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

Auger Eric
2017-05-05T14:50:07Z

Hi,

On 05/05/2017 14:50, Marc Zyngier wrote:
> 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?

Without talking about save/restore, before this series the pending table
was sync'ed on RDIST LPI enable only and that's all. This is kept.

Now talking about save/restore, if we restore an LPI whose collection is
not attached to any RDIST, we can't sync at that time. The problem
exists if we check the pending bit on vgic_add_lpi or later, ie. at the
end of the ITS table restore process (as I did before). I don't see in
the spec we are supposed to read the pending table on MAPTI or MAPC.

Thanks

Eric
>
> Thanks,
>
> M.
>