linux-kernel - Re: [PATCH 3/4] KVM: i8254: remove unnecessary irqchip_in

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Message-ID: <20150730043645.GF15229@google.com>
Date:	Wed, 29 Jul 2015 21:36:45 -0700
From:	Steve Rutherford <srutherford@...gle.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	mtosatti@...hat.com, rkrcmar@...hat.com
Subject: Re: [PATCH 3/4] KVM: i8254: remove unnecessary irqchip_in_kernel
 check

On Wed, Jul 29, 2015 at 03:28:57PM +0200, Paolo Bonzini wrote:
> The PIT is only created if irqchip_in_kernel returns true, so the
> check is superfluous.
I poked around. Looks to me like the existence of an IOAPIC is not
checked on the creation of the in-kernel PIT. Userspace might limit itself to
that scenario (PIT implies IOAPIC in-kernel), but that isn't enforced at PIT
creation.

It's worth adding that check in.

> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/i8254.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> index f90952f64e79..f588eb7bdf45 100644
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -333,7 +333,7 @@ static void create_pit_timer(struct kvm *kvm, u32 val, int is_period)
>  	struct kvm_kpit_state *ps = &kvm->arch.vpit->pit_state;
>  	s64 interval;
>  
> -	if (!irqchip_in_kernel(kvm) || ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)
> +	if (ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)
>  		return;
>  
>  	interval = muldiv64(val, NSEC_PER_SEC, KVM_PIT_FREQ);
> -- 
> 1.8.3.1
> 
> 
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