From patchwork Fri Aug 2 14:50:09 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Price X-Patchwork-Id: 11073695 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 74463912 for ; Fri, 2 Aug 2019 14:51:35 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 61A5E28740 for ; Fri, 2 Aug 2019 14:51:35 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 55CAC28861; Fri, 2 Aug 2019 14:51:35 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B36E028740 for ; Fri, 2 Aug 2019 14:51:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2395049AbfHBOud (ORCPT ); Fri, 2 Aug 2019 10:50:33 -0400 Received: from foss.arm.com ([217.140.110.172]:53196 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387625AbfHBOuc (ORCPT ); Fri, 2 Aug 2019 10:50:32 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E5E831597; Fri, 2 Aug 2019 07:50:31 -0700 (PDT) Received: from e112269-lin.arm.com (e112269-lin.cambridge.arm.com [10.1.196.133]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0B7773F575; Fri, 2 Aug 2019 07:50:29 -0700 (PDT) From: Steven Price Cc: Steven Price , Catalin Marinas , Marc Zyngier , Paolo Bonzini , =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= , Russell King , Will Deacon , James Morse , Julien Thierry , Suzuki K Pouloze , kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/9] KVM: arm64: Document PV-time interface Date: Fri, 2 Aug 2019 15:50:09 +0100 Message-Id: <20190802145017.42543-2-steven.price@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190802145017.42543-1-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> MIME-Version: 1.0 To: unlisted-recipients:; (no To-header on input) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Introduce a paravirtualization interface for KVM/arm64 based on the "Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A. This only adds the details about "Stolen Time" as the details of "Live Physical Time" have not been fully agreed. User space can specify a reserved area of memory for the guest and inform KVM to populate the memory with information on time that the host kernel has stolen from the guest. A hypercall interface is provided for the guest to interrogate the hypervisor's support for this interface and the location of the shared memory structures. Signed-off-by: Steven Price --- Documentation/virtual/kvm/arm/pvtime.txt | 107 +++++++++++++++++++++++ 1 file changed, 107 insertions(+) create mode 100644 Documentation/virtual/kvm/arm/pvtime.txt diff --git a/Documentation/virtual/kvm/arm/pvtime.txt b/Documentation/virtual/kvm/arm/pvtime.txt new file mode 100644 index 000000000000..e6ae9799e1d5 --- /dev/null +++ b/Documentation/virtual/kvm/arm/pvtime.txt @@ -0,0 +1,107 @@ +Paravirtualized time support for arm64 +====================================== + +Arm specification DEN0057/A defined a standard for paravirtualised time +support for Aarch64 guests: + +https://developer.arm.com/docs/den0057/a + +KVM/Arm64 implements the stolen time part of this specification by providing +some hypervisor service calls to support a paravirtualized guest obtaining a +view of the amount of time stolen from its execution. + +Two new SMCCC compatible hypercalls are defined: + +PV_FEATURES 0xC5000020 +PV_TIME_ST 0xC5000022 + +These are only available in the SMC64/HVC64 calling convention as +paravirtualized time is not available to 32 bit Arm guests. + +PV_FEATURES + Function ID: (uint32) : 0xC5000020 + PV_func_id: (uint32) : Either PV_TIME_LPT or PV_TIME_ST + Return value: (int32) : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant + PV-time feature is supported by the hypervisor. + +PV_TIME_ST + Function ID: (uint32) : 0xC5000022 + Return value: (int64) : IPA of the stolen time data structure for this + (V)CPU. On failure: + NOT_SUPPORTED (-1) + +Stolen Time +----------- + +The structure pointed to by the PV_TIME_ST hypercall is as follows: + + Field | Byte Length | Byte Offset | Description + ----------- | ----------- | ----------- | -------------------------- + Revision | 4 | 0 | Must be 0 for version 0.1 + Attributes | 4 | 4 | Must be 0 + Stolen time | 8 | 8 | Stolen time in unsigned + | | | nanoseconds indicating how + | | | much time this VCPU thread + | | | was involuntarily not + | | | running on a physical CPU. + +The structure will be updated by the hypervisor periodically as time is stolen +from the VCPU. It will be present within a reserved region of the normal +memory given to the guest. The guest should not attempt to write into this +memory. There is a structure by VCPU of the guest. + +User space interface +==================== + +User space can request that KVM provide the paravirtualized time interface to +a guest by creating a KVM_DEV_TYPE_ARM_PV_TIME device, for example: + + struct kvm_create_device pvtime_device = { + .type = KVM_DEV_TYPE_ARM_PV_TIME, + .attr = 0, + .flags = 0, + }; + + pvtime_fd = ioctl(vm_fd, KVM_CREATE_DEVICE, &pvtime_device); + +The guest IPA of the structures must be given to KVM. This is the base address +of an array of stolen time structures (one for each VCPU). For example: + + struct kvm_device_attr st_base = { + .group = KVM_DEV_ARM_PV_TIME_PADDR, + .attr = KVM_DEV_ARM_PV_TIME_ST, + .addr = (u64)(unsigned long)&st_paddr + }; + + ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base); + +For migration (or save/restore) of a guest it is necessary to save the contents +of the shared page(s) and later restore them. KVM_DEV_ARM_PV_TIME_STATE_SIZE +provides the size of this data and KVM_DEV_ARM_PV_TIME_STATE allows the state +to be read/written. + +It is also necessary for the physical address to be set identically when +restoring. + + void *save_state(int fd, u64 attr, u32 *size) { + struct kvm_device_attr get_size = { + .group = KVM_DEV_ARM_PV_TIME_STATE_SIZE, + .attr = attr, + .addr = (u64)(unsigned long)size + }; + + ioctl(fd, KVM_GET_DEVICE_ATTR, get_size); + + void *buffer = malloc(*size); + + struct kvm_device_attr get_state = { + .group = KVM_DEV_ARM_PV_TIME_STATE, + .attr = attr, + .addr = (u64)(unsigned long)size + }; + + ioctl(fd, KVM_GET_DEVICE_ATTR, buffer); + } + + void *st_state = save_state(pvtime_fd, KVM_DEV_ARM_PV_TIME_ST, &st_size); +