From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.7 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 05A067D2F0 for ; Thu, 8 Aug 2019 15:29:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727649AbfHHP3g (ORCPT ); Thu, 8 Aug 2019 11:29:36 -0400 Received: from foss.arm.com ([217.140.110.172]:34992 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730768AbfHHP3g (ORCPT ); Thu, 8 Aug 2019 11:29:36 -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 6E98A1596; Thu, 8 Aug 2019 08:29:35 -0700 (PDT) Received: from [10.1.196.133] (e112269-lin.cambridge.arm.com [10.1.196.133]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8A89F3F706; Thu, 8 Aug 2019 08:29:33 -0700 (PDT) Subject: Re: [PATCH 9/9] arm64: Retrieve stolen time as paravirtualized guest To: Marc Zyngier Cc: Catalin Marinas , 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 References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-10-steven.price@arm.com> <20190804105353.5e9824dc@why> From: Steven Price Message-ID: Date: Thu, 8 Aug 2019 16:29:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190804105353.5e9824dc@why> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 04/08/2019 10:53, Marc Zyngier wrote: > On Fri, 2 Aug 2019 15:50:17 +0100 > Steven Price wrote: > >> Enable paravirtualization features when running under a hypervisor >> supporting the PV_TIME_ST hypercall. >> >> For each (v)CPU, we ask the hypervisor for the location of a shared >> page which the hypervisor will use to report stolen time to us. We set >> pv_time_ops to the stolen time function which simply reads the stolen >> value from the shared page for a VCPU. We guarantee single-copy >> atomicity using READ_ONCE which means we can also read the stolen >> time for another VCPU than the currently running one while it is >> potentially being updated by the hypervisor. >> >> Signed-off-by: Steven Price >> --- >> arch/arm64/kernel/Makefile | 1 + >> arch/arm64/kernel/kvm.c | 155 +++++++++++++++++++++++++++++++++++++ > > nit: Why not using paravirt.c, which clearly states what it does? The > alternative would be to name it kvm-pv.c. I can move it to paravirt.c - seems reasonable. >> include/linux/cpuhotplug.h | 1 + >> 3 files changed, 157 insertions(+) >> create mode 100644 arch/arm64/kernel/kvm.c >> >> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile >> index 478491f07b4f..eb36edf9b930 100644 >> --- a/arch/arm64/kernel/Makefile >> +++ b/arch/arm64/kernel/Makefile >> @@ -63,6 +63,7 @@ obj-$(CONFIG_CRASH_CORE) += crash_core.o >> obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o >> obj-$(CONFIG_ARM64_SSBD) += ssbd.o >> obj-$(CONFIG_ARM64_PTR_AUTH) += pointer_auth.o >> +obj-$(CONFIG_PARAVIRT) += kvm.o >> >> obj-y += vdso/ probes/ >> obj-$(CONFIG_COMPAT_VDSO) += vdso32/ >> diff --git a/arch/arm64/kernel/kvm.c b/arch/arm64/kernel/kvm.c >> new file mode 100644 >> index 000000000000..245398c79dae >> --- /dev/null >> +++ b/arch/arm64/kernel/kvm.c >> @@ -0,0 +1,155 @@ >> +// SPDX-License-Identifier: GPL-2.0 >> +// Copyright (C) 2019 Arm Ltd. >> + >> +#define pr_fmt(fmt) "kvmarm-pv: " fmt >> + >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> + >> +#include >> +#include >> +#include >> + >> +struct kvmarm_stolen_time_region { >> + struct pvclock_vcpu_stolen_time_info *kaddr; >> +}; >> + >> +static DEFINE_PER_CPU(struct kvmarm_stolen_time_region, stolen_time_region); >> + >> +static bool steal_acc = true; >> +static int __init parse_no_stealacc(char *arg) >> +{ >> + steal_acc = false; >> + return 0; >> +} >> +early_param("no-steal-acc", parse_no_stealacc); >> + >> +/* return stolen time in ns by asking the hypervisor */ >> +static u64 kvm_steal_clock(int cpu) >> +{ >> + struct kvmarm_stolen_time_region *reg; >> + >> + reg = per_cpu_ptr(&stolen_time_region, cpu); >> + if (!reg->kaddr) { >> + pr_warn_once("stolen time enabled but not configured for cpu %d\n", >> + cpu); >> + return 0; >> + } >> + >> + return le64_to_cpu(READ_ONCE(reg->kaddr->stolen_time)); >> +} >> + >> +static int disable_stolen_time_current_cpu(void) >> +{ >> + struct kvmarm_stolen_time_region *reg; >> + >> + reg = this_cpu_ptr(&stolen_time_region); >> + if (!reg->kaddr) >> + return 0; >> + >> + memunmap(reg->kaddr); >> + memset(reg, 0, sizeof(*reg)); >> + >> + return 0; >> +} >> + >> +static int stolen_time_dying_cpu(unsigned int cpu) >> +{ >> + return disable_stolen_time_current_cpu(); >> +} >> + >> +static int init_stolen_time_cpu(unsigned int cpu) >> +{ >> + struct kvmarm_stolen_time_region *reg; >> + struct arm_smccc_res res; >> + >> + reg = this_cpu_ptr(&stolen_time_region); >> + >> + if (reg->kaddr) >> + return 0; > > Can this actually happen? It'd take two CPU_UP calls from the HP > notifiers to get in that situation... Yes, something would have to be very broken for that to happen - I'll remove this check. >> + >> + arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_ST, &res); >> + >> + if ((long)res.a0 < 0) >> + return -EINVAL; >> + >> + reg->kaddr = memremap(res.a0, >> + sizeof(struct pvclock_vcpu_stolen_time_info), >> + MEMREMAP_WB); >> + >> + if (reg->kaddr == NULL) { >> + pr_warn("Failed to map stolen time data structure\n"); >> + return -EINVAL; > > -ENOMEM is the expected return code. Ok >> + } >> + >> + if (le32_to_cpu(reg->kaddr->revision) != 0 || >> + le32_to_cpu(reg->kaddr->attributes) != 0) { >> + pr_warn("Unexpected revision or attributes in stolen time data\n"); >> + return -ENXIO; >> + } >> + >> + return 0; >> +} >> + >> +static int kvm_arm_init_stolen_time(void) >> +{ >> + int ret; >> + >> + ret = cpuhp_setup_state(CPUHP_AP_ARM_KVMPV_STARTING, >> + "hypervisor/kvmarm/pv:starting", >> + init_stolen_time_cpu, stolen_time_dying_cpu); >> + if (ret < 0) >> + return ret; >> + return 0; >> +} >> + >> +static bool has_kvm_steal_clock(void) >> +{ >> + struct arm_smccc_res res; >> + >> + /* To detect the presence of PV time support we require SMCCC 1.1+ */ >> + if (psci_ops.smccc_version < SMCCC_VERSION_1_1) >> + return false; >> + >> + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID, >> + ARM_SMCCC_HV_PV_FEATURES, &res); >> + >> + if (res.a0 != SMCCC_RET_SUCCESS) >> + return false; >> + >> + arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_FEATURES, >> + ARM_SMCCC_HV_PV_TIME_ST, &res); >> + >> + if (res.a0 != SMCCC_RET_SUCCESS) >> + return false; >> + >> + return true; >> +} >> + >> +static int __init kvm_guest_init(void) >> +{ >> + int ret = 0; >> + >> + if (!has_kvm_steal_clock()) >> + return 0; >> + >> + ret = kvm_arm_init_stolen_time(); >> + if (ret) >> + return ret; >> + >> + pv_ops.time.steal_clock = kvm_steal_clock; >> + >> + static_key_slow_inc(¶virt_steal_enabled); >> + if (steal_acc) >> + static_key_slow_inc(¶virt_steal_rq_enabled); >> + >> + pr_info("using stolen time PV\n"); >> + >> + return 0; >> +} >> +early_initcall(kvm_guest_init); > > Is there any reason why we wouldn't directly call into this rather than > using an initcall? I'm not sure where the direct call would go - any pointers? Thanks, Steve >> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h >> index 068793a619ca..89d75edb5750 100644 >> --- a/include/linux/cpuhotplug.h >> +++ b/include/linux/cpuhotplug.h >> @@ -136,6 +136,7 @@ enum cpuhp_state { >> /* Must be the last timer callback */ >> CPUHP_AP_DUMMY_TIMER_STARTING, >> CPUHP_AP_ARM_XEN_STARTING, >> + CPUHP_AP_ARM_KVMPV_STARTING, >> CPUHP_AP_ARM_CORESIGHT_STARTING, >> CPUHP_AP_ARM64_ISNDEP_STARTING, >> CPUHP_AP_SMPCFD_DYING, > > > Thanks, > > M. >