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=-6.0 required=5.0 tests=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 C1DD77D2F0 for ; Sat, 3 Aug 2019 17:58:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728370AbfHCR6a (ORCPT ); Sat, 3 Aug 2019 13:58:30 -0400 Received: from inca-roads.misterjones.org ([213.251.177.50]:58512 "EHLO inca-roads.misterjones.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726403AbfHCR6a (ORCPT ); Sat, 3 Aug 2019 13:58:30 -0400 Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why) by cheepnis.misterjones.org with esmtpsa (TLSv1.2:AES256-GCM-SHA384:256) (Exim 4.80) (envelope-from ) id 1htyIO-00025f-BD; Sat, 03 Aug 2019 19:58:20 +0200 Date: Sat, 3 Aug 2019 18:58:17 +0100 From: Marc Zyngier To: Steven Price Cc: Catalin Marinas , Paolo Bonzini , Radim =?UTF-8?B?S3LEjW3DocWZ?= , 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: Re: [PATCH 4/9] KVM: arm64: Support stolen time reporting via shared structure Message-ID: <20190803185817.11285b2a@why> In-Reply-To: <20190802145017.42543-5-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-5-steven.price@arm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, 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 X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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. Am I getting it right? M. -- Without deviation from the norm, progress is not possible.