Re: [PATCH v2 11/17] arm64: KVM: vgic-v2: Only wipe LRs on vcpu exit

[Marc Zyngier <marc.zyngier@arm.com>]

On Thu, 3 Mar 2016 00:08:19 +0100
Christoffer Dall <christoffer.dall@linaro.org> wrote:

> On Wed, Feb 17, 2016 at 04:40:43PM +0000, Marc Zyngier wrote:
> > So far, we're always writing all possible LRs, setting the empty
> > ones with a zero value. This is obvious doing a low of work for
> 
> s/low/lot/
> 
> > nothing, and we're better off clearing those we've actually
> > dirtied on the exit path (it is very rare to inject more than one
> > interrupt at a time anyway).
> > 
> > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> > ---
> >  arch/arm64/kvm/hyp/vgic-v2-sr.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/vgic-v2-sr.c b/arch/arm64/kvm/hyp/vgic-v2-sr.c
> > index 3dbbc6b..e53f131 100644
> > --- a/arch/arm64/kvm/hyp/vgic-v2-sr.c
> > +++ b/arch/arm64/kvm/hyp/vgic-v2-sr.c
> > @@ -101,6 +101,7 @@ static void __hyp_text save_lrs(struct kvm_vcpu *vcpu, void __iomem *base)
> >  		}
> >  
> >  		cpu_if->vgic_lr[i] = readl_relaxed(base + GICH_LR0 + (i * 4));
> > +		writel_relaxed(0, base + GICH_LR0 + (i * 4));
> >  	}
> >  }
> >  
> > @@ -158,12 +159,11 @@ void __hyp_text __vgic_v2_restore_state(struct kvm_vcpu *vcpu)
> >  		writel_relaxed(cpu_if->vgic_hcr, base + GICH_HCR);
> >  		writel_relaxed(cpu_if->vgic_apr, base + GICH_APR);
> >  		for (i = 0; i < nr_lr; i++) {
> > -			u32 val = 0;
> > -
> > -			if (live_lrs & (1UL << i))
> > -				val = cpu_if->vgic_lr[i];
> > +			if (!(live_lrs & (1UL << i)))
> > +				continue;
> 
> how can we be sure that the LRs are clear when we launch our first VM on
> a given physical CPU?  Don't we need to flush the LRs during VGIC init
> time?

Very good point. The registers reset to zero, but there is indeed no
guarantee that we don't get something clobbered by EL3, or some earlier
crash.

I'll add a patch to that effect.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.