linux-kernel - Re: [PATCH v3 44/59] KVM: arm/arm64: GICv4: Handle MOVI applied to a VLPI

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Date:   Mon, 28 Aug 2017 20:18:17 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Eric Auger <eric.auger@...hat.com>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v3 44/59] KVM: arm/arm64: GICv4: Handle MOVI applied to a
 VLPI

On Mon, Jul 31, 2017 at 06:26:22PM +0100, Marc Zyngier wrote:
> When the guest issues a MOVI, we need to tell the physical ITS
> that we're now targetting a new vcpu. This is done by extracting
> the current mapping, updating the target, and reapplying the
> mapping. The core ITS code should do the right thing.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 79bac93d3e7d..aaad577ce328 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -706,6 +706,19 @@ static int vgic_its_cmd_handle_movi(struct kvm *kvm, struct vgic_its *its,
>  	ite->irq->target_vcpu = vcpu;
>  	spin_unlock(&ite->irq->irq_lock);
>  
> +	if (ite->irq->hw) {
> +		struct its_vlpi_map map;
> +		int ret;
> +
> +		ret = its_get_vlpi(ite->irq->host_irq, &map);
> +		if (ret)
> +			return ret;
> +
> +		map.vpe_idx = vcpu->vcpu_id;
> +
> +		return its_map_vlpi(ite->irq->host_irq, &map);

Since you're not holding the irq_lock across these two calls, would it
be possible that the forwarding was removed through some other call path
here, and could you end up passing an invalid host_irq to its_map_vlpi?

Thanks,
-Christoffer

> +	}
> +
>  	return 0;
>  }
>  
> -- 
> 2.11.0
>