Re: [PATCH v3 1/6] KVM: Don't use KVM_REQ_PENDING_TIMER

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jul 09, 2012 at 08:05:40PM +0300, Avi Kivity wrote:
> It's a write-only bit, set by the timer and cleared by the main loop.
> Remove it.  Retain the definition since ppc uses it.
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>
> ---
>  arch/x86/kvm/timer.c | 8 ++------
>  arch/x86/kvm/x86.c   | 1 -
>  2 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/timer.c b/arch/x86/kvm/timer.c
> index 6b85cc6..c28f838 100644
> --- a/arch/x86/kvm/timer.c
> +++ b/arch/x86/kvm/timer.c
> @@ -27,14 +27,10 @@ enum hrtimer_restart kvm_timer_fn(struct hrtimer *data)
>  	/*
>  	 * There is a race window between reading and incrementing, but we do
>  	 * not care about potentially losing timer events in the !reinject
> -	 * case anyway. Note: KVM_REQ_PENDING_TIMER is implicitly checked
> -	 * in vcpu_enter_guest.
So what about the part that says "KVM_REQ_PENDING_TIMER is implicitly
checked in vcpu_enter_guest"? This patch drops the check. So now if
timer triggers while vcpu is in userspace it will enter guest mode
without injecting timer interrupt on the next ioctl(KVM_RUN). Or do I
miss something here?

> +	 * case anyway.
>  	 */
> -	if (ktimer->reinject || !atomic_read(&ktimer->pending)) {
> +	if (ktimer->reinject || !atomic_read(&ktimer->pending))
>  		atomic_inc(&ktimer->pending);
> -		/* FIXME: this code should not know anything about vcpus */
> -		kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> -	}
>  
>  	if (waitqueue_active(q))
>  		wake_up_interruptible(q);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ff0b487..ae07ef2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5437,7 +5437,6 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
>  		if (r <= 0)
>  			break;
>  
> -		clear_bit(KVM_REQ_PENDING_TIMER, &vcpu->requests);
>  		if (kvm_cpu_has_pending_timer(vcpu))
>  			kvm_inject_pending_timer_irqs(vcpu);
>  
> -- 
> 1.7.11
> 
> --
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--
			Gleb.