linux-kernel - Re: [PATCH v2 0/3] KVM: Properly account for guest CPU time

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Message-ID: <76aa7dcc-ba57-f12d-bf19-880fa71f429f@de.ibm.com>
Date:   Tue, 13 Apr 2021 10:32:59 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Tokarev <mjt@....msk.ru>
Subject: Re: [PATCH v2 0/3] KVM: Properly account for guest CPU time



On 13.04.21 09:16, Wanpeng Li wrote:
> The bugzilla https://bugzilla.kernel.org/show_bug.cgi?id=209831
> reported that the guest time remains 0 when running a while true
> loop in the guest.
> 
> The commit 87fa7f3e98a131 ("x86/kvm: Move context tracking where it
> belongs") moves guest_exit_irqoff() close to vmexit breaks the
> tick-based time accouting when the ticks that happen after IRQs are
> disabled are incorrectly accounted to the host/system time. This is
> because we exit the guest state too early.
> 
> This patchset splits both context tracking logic and the time accounting
> logic from guest_enter/exit_irqoff(), keep context tracking around the
> actual vmentry/exit code, have the virt time specific helpers which
> can be placed at the proper spots in kvm. In addition, it will not
> break the world outside of x86.
> 
> v1 -> v2:
>   * split context_tracking from guest_enter/exit_irqoff
>   * provide separate vtime accounting functions for consistent
>   * place the virt time specific helpers at the proper splot
> 
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Michael Tokarev <mjt@....msk.ru>
> 
> Wanpeng Li (3):
>    context_tracking: Split guest_enter/exit_irqoff
>    context_tracking: Provide separate vtime accounting functions
>    x86/kvm: Fix vtime accounting
> 
>   arch/x86/kvm/svm/svm.c           |  6 ++-
>   arch/x86/kvm/vmx/vmx.c           |  6 ++-
>   arch/x86/kvm/x86.c               |  1 +
>   include/linux/context_tracking.h | 84 +++++++++++++++++++++++++++++++---------
>   4 files changed, 74 insertions(+), 23 deletions(-)
> 

The non CONFIG_VIRT_CPU_ACCOUNTING_GEN look good.