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=-8.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 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 B5D83C433FF for ; Sat, 3 Aug 2019 18:13:34 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 52BF02087C for ; Sat, 3 Aug 2019 18:13:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 52BF02087C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id D8D004A562; Sat, 3 Aug 2019 14:13:33 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id IkNoQ-C95aaS; Sat, 3 Aug 2019 14:13:32 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 9FC514A523; Sat, 3 Aug 2019 14:13:32 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 57DDB4A51E for ; Sat, 3 Aug 2019 14:13:31 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id oKTIZo92I4hR for ; Sat, 3 Aug 2019 14:13:30 -0400 (EDT) Received: from inca-roads.misterjones.org (inca-roads.misterjones.org [213.251.177.50]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 057734A4E6 for ; Sat, 3 Aug 2019 14:13:30 -0400 (EDT) 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 1htyWw-0002Em-AQ; Sat, 03 Aug 2019 20:13:22 +0200 Date: Sat, 3 Aug 2019 19:13:19 +0100 From: Marc Zyngier To: Steven Price Subject: Re: [PATCH 4/9] KVM: arm64: Support stolen time reporting via shared structure Message-ID: <20190803191303.02e9bcc9@why> In-Reply-To: <20190803185817.11285b2a@why> References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-5-steven.price@arm.com> <20190803185817.11285b2a@why> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, kvm@vger.kernel.org, catalin.marinas@arm.com, linux-doc@vger.kernel.org, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, pbonzini@redhat.com, will@kernel.org, kvmarm@lists.cs.columbia.edu X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false 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 X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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. M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm