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

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Date:   Wed, 6 Jan 2021 08:42:31 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Nitesh Narayan Lal <nitesh@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        seanjc@...gle.com, w90p710@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH] Revert "KVM: x86: Unconditionally enable irqs in guest context"

On Wed, 6 Jan 2021 at 06:30, Nitesh Narayan Lal <nitesh@...hat.com> 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.
>
> Conflicts:
>         arch/x86/kvm/svm.c
>
> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
> ---
>  arch/x86/kvm/svm/svm.c |  9 +++++++++
>  arch/x86/kvm/x86.c     | 11 -----------
>  2 files changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index cce0143a6f80..c9b2fbb32484 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4187,6 +4187,15 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
>
>  static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu)
>  {
> +       kvm_before_interrupt(vcpu);
> +       local_irq_enable();
> +       /*
> +        * We must have an instruction with interrupts enabled, so
> +        * the timer interrupt isn't delayed by the interrupt shadow.
> +        */
> +       asm("nop");
> +       local_irq_disable();
> +       kvm_after_interrupt(vcpu);
>  }

Why do we need to reintroduce this part?

    Wanpeng