From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PATCH v3 03/24] KVM: x86: check against irqchip_mode in
 kvm_set_routing_entry()
Date: Wed, 12 Apr 2017 20:36:55 +0200
Message-ID: <20170412183655.GB20145@potion>
References: <20170407085041.5257-1-david@redhat.com>
 <20170407085041.5257-4-david@redhat.com>
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Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
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2017-04-07 10:50+0200, David Hildenbrand:
> Let's replace the checks for pic_in_kernel() and ioapic_in_kernel() by
> checks against irqchip_mode.
> 
> Also make sure that creation of any route is only possible if we have
> an lapic in kernel (irqchip_in_kernel()) or if we are currently
> inititalizing the irqchip.
> 
> This is necessary to switch pic_in_kernel() and ioapic_in_kernel() to
> irqchip_mode, too.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  arch/x86/kvm/irq_comm.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index 6825cd3..2e5eec8 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -282,24 +282,26 @@ int kvm_set_routing_entry(struct kvm *kvm,
>  	int delta;
>  	unsigned max_pin;
>  
> +	/* also allow creation of routes during KVM_IRQCHIP_INIT_IN_PROGRESS */
> +	if (kvm->arch.irqchip_mode == KVM_IRQCHIP_NONE)
> +		goto out;
> +
> +	/* Matches smp_wmb() when setting irqchip_mode */
> +	smp_rmb();

This barrier is superfluous as well ... aren't all callers using
kvm->lock to provide ordering?

The check for KVM_IRQCHIP_NONE would prevent nothing if we could catch
the initialization from the outside and hence need a barrier.

Thanks.