we're interested in the particular IRQ's EOI request. We assume >> that the same APIC irq won't be used by the guest for both direct mode >> stimer and as sint source (especially with AutoEOI semantics). It is >> unclear how things should be handled if that's not true. >> >> Direct mode is also somewhat less expensive; in my testing >> stimer_send_msg() takes not less than 1500 cpu cycles and >> stimer_notify_direct() can usually be done in 300-400. WS2016 without >> Hyper-V, however, always sticks to non-direct version. >> >> Signed-off-by: Vitaly Kuznetsov >> --- >> - Changes since v1: avoid open-coding stimer_mark_pending() in >> kvm_hv_synic_send_eoi() [Paolo Bonzini] >> --- >> arch/x86/kvm/hyperv.c | 67 +++++++++++++++++++++++++++++++++++----- >> arch/x86/kvm/trace.h | 10 +++--- >> arch/x86/kvm/x86.c | 1 + >> include/uapi/linux/kvm.h | 1 + >> 4 files changed, 67 insertions(+), 12 deletions(-) >> >> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c >> index eaec15c738df..9533133be566 100644 >> --- a/arch/x86/kvm/hyperv.c >> +++ b/arch/x86/kvm/hyperv.c >> @@ -38,6 +38,9 @@ >> >> #define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 64) >> >> +static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer, >> + bool vcpu_kick); >> + >> static inline u64 synic_read_sint(struct kvm_vcpu_hv_synic *synic, int sint) >> { >> return atomic64_read(&synic->sint[sint]); >> @@ -53,8 +56,21 @@ static inline int synic_get_sint_vector(u64 sint_value) >> static bool synic_has_vector_connected(struct kvm_vcpu_hv_synic *synic, >> int vector) >> { >> + struct kvm_vcpu *vcpu = synic_to_vcpu(synic); >> + struct kvm_vcpu_hv *hv_vcpu = vcpu_to_hv_vcpu(vcpu); >> + struct kvm_vcpu_hv_stimer *stimer; >> int i; >> >> + for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++) { >> + stimer = &hv_vcpu->stimer[i]; >> + if (stimer->config.enable && stimer->config.direct_mode && >> + stimer->config.apic_vector == vector) >> + return true; >> + } >> + >> + if (vector < HV_SYNIC_FIRST_VALID_VECTOR) >> + return false; >> + >> for (i = 0; i < ARRAY_SIZE(synic->sint); i++) { >> if (synic_get_sint_vector(synic_read_sint(synic, i)) == vector) >> return true; >> @@ -80,14 +96,14 @@ static bool synic_has_vector_auto_eoi(struct kvm_vcpu_hv_synic *synic, >> static void synic_update_vector(struct kvm_vcpu_hv_synic *synic, >> int vector) >> { >> - if (vector < HV_SYNIC_FIRST_VALID_VECTOR) >> - return; >> - >> if (synic_has_vector_connected(synic, vector)) >> __set_bit(vector, synic->vec_bitmap); >> else >> __clear_bit(vector, synic->vec_bitmap); >> >> + if (vector < HV_SYNIC_FIRST_VALID_VECTOR) >> + return; >> + > > Just noticed that the patch seems to assume that "direct" timers are > allowed to use any vectors including 0-15. I guess this is incorrect, > and instead stimer_set_config should error out on direct mode with a > vector less than HV_SYNIC_FIRST_VALID_VECTOR. The spec is really vague about this and I'm not sure that this has anything to do with HV_SYNIC_FIRST_VALID_VECTOR (as these are actually not "synic" vectors, I *think* that SynIC doesn't even need to be enabled to make them work). I checked and Hyper-V 2016 uses vector '0xff', not sure if it proves your point :-) Do you envision any issues in KVM if we keep allowing vectors < HV_SYNIC_FIRST_VALID_VECTOR? -- Vitaly