Re: [PATCH 2/4] KVM: arm64: vgic-v3: Implement MMIO-based LPI invalidation

[Marc Zyngier <maz@kernel.org>]

On Wed, 16 Mar 2022 05:26:06 +0000,
Oliver Upton <oupton@google.com> wrote:
> 
> Hi Marc,
> 
> On Mon, Mar 14, 2022 at 04:40:42PM +0000, Marc Zyngier wrote:
> > Since GICv4.1, it has become legal for an implementation to advertise
> > GICR_{INVLPIR,INVALLR,SYNCR} while having an ITS, allowing for a more
> > efficient invalidation scheme (no guest command queue contention when
> > multiple CPUs are generating invalidations).
> > 
> > Provide the invalidation registers as a primitive to their ITS
> > counterpart. Note that we don't advertise them to the guest yet
> > (the architecture allows an implementation to do this).
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/kvm/vgic/vgic-its.c     | 62 ++++++++++++++++++++----------
> >  arch/arm64/kvm/vgic/vgic-mmio-v3.c | 62 ++++++++++++++++++++++++++++++
> >  arch/arm64/kvm/vgic/vgic.h         |  4 ++
> >  include/kvm/arm_vgic.h             |  1 +
> >  4 files changed, 108 insertions(+), 21 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
> > index 089fc2ffcb43..cc62d8a8180f 100644
> > --- a/arch/arm64/kvm/vgic/vgic-its.c
> > +++ b/arch/arm64/kvm/vgic/vgic-its.c
> > @@ -1272,6 +1272,11 @@ static int vgic_its_cmd_handle_clear(struct kvm *kvm, struct vgic_its *its,
> >  	return 0;
> >  }
> >  
> > +int vgic_its_inv_lpi(struct kvm *kvm, struct vgic_irq *irq)
> > +{
> > +	return update_lpi_config(kvm, irq, NULL, true);
> > +}
> > +
> >  /*
> >   * The INV command syncs the configuration bits from the memory table.
> >   * Must be called with the its_lock mutex held.
> > @@ -1288,7 +1293,41 @@ static int vgic_its_cmd_handle_inv(struct kvm *kvm, struct vgic_its *its,
> >  	if (!ite)
> >  		return E_ITS_INV_UNMAPPED_INTERRUPT;
> >  
> > -	return update_lpi_config(kvm, ite->irq, NULL, true);
> > +	return vgic_its_inv_lpi(kvm, ite->irq);
> > +}
> > +
> > +/**
> > + * vgic_its_invall - invalidate all LPIs targetting a given vcpu
> > + * @vcpu: the vcpu for which the RD is targetted by an invalidation
> > + *
> > + * Contrary to the INVALL command, this targets a RD instead of a
> > + * collection, and we don't need to hold the its_lock, since no ITS is
> > + * involved here.
> > + */
> > +int vgic_its_invall(struct kvm_vcpu *vcpu)
> > +{
> > +	struct kvm *kvm = vcpu->kvm;
> > +	int irq_count, i = 0;
> > +	u32 *intids;
> > +
> > +	irq_count = vgic_copy_lpi_list(kvm, vcpu, &intids);
> > +	if (irq_count < 0)
> > +		return irq_count;
> > +
> > +	for (i = 0; i < irq_count; i++) {
> > +		struct vgic_irq *irq = vgic_get_irq(kvm, NULL, intids[i]);
> > +		if (!irq)
> > +			continue;
> > +		update_lpi_config(kvm, irq, vcpu, false);
> > +		vgic_put_irq(kvm, irq);
> > +	}
> > +
> > +	kfree(intids);
> > +
> > +	if (vcpu->arch.vgic_cpu.vgic_v3.its_vpe.its_vm)
> > +		its_invall_vpe(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe);
> > +
> > +	return 0;
> >  }
> 
> nit: the refactoring happening at the same time as the functional change
> is a bit distracting. Looks fine though.

Yeah, it didn't seem to warrant an extra patch, given that we're
really only moving things about.

> 
> >  /*
> > @@ -1305,32 +1344,13 @@ static int vgic_its_cmd_handle_invall(struct kvm *kvm, struct vgic_its *its,
> >  	u32 coll_id = its_cmd_get_collection(its_cmd);
> >  	struct its_collection *collection;
> >  	struct kvm_vcpu *vcpu;
> > -	struct vgic_irq *irq;
> > -	u32 *intids;
> > -	int irq_count, i;
> >  
> >  	collection = find_collection(its, coll_id);
> >  	if (!its_is_collection_mapped(collection))
> >  		return E_ITS_INVALL_UNMAPPED_COLLECTION;
> >  
> >  	vcpu = kvm_get_vcpu(kvm, collection->target_addr);
> > -
> > -	irq_count = vgic_copy_lpi_list(kvm, vcpu, &intids);
> > -	if (irq_count < 0)
> > -		return irq_count;
> > -
> > -	for (i = 0; i < irq_count; i++) {
> > -		irq = vgic_get_irq(kvm, NULL, intids[i]);
> > -		if (!irq)
> > -			continue;
> > -		update_lpi_config(kvm, irq, vcpu, false);
> > -		vgic_put_irq(kvm, irq);
> > -	}
> > -
> > -	kfree(intids);
> > -
> > -	if (vcpu->arch.vgic_cpu.vgic_v3.its_vpe.its_vm)
> > -		its_invall_vpe(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe);
> > +	vgic_its_invall(vcpu);
> >  
> >  	return 0;
> >  }
> > diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> > index 58e40b4874f8..186bf35078bf 100644
> > --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> > +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> > @@ -525,6 +525,59 @@ static void vgic_mmio_write_pendbase(struct kvm_vcpu *vcpu,
> >  			   pendbaser) != old_pendbaser);
> >  }
> >  
> > +static unsigned long vgic_mmio_read_sync(struct kvm_vcpu *vcpu,
> > +					 gpa_t addr, unsigned int len)
> > +{
> > +	return !!atomic_read(&vcpu->arch.vgic_cpu.syncr_busy);
> > +}
> > +
> > +static void vgic_make_rdist_busy(struct kvm_vcpu *vcpu, bool busy)
> 
> nit: s/make/set, since you use this helper to decrement the counter too.

Sure, works for me.

> > +{
> > +	if (busy) {
> > +		atomic_inc(&vcpu->arch.vgic_cpu.syncr_busy);
> > +		smp_mb__after_atomic();
> > +	} else {
> > +		smp_mb__before_atomic();
> > +		atomic_dec(&vcpu->arch.vgic_cpu.syncr_busy);
> > +	}
> > +}
> > +
> > +static void vgic_mmio_write_invlpi(struct kvm_vcpu *vcpu,
> > +				   gpa_t addr, unsigned int len,
> > +				   unsigned long val)
> > +{
> > +	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> > +	struct vgic_irq *irq;
> > +
> > +	if (!vgic_cpu->lpis_enabled)
> > +		return;
> > +
> > +	vgic_make_rdist_busy(vcpu, true);
> > +
> > +	irq = vgic_get_irq(vcpu->kvm, NULL, val);
> > +	if (!irq)
> > +		return;
> 
> Isn't the busy counter unbalanced if you return early?

Huh, well caught. Fix incoming.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
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