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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 1FC4BC433E0 for ; Tue, 2 Feb 2021 13:55:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6F4A64FC5 for ; Tue, 2 Feb 2021 13:55:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233338AbhBBNzD (ORCPT ); Tue, 2 Feb 2021 08:55:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:43044 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233248AbhBBNwv (ORCPT ); Tue, 2 Feb 2021 08:52:51 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (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 5F05B64FC8; Tue, 2 Feb 2021 13:43:50 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1l6vy8-00BVL3-Fe; Tue, 02 Feb 2021 13:43:48 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 02 Feb 2021 13:43:48 +0000 From: Marc Zyngier To: Jianyong Wu Cc: netdev@vger.kernel.org, yangbo.lu@nxp.com, john.stultz@linaro.org, tglx@linutronix.de, pbonzini@redhat.com, richardcochran@gmail.com, Mark.Rutland@arm.com, will@kernel.org, suzuki.poulose@arm.com, Andre.Przywara@arm.com, steven.price@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Steve.Capper@arm.com, justin.he@arm.com, nd@arm.com Subject: Re: [PATCH v16 8/9] doc: add ptp_kvm introduction for arm64 support In-Reply-To: <20201209060932.212364-9-jianyong.wu@arm.com> References: <20201209060932.212364-1-jianyong.wu@arm.com> <20201209060932.212364-9-jianyong.wu@arm.com> User-Agent: Roundcube Webmail/1.4.10 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: jianyong.wu@arm.com, netdev@vger.kernel.org, yangbo.lu@nxp.com, john.stultz@linaro.org, tglx@linutronix.de, pbonzini@redhat.com, richardcochran@gmail.com, Mark.Rutland@arm.com, will@kernel.org, suzuki.poulose@arm.com, Andre.Przywara@arm.com, steven.price@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Steve.Capper@arm.com, justin.he@arm.com, nd@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2020-12-09 06:09, Jianyong Wu wrote: > PTP_KVM implementation depends on hypercall using SMCCC. So we > introduce a new SMCCC service ID. This doc explains how does the > ID define and how does PTP_KVM works on arm/arm64. > > Signed-off-by: Jianyong Wu > --- > Documentation/virt/kvm/api.rst | 9 +++++++ > Documentation/virt/kvm/arm/index.rst | 1 + > Documentation/virt/kvm/arm/ptp_kvm.rst | 31 +++++++++++++++++++++++ > Documentation/virt/kvm/timekeeping.rst | 35 ++++++++++++++++++++++++++ > 4 files changed, 76 insertions(+) > create mode 100644 Documentation/virt/kvm/arm/ptp_kvm.rst > > diff --git a/Documentation/virt/kvm/api.rst > b/Documentation/virt/kvm/api.rst > index e00a66d72372..3769cc2f7d9c 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -6390,3 +6390,12 @@ When enabled, KVM will disable paravirtual > features provided to the > guest according to the bits in the KVM_CPUID_FEATURES CPUID leaf > (0x40000001). Otherwise, a guest may use the paravirtual features > regardless of what has actually been exposed through the CPUID leaf. > + > +8.27 KVM_CAP_PTP_KVM > +-------------------- > + > +:Architectures: arm64 > + > +This capability indicates that KVM virtual PTP service is supported in > host. > +It must company with the implementation of KVM virtual PTP service in > host > +so VMM can probe if there is the service in host by checking this > capability. This reads a bit odd. I came up with the following: +This capability indicates that the KVM virtual PTP service is +supported in the host. A VMM can check whether the service is +available to the guest on migration. > diff --git a/Documentation/virt/kvm/arm/index.rst > b/Documentation/virt/kvm/arm/index.rst > index 3e2b2aba90fc..78a9b670aafe 100644 > --- a/Documentation/virt/kvm/arm/index.rst > +++ b/Documentation/virt/kvm/arm/index.rst > @@ -10,3 +10,4 @@ ARM > hyp-abi > psci > pvtime > + ptp_kvm > diff --git a/Documentation/virt/kvm/arm/ptp_kvm.rst > b/Documentation/virt/kvm/arm/ptp_kvm.rst > new file mode 100644 > index 000000000000..d729c1388a5c > --- /dev/null > +++ b/Documentation/virt/kvm/arm/ptp_kvm.rst > @@ -0,0 +1,31 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +PTP_KVM support for arm/arm64 > +============================= > + > +PTP_KVM is used for time sync between guest and host in a high > precision. > +It needs to get the wall time and counter value from the host and > transfer these > +to guest via hypercall service. So one more hypercall service has been > added. > + > +This new SMCCC hypercall is defined as: It won't be new anymore the minute this is merged. > + > +* ARM_SMCCC_HYP_KVM_PTP_FUNC_ID: 0x86000001 > + > +As both 32 and 64-bits ptp_kvm client should be supported, we choose > SMC32/HVC32 > +calling convention. > + > +ARM_SMCCC_HYP_KVM_PTP_FUNC_ID: > + > + ============= ========== ========== > + Function ID: (uint32) 0x86000001 > + Arguments: (uint32) ARM_PTP_PHY_COUNTER(1) or > ARM_PTP_VIRT_COUNTER(0) > + which indicate acquiring physical > counter or > + virtual counter respectively. > + Return Value: val0(uint32) NOT_SUPPORTED(-1) or upper 32 bits > of wall clock time(64-bits). > + val1(uint32) Lower 32 bits of wall clock time. > + val2(uint32) Upper 32 bits of counter > cycle(64-bits). > + val3(uint32) Lower 32 bits of counter cycle. > + Endianness: No Restrictions. > + ============= ========== ========== > + > +More info see section 5 in Documentation/virt/kvm/timekeeping.rst. I've tidied this up like this: diff --git a/Documentation/virt/kvm/arm/ptp_kvm.rst b/Documentation/virt/kvm/arm/ptp_kvm.rst index d729c1388a5c..68cffb50d8bf 100644 --- a/Documentation/virt/kvm/arm/ptp_kvm.rst +++ b/Documentation/virt/kvm/arm/ptp_kvm.rst @@ -3,29 +3,23 @@ PTP_KVM support for arm/arm64 ============================= -PTP_KVM is used for time sync between guest and host in a high precision. -It needs to get the wall time and counter value from the host and transfer these -to guest via hypercall service. So one more hypercall service has been added. - -This new SMCCC hypercall is defined as: +PTP_KVM is used for high precision time sync between host and guests. +It relies on transferring the wall clock and counter value from the +host to the guest using a KVM-specific hypercall. * ARM_SMCCC_HYP_KVM_PTP_FUNC_ID: 0x86000001 -As both 32 and 64-bits ptp_kvm client should be supported, we choose SMC32/HVC32 -calling convention. - -ARM_SMCCC_HYP_KVM_PTP_FUNC_ID: +This hypercall uses the SMC32/HVC32 calling convention: +ARM_SMCCC_HYP_KVM_PTP_FUNC_ID ============= ========== ========== Function ID: (uint32) 0x86000001 - Arguments: (uint32) ARM_PTP_PHY_COUNTER(1) or ARM_PTP_VIRT_COUNTER(0) - which indicate acquiring physical counter or - virtual counter respectively. - Return Value: val0(uint32) NOT_SUPPORTED(-1) or upper 32 bits of wall clock time(64-bits). - val1(uint32) Lower 32 bits of wall clock time. - val2(uint32) Upper 32 bits of counter cycle(64-bits). - val3(uint32) Lower 32 bits of counter cycle. + Arguments: (uint32) KVM_PTP_VIRT_COUNTER(0) + KVM_PTP_PHYS_COUNTER(1) + Return Values: (int32) NOT_SUPPORTED(-1) on error, or + (uint32) Upper 32 bits of wall clock time (r0) + (uint32) Lower 32 bits of wall clock time (r1) + (uint32) Upper 32 bits of counter (r2) + (uint32) Lower 32 bits of counter (r3) Endianness: No Restrictions. ============= ========== ========== - -More info see section 5 in Documentation/virt/kvm/timekeeping.rst. > diff --git a/Documentation/virt/kvm/timekeeping.rst > b/Documentation/virt/kvm/timekeeping.rst > index 21ae7efa29ba..c81383e38372 100644 > --- a/Documentation/virt/kvm/timekeeping.rst > +++ b/Documentation/virt/kvm/timekeeping.rst > @@ -13,6 +13,7 @@ Timekeeping Virtualization for X86-Based > Architectures > 2) Timing Devices > 3) TSC Hardware > 4) Virtualization Problems > + 5) KVM virtual PTP clock > > 1. Overview > =========== > @@ -643,3 +644,37 @@ by using CPU utilization itself as a signalling > channel. Preventing such > problems would require completely isolated virtual time which may not > track > real time any longer. This may be useful in certain security or QA > contexts, > but in general isn't recommended for real-world deployment scenarios. > + > +5. KVM virtual PTP clock > +======================== > + > +NTP (Network Time Protocol) is often used to sync time in a VM. > Unfortunately, > +the precision of NTP is limited due to unknown delays in the network. > + > +KVM virtual PTP clock (PTP_KVM) offers another way to sync time in VM; > use the > +host's clock rather than one from a remote machine. Having a > synchronization > +mechanism for the virtualization environment allows us to keep all the > guests > +running on the same host in sync. > +In general, the delay of communication between host and guest is quite > +small, so ptp_kvm can offer time sync precision up to in order of > nanoseconds. > +Please keep in mind that ptp_kvm just limits itself to be a channel > which > +transmits the remote clock from host to guest. An application, eg. > chrony, is > +needed in usersapce of VM in order to set the guest time. > + > +After ptp_kvm is initialized, there will be a new device node under > /dev called > +ptp%d. A guest userspace service, like chrony, can use this device to > get host > +walltime, sometimes also counter cycle, which depends on the service > it calls. > +Then this guest userspace service can use those data to do the time > sync for > +the guest. > +The following is the work flow of ptp_kvm: > + > +a) time sync service in guest userspace call ioctl on ptp device > /dev/ptp%d. > +b) ptp_kvm module in guest receives this request then invokes > hypercall to > + route into host kernel to request host's walltime/counter cycle. > +c) ptp_kvm hypercall service on the host responds to the request and > sends data > + back. > +d) ptp in guest copies the data to userspace. > + > +ptp_kvm consists of components running on the guest and host. Step 2 > consists of > +a guest driver making a hypercall whilst step 3 involves the > hypervisor responding > +with information. I don't think we need any of this here, as the whole file focuses on x86-specific issues for timekeeping. If we want to document KVM PTP, this should probably be a separate document. Thanks, M. -- Jazz is not dead. It just smells funny...