linux-kernel - Re: [RFC 25/55] KVM: arm/arm64: Let vcpu thread modify its own active state

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Date:   Wed, 22 Feb 2017 13:27:14 +0100
From:   Christoffer Dall <cdall@...aro.org>
To:     Jintack Lim <jintack@...columbia.edu>
Cc:     christoffer.dall@...aro.org, marc.zyngier@....com,
        pbonzini@...hat.com, rkrcmar@...hat.com, linux@...linux.org.uk,
        catalin.marinas@....com, will.deacon@....com,
        vladimir.murzin@....com, suzuki.poulose@....com,
        mark.rutland@....com, james.morse@....com,
        lorenzo.pieralisi@....com, kevin.brodsky@....com,
        wcohen@...hat.com, shankerd@...eaurora.org, geoff@...radead.org,
        andre.przywara@....com, eric.auger@...hat.com,
        anna-maria@...utronix.de, shihwei@...columbia.edu,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 25/55] KVM: arm/arm64: Let vcpu thread modify its own
 active state

On Mon, Jan 09, 2017 at 01:24:21AM -0500, Jintack Lim wrote:
> Currently, if a vcpu thread tries to change its own active state when
> the irq is already in AP list, it'll loop forever. Since the VCPU thread
> has already synced back LR state to the struct vgic_irq, let it modify
> its own state safely.
> 
> Signed-off-by: Jintack Lim <jintack@...columbia.edu>
> ---
>  virt/kvm/arm/vgic/vgic-mmio.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c
> index ebe1b9f..049c570 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio.c
> @@ -192,9 +192,9 @@ static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq,
>  	 * If this virtual IRQ was written into a list register, we
>  	 * have to make sure the CPU that runs the VCPU thread has
>  	 * synced back LR state to the struct vgic_irq.  We can only
> -	 * know this for sure, when either this irq is not assigned to
> +	 * know this for sure, when this irq is not assigned to
>  	 * anyone's AP list anymore, or the VCPU thread is not
> -	 * running on any CPUs.
> +	 * running on any CPUs, or current thread is the VCPU thread.
>  	 *
>  	 * In the opposite case, we know the VCPU thread may be on its
>  	 * way back from the guest and still has to sync back this
> @@ -202,6 +202,7 @@ static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq,
>  	 * other thread sync back the IRQ.
>  	 */
>  	while (irq->vcpu && /* IRQ may have state in an LR somewhere */
> +	       irq->vcpu != vcpu && /* Current thread is not the VCPU thread */
>  	       irq->vcpu->cpu != -1) /* VCPU thread is running */
>  		cond_resched_lock(&irq->irq_lock);
>  
> -- 
> 1.9.1
> 
> 

This seems to be an independent fix, so please send it outside of this
series as an individual patch.

Thanks,
-Christoffer