linux-kernel - Re: [PATCH] Revert "KVM: x86: Unconditionally enable irqs in guest context"

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Message-ID: <CANRm+CwCqnNWr3KELG=6DLkOdWMnMP3uuyyROgXpZrPyo2A+bA@mail.gmail.com>
Date:   Tue, 19 Jan 2021 09:27:13 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        w90p710@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Revert "KVM: x86: Unconditionally enable irqs in guest context"

On Fri, 15 Jan 2021 at 11:20, Wanpeng Li <kernellwp@...il.com> wrote:
>
> On Wed, 6 Jan 2021 at 08:51, Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > +tglx
> >
> > On Tue, Jan 05, 2021, Nitesh Narayan Lal wrote:
> > > This reverts commit d7a08882a0a4b4e176691331ee3f492996579534.
> > >
> > > After the introduction of the patch:
> > >
> > >       87fa7f3e9: x86/kvm: Move context tracking where it belongs
> > >
> > > since we have moved guest_exit_irqoff closer to the VM-Exit, explicit
> > > enabling of irqs to process pending interrupts should not be required
> > > within vcpu_enter_guest anymore.
> >
> > Ugh, except that commit completely broke tick-based accounting, on both Intel
> > and AMD.  With guest_exit_irqoff() being called immediately after VM-Exit, any
> > tick that happens after IRQs are disabled will be accounted to the host.  E.g.
> > on Intel, even an IRQ VM-Exit that has already been acked by the CPU isn't
> > processed until kvm_x86_ops.handle_exit_irqoff(), well after PF_VCPU has been
> > cleared.
> >
>
> This issue can be 100% reproduced.
> https://bugzilla.kernel.org/show_bug.cgi?id=204177

Sorry, the posted link should be
https://bugzilla.kernel.org/show_bug.cgi?id=209831

    Wanpeng