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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 BBFF0C32754 for ; Mon, 5 Aug 2019 14:18:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9C9862173B for ; Mon, 5 Aug 2019 14:18:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729087AbfHEOSI (ORCPT ); Mon, 5 Aug 2019 10:18:08 -0400 Received: from foss.arm.com ([217.140.110.172]:50078 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726508AbfHEOSI (ORCPT ); Mon, 5 Aug 2019 10:18:08 -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 67451337; Mon, 5 Aug 2019 07:18:07 -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 1F43B3F706; Mon, 5 Aug 2019 07:18:05 -0700 (PDT) Subject: Re: [PATCH 4/9] KVM: arm64: Support stolen time reporting via shared structure To: Marc Zyngier Cc: kvm@vger.kernel.org, linux-doc@vger.kernel.org, Catalin Marinas , linux-kernel@vger.kernel.org, Russell King , Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-5-steven.price@arm.com> <20190803185817.11285b2a@why> <20190803191303.02e9bcc9@why> From: Steven Price Message-ID: <4a373dc5-4a6b-efc6-4309-e7180eb0c696@arm.com> Date: Mon, 5 Aug 2019 15:18:04 +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: <20190803191303.02e9bcc9@why> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 03/08/2019 19:13, Marc Zyngier wrote: > On Sat, 3 Aug 2019 18:58:17 +0100 > Marc Zyngier wrote: > >> On Fri, 2 Aug 2019 15:50:12 +0100 >> Steven Price wrote: >> >>> Implement the service call for configuring a shared structre between a >>> VCPU and the hypervisor in which the hypervisor can write the time >>> stolen from the VCPU's execution time by other tasks on the host. >>> >>> The hypervisor allocates memory which is placed at an IPA chosen by user >>> space. The hypervisor then uses WRITE_ONCE() to update the shared >>> structre ensuring single copy atomicity of the 64-bit unsigned value >>> that reports stolen time in nanoseconds. >>> >>> Whenever stolen time is enabled by the guest, the stolen time counter is >>> reset. >>> >>> The stolen time itself is retrieved from the sched_info structure >>> maintained by the Linux scheduler code. We enable SCHEDSTATS when >>> selecting KVM Kconfig to ensure this value is meaningful. >>> >>> Signed-off-by: Steven Price >>> --- >>> arch/arm64/include/asm/kvm_host.h | 13 +++++- >>> arch/arm64/kvm/Kconfig | 1 + >>> include/kvm/arm_hypercalls.h | 1 + >>> include/linux/kvm_types.h | 2 + >>> virt/kvm/arm/arm.c | 18 ++++++++ >>> virt/kvm/arm/hypercalls.c | 70 +++++++++++++++++++++++++++++++ >>> 6 files changed, 104 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h >>> index f656169db8c3..78f270190d43 100644 >>> --- a/arch/arm64/include/asm/kvm_host.h >>> +++ b/arch/arm64/include/asm/kvm_host.h >>> @@ -44,6 +44,7 @@ >>> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP) >>> #define KVM_REQ_IRQ_PENDING KVM_ARCH_REQ(1) >>> #define KVM_REQ_VCPU_RESET KVM_ARCH_REQ(2) >>> +#define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3) >>> >>> DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use); >>> >>> @@ -83,6 +84,11 @@ struct kvm_arch { >>> >>> /* Mandated version of PSCI */ >>> u32 psci_version; >>> + >>> + struct kvm_arch_pvtime { >>> + void *st; >>> + gpa_t st_base; >>> + } pvtime; >>> }; >>> >>> #define KVM_NR_MEM_OBJS 40 >>> @@ -338,8 +344,13 @@ struct kvm_vcpu_arch { >>> /* True when deferrable sysregs are loaded on the physical CPU, >>> * see kvm_vcpu_load_sysregs and kvm_vcpu_put_sysregs. */ >>> bool sysregs_loaded_on_cpu; >>> -}; >>> >>> + /* Guest PV state */ >>> + struct { >>> + u64 steal; >>> + u64 last_steal; >>> + } steal; >>> +}; >>> /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */ >>> #define vcpu_sve_pffr(vcpu) ((void *)((char *)((vcpu)->arch.sve_state) + \ >>> sve_ffr_offset((vcpu)->arch.sve_max_vl))) >>> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig >>> index a67121d419a2..d8b88e40d223 100644 >>> --- a/arch/arm64/kvm/Kconfig >>> +++ b/arch/arm64/kvm/Kconfig >>> @@ -39,6 +39,7 @@ config KVM >>> select IRQ_BYPASS_MANAGER >>> select HAVE_KVM_IRQ_BYPASS >>> select HAVE_KVM_VCPU_RUN_PID_CHANGE >>> + select SCHEDSTATS >>> ---help--- >>> Support hosting virtualized guest machines. >>> We don't support KVM with 16K page tables yet, due to the multiple >>> diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h >>> index 35a5abcc4ca3..9f0710ab4292 100644 >>> --- a/include/kvm/arm_hypercalls.h >>> +++ b/include/kvm/arm_hypercalls.h >>> @@ -7,6 +7,7 @@ >>> #include >>> >>> int kvm_hvc_call_handler(struct kvm_vcpu *vcpu); >>> +int kvm_update_stolen_time(struct kvm_vcpu *vcpu); >>> >>> static inline u32 smccc_get_function(struct kvm_vcpu *vcpu) >>> { >>> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h >>> index bde5374ae021..1c88e69db3d9 100644 >>> --- a/include/linux/kvm_types.h >>> +++ b/include/linux/kvm_types.h >>> @@ -35,6 +35,8 @@ typedef unsigned long gva_t; >>> typedef u64 gpa_t; >>> typedef u64 gfn_t; >>> >>> +#define GPA_INVALID (~(gpa_t)0) >>> + >>> typedef unsigned long hva_t; >>> typedef u64 hpa_t; >>> typedef u64 hfn_t; >>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c >>> index f645c0fbf7ec..ebd963d2580b 100644 >>> --- a/virt/kvm/arm/arm.c >>> +++ b/virt/kvm/arm/arm.c >>> @@ -40,6 +40,10 @@ >>> #include >>> #include >>> >>> +#include >>> +#include >>> +#include >>> + >>> #ifdef REQUIRES_VIRT >>> __asm__(".arch_extension virt"); >>> #endif >>> @@ -135,6 +139,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) >>> kvm->arch.max_vcpus = vgic_present ? >>> kvm_vgic_get_max_vcpus() : KVM_MAX_VCPUS; >>> >>> + kvm->arch.pvtime.st_base = GPA_INVALID; >>> return ret; >>> out_free_stage2_pgd: >>> kvm_free_stage2_pgd(kvm); >>> @@ -371,6 +376,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) >>> kvm_vcpu_load_sysregs(vcpu); >>> kvm_arch_vcpu_load_fp(vcpu); >>> kvm_vcpu_pmu_restore_guest(vcpu); >>> + kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu); >>> >>> if (single_task_running()) >>> vcpu_clear_wfe_traps(vcpu); >>> @@ -617,6 +623,15 @@ static void vcpu_req_sleep(struct kvm_vcpu *vcpu) >>> smp_rmb(); >>> } >>> >>> +static void vcpu_req_record_steal(struct kvm_vcpu *vcpu) >>> +{ >>> + int idx; >>> + >>> + idx = srcu_read_lock(&vcpu->kvm->srcu); >>> + kvm_update_stolen_time(vcpu); >>> + srcu_read_unlock(&vcpu->kvm->srcu, idx); >>> +} >>> + >>> static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu) >>> { >>> return vcpu->arch.target >= 0; >>> @@ -636,6 +651,9 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu) >>> * that a VCPU sees new virtual interrupts. >>> */ >>> kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu); >>> + >>> + if (kvm_check_request(KVM_REQ_RECORD_STEAL, vcpu)) >>> + vcpu_req_record_steal(vcpu); >> >> Something troubles me. Here, you've set the request on load. But you >> can be preempted at any time (preemption gets disabled just after). >> >> I have the feeling that should you get preempted right here, you'll >> end-up having accumulated the wrong amount of steal time, as the >> request put via load when you'll get scheduled back in will only get >> processed after a full round of entry/exit/entry, which doesn't look >> great. > > Ah, no. We're saved by the check for pending requests right before we > jump in the guest, causing an early exit and the whole shebang to be > restarted. Yes, that's my understanding. Obviously not ideal if it happens in that small window, but everything is redone to get the right values in the end. Steve