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

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Message-ID: <20170830200458.GK24522@cbox>
Date:   Wed, 30 Aug 2017 22:04:58 +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 Wed, Aug 30, 2017 at 03:08:01PM +0100, Marc Zyngier wrote:
> On 28/08/17 19:18, Christoffer Dall wrote:
> > 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?
> I believe we should be OK here, as we hold the ITS mutex during any
> command processing, and both the forward/unforward paths take that same
> mutex.

ok, yes, as long as the only other modifirs are the forward/unforward
paths and they hold the mutex, we should be fine.

> 
> On a slightly different note, it looks like the MOVI code could benefit
> from using vgic_its_resolve_lpi(), which has been introduce earlier in
> this series.

Only problem is you'd need to get a handle to the ite as well to change
the collection pointer.  I suppose you could add another pointer
pointer.

-Christoffer