Re: [PATCH v6 15/24] KVM: arm64: vgic-its: Read config and pending bit in add_lpi()

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

On 05/05/17 10:57, Christoffer Dall wrote:
> On Thu, May 04, 2017 at 01:44:35PM +0200, Eric Auger wrote:
>> When creating the lpi we now ask the redistributor what is the state
>> of the LPI (priority, enabled, pending).
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>>
>> v6: creation
>> ---
>>  virt/kvm/arm/vgic/vgic-its.c | 35 ++++++++++++++++++++++++-----------
>>  1 file changed, 24 insertions(+), 11 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index f43ea30c..3ad615a 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -38,6 +38,8 @@
>>  
>>  static int vgic_its_set_abi(struct vgic_its *its, int rev);
>>  static const struct vgic_its_abi *vgic_its_get_abi(struct vgic_its *its);
>> +static int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
>> +			     struct kvm_vcpu *filter_vcpu);
>>  
>>  /*
>>   * Creates a new (reference to a) struct vgic_irq for a given LPI.
>> @@ -46,10 +48,12 @@ static const struct vgic_its_abi *vgic_its_get_abi(struct vgic_its *its);
>>   * If this is a "new" LPI, we allocate and initialize a new struct vgic_irq.
>>   * This function returns a pointer to the _unlocked_ structure.
>>   */
>> -static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid)
>> +static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
>> +				     struct kvm_vcpu *vcpu)
>>  {
>>  	struct vgic_dist *dist = &kvm->arch.vgic;
>>  	struct vgic_irq *irq = vgic_get_irq(kvm, NULL, intid), *oldirq;
>> +	int ret;
>>  
>>  	/* In this case there is no put, since we keep the reference. */
>>  	if (irq)
>> @@ -66,6 +70,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid)
>>  	irq->config = VGIC_CONFIG_EDGE;
>>  	kref_init(&irq->refcount);
>>  	irq->intid = intid;
>> +	irq->target_vcpu = vcpu;
>>  
>>  	spin_lock(&dist->lpi_list_lock);
>>  
>> @@ -97,6 +102,19 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid)
>>  out_unlock:
>>  	spin_unlock(&dist->lpi_list_lock);
>>  
>> +	/*
>> +	 * We "cache" the configuration table entries in out struct vgic_irq's.
> 
> s/out/our/ ?
> 
>> +	 * However we only have those structs for mapped IRQs, so we read in
>> +	 * the respective config data from memory here upon mapping the LPI.
>> +	 */
>> +	ret = update_lpi_config(kvm, irq, NULL);
>> +	if (ret)
>> +		return ERR_PTR(ret);
>> +
>> +	ret = vgic_v3_lpi_sync_pending_status(kvm, irq);
>> +	if (ret)
>> +		return ERR_PTR(ret);
>> +
>>  	return irq;
>>  }
>>  
>> @@ -769,6 +787,7 @@ static int vgic_its_cmd_handle_mapi(struct kvm *kvm, struct vgic_its *its,
>>  	u32 event_id = its_cmd_get_id(its_cmd);
>>  	u32 coll_id = its_cmd_get_collection(its_cmd);
>>  	struct its_ite *ite;
>> +	struct kvm_vcpu *vcpu = NULL;
>>  	struct its_device *device;
>>  	struct its_collection *collection, *new_coll = NULL;
>>  	int lpi_nr;
>> @@ -814,7 +833,10 @@ static int vgic_its_cmd_handle_mapi(struct kvm *kvm, struct vgic_its *its,
>>  	ite->collection = collection;
>>  	ite->lpi = lpi_nr;
>>  
>> -	irq = vgic_add_lpi(kvm, lpi_nr);
>> +	if (its_is_collection_mapped(collection))
>> +		vcpu = kvm_get_vcpu(kvm, collection->target_addr);
>> +
>> +	irq = vgic_add_lpi(kvm, lpi_nr, vcpu);
> 
> So, if we don't have the collection and therefore end up with irq->vcpu
> == NULL, how do we ever read the pending bit from memory as the affinity
> may later change?
> 
> Is this a problem with our idea of only looking at the pending bit on
> vgic_add_lpi, or does it just mean that we should sample the pending bit
> whenever we move LPIs around to VCPUs and if the bit is set, then also
> set the pennding_latch (if not already set), or what should happen here?

It means that we would need to sample that bit on MOVI and maybe MOVALL
as well, but this feels a bit odd. How did that bit land there the first
place?

Thanks,

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