Subject: [PATCH 08/10] KVM: arm-vgic: Support unqueueing of LRs to the dist

From: [email-masked] (Christoffer Dall)
Date: Mon, 16 Dec 2013 09:07:57 -0800

On Mon, Dec 16, 2013 at 12:53:37PM +0000, Marc Zyngier wrote:
> On 12/12/13 19:55, Christoffer Dall wrote:
> > To properly access the VGIC state from user space it is very unpractical
> > to have to loop through all the LRs in all register access functions.
> > Instead, support moving all pending state from LRs to the distributor,
> > but leave active state LRs alone.
> > 
> > Note that to accurately present the active and pending state to VCPUs
> > reading these distributor registers from a live VM, we would have to
> > stop all other VPUs than the calling VCPU and ask each CPU to unqueue
> > their LR state onto the distributor and add fields to track active state
> > on the distributor side as well.  We don't have any users of such
> > functionality yet and there are other inaccuracies of the GIC emulation,
> > so don't provide accurate synchronized access to this state just yet.
> > However, when the time comes, having this function should help.
> > 
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > ---
> > Changelog[v4]:
> >  - Reworked vgic_unqueue_irqs to explicitly check for the active bit and
> >    to not use __test_and_clear_bit.
> > 
> > Changelog[v3]:
> >  - New patch in series
> > 
> >  virt/kvm/arm/vgic.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 81 insertions(+), 5 deletions(-)
> > 
> > diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> > index 88599b5..8067e76 100644
> > --- a/virt/kvm/arm/vgic.c
> > +++ b/virt/kvm/arm/vgic.c
> > @@ -589,6 +589,78 @@ static bool handle_mmio_sgi_reg(struct kvm_vcpu *vcpu,
> >  	return false;
> >  }
> >  
> > +#define LR_CPUID(lr)	\
> > +	(((lr) & GICH_LR_PHYSID_CPUID) >> GICH_LR_PHYSID_CPUID_SHIFT)
> > +#define LR_IRQID(lr)	\
> > +	((lr) & GICH_LR_VIRTUALID)
> > +
> > +static void vgic_retire_lr(int lr_nr, int irq, struct vgic_cpu *vgic_cpu)
> > +{
> > +	clear_bit(lr_nr, vgic_cpu->lr_used);
> > +	vgic_cpu->vgic_lr[lr_nr] &= ~GICH_LR_STATE;
> > +	vgic_cpu->vgic_irq_lr_map[irq] = LR_EMPTY;
> > +}
> > +
> > +/**
> > + * vgic_unqueue_irqs - move pending IRQs from LRs to the distributor
> > + * @vgic_cpu: Pointer to the vgic_cpu struct holding the LRs
> > + *
> > + * Move any pending IRQs that have already been assigned to LRs back to the
> > + * emulated distributor state so that the complete emulated state can be read
> > + * from the main emulation structures without investigating the LRs.
> > + *
> > + * Note that IRQs in the active state in the LRs get their pending state moved
> > + * to the distributor but the active state stays in the LRs, because we don't
> > + * track the active state on the distributor side.
> > + */
> > +static void vgic_unqueue_irqs(struct kvm_vcpu *vcpu)
> > +{
> > +	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> > +	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> > +	int vcpu_id = vcpu->vcpu_id;
> > +	int i, irq, source_cpu;
> > +	u32 *lr;
> > +
> > +	for_each_set_bit(i, vgic_cpu->lr_used, vgic_cpu->nr_lr) {
> > +		lr = &vgic_cpu->vgic_lr[i];
> > +		irq = LR_IRQID(*lr);
> > +		source_cpu = LR_CPUID(*lr);
> > +
> > +		/*
> > +		 * There are three options for the state bits:
> > +		 *
> > +		 * 01: pending
> > +		 * 10: active
> > +		 * 11: pending and active
> > +		 *
> > +		 * If the LR holds only an active interrupt (not pending) then
> > +		 * just leave it alone.
> > +		 */
> > +		if ((*lr & GICH_LR_STATE) == GICH_LR_ACTIVE_BIT)
> > +			continue;
> > +
> > +		/*
> > +		 * If the interrupt was only pending (not "active" or "pending
> > +		 * and active") then we the pending state will get moved to
>                                      ^^ extra 'we'
> > +		 * the distributor and the LR does not hold any info and can
> > +		 * be marked as free for other use.
> > +		 */
> > +		if ((*lr & GICH_LR_STATE) == GICH_LR_PENDING_BIT)
> > +			vgic_retire_lr(i, irq, vgic_cpu);
> 
> We should handle the ACTIVE+PENDING case, and I don't think we do.
> Should it be (*lr & GICH_LR_PENDING_BIT)? I think the previous version
> handled this case correctly.
> 

nice catch!  We just need to always clear the pending bit on the LR.
I'll fix that in a re-spin.

-Christoffer

> > +		/*
> > +		 * Finally, reestablish the pending state on the distributor
> > +		 * and the CPU interface.  It may have already been pending,
> > +		 * but that is fine, then we are only setting a few bits that
> > +		 * were already set.
> > +		 */
> > +		vgic_dist_irq_set(vcpu, irq);
> > +		if (irq < VGIC_NR_SGIS)
> > +			dist->irq_sgi_sources[vcpu_id][irq] |= 1 << source_cpu;
> > +		vgic_update_state(vcpu->kvm);
> > +	}
> > +}
> > +
> >  static bool handle_mmio_sgi_clear(struct kvm_vcpu *vcpu,
> >  				  struct kvm_exit_mmio *mmio,
> >  				  phys_addr_t offset)
> > @@ -848,8 +920,6 @@ static void vgic_update_state(struct kvm *kvm)
> >  	}
> >  }
> >  
> > -#define LR_CPUID(lr)	\
> > -	(((lr) & GICH_LR_PHYSID_CPUID) >> GICH_LR_PHYSID_CPUID_SHIFT)
> >  #define MK_LR_PEND(src, irq)	\
> >  	(GICH_LR_PENDING_BIT | ((src) << GICH_LR_PHYSID_CPUID_SHIFT) | (irq))
> >  
> > @@ -871,9 +941,7 @@ static void vgic_retire_disabled_irqs(struct kvm_vcpu *vcpu)
> >  		int irq = vgic_cpu->vgic_lr[lr] & GICH_LR_VIRTUALID;
> >  
> >  		if (!vgic_irq_is_enabled(vcpu, irq)) {
> > -			vgic_cpu->vgic_irq_lr_map[irq] = LR_EMPTY;
> > -			clear_bit(lr, vgic_cpu->lr_used);
> > -			vgic_cpu->vgic_lr[lr] &= ~GICH_LR_STATE;
> > +			vgic_retire_lr(lr, irq, vgic_cpu);
> >  			if (vgic_irq_is_active(vcpu, irq))
> >  				vgic_irq_clear_active(vcpu, irq);
> >  		}
> > @@ -1675,6 +1743,14 @@ static int vgic_attr_regs_access(struct kvm_device *dev,
> >  		}
> >  	}
> >  
> > +	/*
> > +	 * Move all pending IRQs from the LRs on all VCPUs so the pending
> > +	 * state can be properly represented in the register state accessible
> > +	 * through this API.
> > +	 */
> > +	kvm_for_each_vcpu(c, tmp_vcpu, dev->kvm)
> > +		vgic_unqueue_irqs(tmp_vcpu);
> > +
> >  	offset -= r->base;
> >  	r->handle_mmio(vcpu, &mmio, offset);
> >  
> > 
> 
> 
> -- 
> Jazz is not dead. It just smells funny...
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-- 
Christoffer