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

Marc Zyngier
2017-05-05T12:50:18Z

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...