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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3BE4C433EF for ; Tue, 11 Jan 2022 17:56:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345051AbiAKR4Y (ORCPT ); Tue, 11 Jan 2022 12:56:24 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:53998 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345055AbiAKRzY (ORCPT ); Tue, 11 Jan 2022 12:55:24 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A0B8561747; Tue, 11 Jan 2022 17:55:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0446CC36AE3; Tue, 11 Jan 2022 17:55:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1641923723; bh=RVygJsEvssP8P2RLr8QBntsWiyJZVe5Z/MKKlT2crFs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=vFwORGSKM8ks3VasGLSqIDIZTlWdmAlZYTgPPWXyAp1b0yRkRrzlyG1VF9zMaWXIH MCIUILIux34Uol1hrouHg4Jiidd2tvzwWWgoFQNhdargIRaM/IH0Izlrr0gLNrfNz5 0qAkx42Ycd7KaQg2IcBCD/oAQLLkrWQKuPNuNzLPjlXwbDqTBwE04Zg/cK0y2XtFqx lj3HtfBvuXSjE0AmvoK21oMYGES0xEUbfuPZJ2MXYUTJkUpmZVME3+tCC3fc6bOtH9 LXsiwx7IKimIBJY/BLgv8AKpoRlJkz2w6dnW4KmX1IdKxFDMS32hHaPQzMP6xPIC1X tG+APh78riWjQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1n7LMf-00HSbo-4W; Tue, 11 Jan 2022 17:55:21 +0000 Date: Tue, 11 Jan 2022 17:55:20 +0000 Message-ID: <87tuearwc7.wl-maz@kernel.org> From: Marc Zyngier To: Mark Rutland Cc: linux-kernel@vger.kernel.org, aleksandar.qemu.devel@gmail.com, alexandru.elisei@arm.com, anup.patel@wdc.com, aou@eecs.berkeley.edu, atish.patra@wdc.com, benh@kernel.crashing.org, borntraeger@linux.ibm.com, bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org, dave.hansen@linux.intel.com, david@redhat.com, frankja@linux.ibm.com, frederic@kernel.org, gor@linux.ibm.com, hca@linux.ibm.com, imbrenda@linux.ibm.com, james.morse@arm.com, jmattson@google.com, joro@8bytes.org, kvm@vger.kernel.org, mingo@redhat.com, mpe@ellerman.id.au, nsaenzju@redhat.com, palmer@dabbelt.com, paulmck@kernel.org, paulus@samba.org, paul.walmsley@sifive.com, pbonzini@redhat.com, seanjc@google.com, suzuki.poulose@arm.com, tglx@linutronix.de, tsbogend@alpha.franken.de, vkuznets@redhat.com, wanpengli@tencent.com, will@kernel.org Subject: Re: [PATCH 2/5] kvm/arm64: rework guest entry logic In-Reply-To: <20220111153539.2532246-3-mark.rutland@arm.com> References: <20220111153539.2532246-1-mark.rutland@arm.com> <20220111153539.2532246-3-mark.rutland@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: mark.rutland@arm.com, linux-kernel@vger.kernel.org, aleksandar.qemu.devel@gmail.com, alexandru.elisei@arm.com, anup.patel@wdc.com, aou@eecs.berkeley.edu, atish.patra@wdc.com, benh@kernel.crashing.org, borntraeger@linux.ibm.com, bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org, dave.hansen@linux.intel.com, david@redhat.com, frankja@linux.ibm.com, frederic@kernel.org, gor@linux.ibm.com, hca@linux.ibm.com, imbrenda@linux.ibm.com, james.morse@arm.com, jmattson@google.com, joro@8bytes.org, kvm@vger.kernel.org, mingo@redhat.com, mpe@ellerman.id.au, nsaenzju@redhat.com, palmer@dabbelt.com, paulmck@kernel.org, paulus@samba.org, paul.walmsley@sifive.com, pbonzini@redhat.com, seanjc@google.com, suzuki.poulose@arm.com, tglx@linutronix.de, tsbogend@alpha.franken.de, vkuznets@redhat.com, wanpengli@tencent.com, will@kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 11 Jan 2022 15:35:36 +0000, Mark Rutland wrote: > > In kvm_arch_vcpu_ioctl_run() we enter an RCU extended quiescent state > (EQS) by calling guest_enter_irqoff(), and unmasked IRQs prior to > exiting the EQS by calling guest_exit(). As the IRQ entry code will not > wake RCU in this case, we may run the core IRQ code and IRQ handler > without RCU watching, leading to various potential problems. > > Additionally, we do not inform lockdep or tracing that interrupts will > be enabled during guest execution, which caan lead to misleading traces > and warnings that interrupts have been enabled for overly-long periods. > > This patch fixes these issues by using the new timing and context > entry/exit helpers to ensure that interrupts are handled during guest > vtime but with RCU watching, with a sequence: > > guest_timing_enter_irqoff(); > > exit_to_guest_mode(); > < run the vcpu > > enter_from_guest_mode(); > > < take any pending IRQs > > > guest_timing_exit_irqoff(); > > Since instrumentation may make use of RCU, we must also ensure that no > instrumented code is run during the EQS. I've split out the critical > section into a new kvm_arm_enter_exit_vcpu() helper which is marked > noinstr. > > Fixes: 1b3d546daf85ed2b ("arm/arm64: KVM: Properly account for guest CPU time") > Reported-by: Nicolas Saenz Julienne > Signed-off-by: Mark Rutland > Cc: Alexandru Elisei > Cc: Catalin Marinas > Cc: Frederic Weisbecker > Cc: James Morse > Cc: Marc Zyngier > Cc: Paolo Bonzini > Cc: Paul E. McKenney > Cc: Suzuki K Poulose > Cc: Will Deacon > --- > arch/arm64/kvm/arm.c | 51 ++++++++++++++++++++++++++++---------------- > 1 file changed, 33 insertions(+), 18 deletions(-) > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index e4727dc771bf..1721df2522c8 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -764,6 +764,24 @@ static bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu, int *ret) > xfer_to_guest_mode_work_pending(); > } > > +/* > + * Actually run the vCPU, entering an RCU extended quiescent state (EQS) while > + * the vCPU is running. > + * > + * This must be noinstr as instrumentation may make use of RCU, and this is not > + * safe during the EQS. > + */ > +static int noinstr kvm_arm_vcpu_enter_exit(struct kvm_vcpu *vcpu) > +{ > + int ret; > + > + exit_to_guest_mode(); > + ret = kvm_call_hyp_ret(__kvm_vcpu_run, vcpu); > + enter_from_guest_mode(); > + > + return ret; > +} > + > /** > * kvm_arch_vcpu_ioctl_run - the main VCPU run function to execute guest code > * @vcpu: The VCPU pointer > @@ -854,9 +872,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) > * Enter the guest > */ > trace_kvm_entry(*vcpu_pc(vcpu)); > - guest_enter_irqoff(); > + guest_timing_enter_irqoff(); > > - ret = kvm_call_hyp_ret(__kvm_vcpu_run, vcpu); > + ret = kvm_arm_vcpu_enter_exit(vcpu); > > vcpu->mode = OUTSIDE_GUEST_MODE; > vcpu->stat.exits++; > @@ -891,26 +909,23 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) > kvm_arch_vcpu_ctxsync_fp(vcpu); > > /* > - * We may have taken a host interrupt in HYP mode (ie > - * while executing the guest). This interrupt is still > - * pending, as we haven't serviced it yet! > + * We must ensure that any pending interrupts are taken before > + * we exit guest timing so that timer ticks are accounted as > + * guest time. Transiently unmask interrupts so that any > + * pending interrupts are taken. > * > - * We're now back in SVC mode, with interrupts > - * disabled. Enabling the interrupts now will have > - * the effect of taking the interrupt again, in SVC > - * mode this time. > + * Per ARM DDI 0487G.b section D1.13.4, an ISB (or other > + * context synchronization event) is necessary to ensure that > + * pending interrupts are taken. > */ > local_irq_enable(); > + isb(); > + local_irq_disable(); Small nit: we may be able to elide this enable/isb/disable dance if a read of ISR_EL1 returns 0. > + > + guest_timing_exit_irqoff(); > + > + local_irq_enable(); > > - /* > - * We do local_irq_enable() before calling guest_exit() so > - * that if a timer interrupt hits while running the guest we > - * account that tick as being spent in the guest. We enable > - * preemption after calling guest_exit() so that if we get > - * preempted we make sure ticks after that is not counted as > - * guest time. > - */ > - guest_exit(); > trace_kvm_exit(ret, kvm_vcpu_trap_get_class(vcpu), *vcpu_pc(vcpu)); > > /* Exit types that need handling before we can be preempted */ Reviewed-by: Marc Zyngier M. -- Without deviation from the norm, progress is not possible.