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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83709C433F5 for ; Fri, 8 Oct 2021 05:54:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 67F7460F94 for ; Fri, 8 Oct 2021 05:54:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231419AbhJHFz7 convert rfc822-to-8bit (ORCPT ); Fri, 8 Oct 2021 01:55:59 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:49253 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229721AbhJHFz6 (ORCPT ); Fri, 8 Oct 2021 01:55:58 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-406-Z3P4acovOzaCeubDXSg87A-1; Fri, 08 Oct 2021 01:53:49 -0400 X-MC-Unique: Z3P4acovOzaCeubDXSg87A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 545D083DBC0; Fri, 8 Oct 2021 05:53:47 +0000 (UTC) Received: from bahia.huguette (unknown [10.39.192.158]) by smtp.corp.redhat.com (Postfix) with ESMTP id 81691196E2; Fri, 8 Oct 2021 05:53:42 +0000 (UTC) Date: Fri, 8 Oct 2021 07:53:41 +0200 From: Greg Kurz To: Laurent Vivier Cc: kvm-ppc@vger.kernel.org, Paul Mackerras , Benjamin Herrenschmidt , Michael Ellerman , linux-kernel@vger.kernel.org, Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, stable@vger.kernel.org Subject: Re: [PATCH v2] KVM: PPC: Defer vtime accounting 'til after IRQ handling Message-ID: <20211008074438.49fc577a@bahia.huguette> In-Reply-To: <20211007142856.41205-1-lvivier@redhat.com> References: <20211007142856.41205-1-lvivier@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=groug@kaod.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kaod.org Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Thu, 7 Oct 2021 16:28:56 +0200 Laurent Vivier wrote: > Commit 112665286d08 moved guest_exit() in the interrupt protected > area to avoid wrong context warning (or worse), but the tick counter > cannot be updated and the guest time is accounted to the system time. > > To fix the problem port to POWER the x86 fix > 160457140187 ("Defer vtime accounting 'til after IRQ handling"): > > "Defer the call to account guest time until after servicing any IRQ(s) > that happened in the guest or immediately after VM-Exit. Tick-based > accounting of vCPU time relies on PF_VCPU being set when the tick IRQ > handler runs, and IRQs are blocked throughout the main sequence of > vcpu_enter_guest(), including the call into vendor code to actually > enter and exit the guest." > > Fixes: 112665286d08 ("KVM: PPC: Book3S HV: Context tracking exit guest context before enabling irqs") > Cc: npiggin@gmail.com > Cc: # 5.12 > Signed-off-by: Laurent Vivier > --- > > Notes: > v2: remove reference to commit 61bd0f66ff92 > cc stable 5.12 > add the same comment in the code as for x86 > Works for me. As you stated in your answer, someone can polish the code later on. Reviewed-by: Greg Kurz > arch/powerpc/kvm/book3s_hv.c | 24 ++++++++++++++++++++---- > 1 file changed, 20 insertions(+), 4 deletions(-) > > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > index 2acb1c96cfaf..a694d1a8f6ce 100644 > --- a/arch/powerpc/kvm/book3s_hv.c > +++ b/arch/powerpc/kvm/book3s_hv.c > @@ -3695,6 +3695,8 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc) > > srcu_read_unlock(&vc->kvm->srcu, srcu_idx); > > + context_tracking_guest_exit(); > + > set_irq_happened(trap); > > spin_lock(&vc->lock); > @@ -3726,9 +3728,15 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc) > > kvmppc_set_host_core(pcpu); > > - guest_exit_irqoff(); > - > local_irq_enable(); > + /* > + * Wait until after servicing IRQs to account guest time so that any > + * ticks that occurred while running the guest are properly accounted > + * to the guest. Waiting until IRQs are enabled degrades the accuracy > + * of accounting via context tracking, but the loss of accuracy is > + * acceptable for all known use cases. > + */ > + vtime_account_guest_exit(); > > /* Let secondaries go back to the offline loop */ > for (i = 0; i < controlled_threads; ++i) { > @@ -4506,13 +4514,21 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit, > > srcu_read_unlock(&kvm->srcu, srcu_idx); > > + context_tracking_guest_exit(); > + > set_irq_happened(trap); > > kvmppc_set_host_core(pcpu); > > - guest_exit_irqoff(); > - > local_irq_enable(); > + /* > + * Wait until after servicing IRQs to account guest time so that any > + * ticks that occurred while running the guest are properly accounted > + * to the guest. Waiting until IRQs are enabled degrades the accuracy > + * of accounting via context tracking, but the loss of accuracy is > + * acceptable for all known use cases. > + */ > + vtime_account_guest_exit(); > > cpumask_clear_cpu(pcpu, &kvm->arch.cpu_in_guest); >