Re: [Xen-devel] [PATCH v8 23/27] ARM: vITS: handle INV command

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 12/04/17 18:20, Julien Grall wrote:
> Hi Andre,
> 
> On 12/04/17 01:44, Andre Przywara wrote:
>> The INV command instructs the ITS to update the configuration data for
>> a given LPI by re-reading its entry from the property table.
>> We don't need to care so much about the priority value, but enabling
>> or disabling an LPI has some effect: We remove or push virtual LPIs
>> to their VCPUs, also check the virtual pending bit if an LPI gets
>> enabled.
>>
>> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
>> ---
>>  xen/arch/arm/vgic-v3-its.c | 65
>> ++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 65 insertions(+)
>>
>> diff --git a/xen/arch/arm/vgic-v3-its.c b/xen/arch/arm/vgic-v3-its.c
>> index 09cb3af..f2789c5 100644
>> --- a/xen/arch/arm/vgic-v3-its.c
>> +++ b/xen/arch/arm/vgic-v3-its.c
>> @@ -418,6 +418,68 @@ static int update_lpi_property(struct domain *d,
>> uint32_t vlpi,
>>      return 0;
>>  }
>>
>> +/*
>> + * Checks whether an LPI that got enabled or disabled needs to change
>> + * something in the VGIC (added or removed from the LR or queues).
>> + * Must be called with the VCPU VGIC lock held.
>> + */
>> +static void update_lpi_vgic_status(struct vcpu *v, struct pending_irq
>> *p,
>> +                                   uint32_t vlpi)
> 
> p->irq should be equal to vlpi. No?

It is, by I liked the idea of having logically separate parameters
expressed as such. But I removed vlpi now and am using p->irq instead.

> 
>> +{
>> +    ASSERT(spin_is_locked(&v->arch.vgic.lock));
> 
> The locking is likely to wrong here too (see patch #2). For instance
> with a MOVI then INV on interrupt enabled.
> 
>> +
>> +    if ( test_bit(GIC_IRQ_GUEST_ENABLED, &p->status) )
>> +    {
>> +        if ( !list_empty(&p->inflight) &&
>> +             !test_bit(GIC_IRQ_GUEST_VISIBLE, &p->status) )
>> +            gic_raise_guest_irq(v, vlpi, p->lpi_priority);
>> +    }
>> +    else
>> +    {
>> +        clear_bit(GIC_IRQ_GUEST_ENABLED, &p->status);
>> +        list_del_init(&p->lr_queue);
>> +    }
>> +}
>> +
>> +static int its_handle_inv(struct virt_its *its, uint64_t *cmdptr)
>> +{
>> +    struct domain *d = its->d;
>> +    uint32_t devid = its_cmd_get_deviceid(cmdptr);
>> +    uint32_t eventid = its_cmd_get_id(cmdptr);
>> +    struct pending_irq *p;
>> +    unsigned long flags;
>> +    struct vcpu *vcpu;
>> +    uint32_t vlpi;
>> +    int ret = -1;
>> +
>> +    /* Translate the event into a vCPU/vLPI pair. */
>> +    if ( !read_itte(its, devid, eventid, &vcpu, &vlpi) )
>> +        return -1;
>> +
>> +    if ( vlpi == INVALID_LPI )
>> +        return -1;
>> +
>> +    spin_lock_irqsave(&vcpu->arch.vgic.lock, flags);
>> +
>> +    p = d->arch.vgic.handler->lpi_to_pending(d, vlpi);
>> +    if ( !p )
>> +        goto out_unlock;
> 
> As said on v5, this could be simpler and use the pending_irqs in the
> device. That would be an improvement though. So a would be good.

Originally I found it more straight-forward to use the one existing
interface (the rbtree) we also use in the VGIC part, which would allow
us to handle locking or ref-counting in one central place.
But indeed the ITS command handling has all the data we need to find the
pending_irq directly from the virtual device.
So I replaced all lpi_to_pending() calls in those handlers with a new
function gicv3_its_get_event_pending_irq(), which looks up the struct
from an ITS/device/event triple.
I take and keep the its->lock for the runtime of these functions, so
those events and their memory will not vanish meanwhile.

Does that make sense?

Cheers,
Andre.

>> +
>> +    /* Read the property table and update our cached status. */
>> +    if ( update_lpi_property(d, vlpi, p) )
>> +        goto out_unlock;
>> +
>> +    /* Check whether the LPI needs to go on a VCPU. */
>> +    update_lpi_vgic_status(vcpu, p, vlpi);
>> +
>> +    ret = 0;
>> +
>> +out_unlock:
>> +    spin_unlock_irqrestore(&vcpu->arch.vgic.lock, flags);
>> +
>> +    return ret;
>> +}
>> +
>>  static int its_handle_mapc(struct virt_its *its, uint64_t *cmdptr)
>>  {
>>      uint32_t collid = its_cmd_get_collection(cmdptr);
>> @@ -757,6 +819,9 @@ static int vgic_its_handle_cmds(struct domain *d,
>> struct virt_its *its)
>>          case GITS_CMD_INT:
>>              ret = its_handle_int(its, command);
>>              break;
>> +        case GITS_CMD_INV:
>> +            ret = its_handle_inv(its, command);
>> +            break;
>>          case GITS_CMD_MAPC:
>>              ret = its_handle_mapc(its, command);
>>              break;
>>
> 
> Cheers,
> 

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