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Subject: Re: [PATCH 3/7] kvm,lapic: Justify use of swait_activate()
To: Davidlohr Bueso <dave@stgolabs.net>, mingo@kernel.org,
        peterz@infradead.org
Cc: npiggin@gmail.com, paulmck@linux.vnet.ibm.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
References: <20170913200824.28067-1-dave@stgolabs.net>
 <20170913200824.28067-4-dave@stgolabs.net>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <e2430301-6db2-b50d-a919-ed703f8db367@redhat.com>
Date: Fri, 15 Sep 2017 13:47:10 +0200
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On 13/09/2017 22:08, Davidlohr Bueso wrote:
> A comment might serve future readers.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
> ---
>  arch/x86/kvm/lapic.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index aaf10b6f5380..69c5612be786 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1324,6 +1324,10 @@ static void apic_timer_expired(struct kvm_lapic *apic)
>  	atomic_inc(&apic->lapic_timer.pending);
>  	kvm_set_pending_timer(vcpu);
>  
> +	/*
> +	 * For x86, the atomic_inc() is serialized, thus
> +	 * using swait_active() is safe.
> +	 */
>  	if (swait_active(q))
>  		swake_up(q);
>  
> 

Better add an smp_mb__after_atomic() for documentation purposes.

Paolo