Re: [Xen-devel] [PATCH v5 25/30] ARM: vITS: handle DISCARD command

[Julien Grall <julien.grall@xxxxxxx>]

Hi Andre,

On 06/04/17 00:19, Andre Przywara wrote:
> The DISCARD command drops the connection between a DeviceID/EventID
> and an LPI/collection pair.
> We mark the respective structure entries as not allocated and make
> sure that any queued IRQs are removed.
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> ---
>  xen/arch/arm/vgic-v3-its.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/xen/arch/arm/vgic-v3-its.c b/xen/arch/arm/vgic-v3-its.c
> index 6afb915..47f2884 100644
> --- a/xen/arch/arm/vgic-v3-its.c
> +++ b/xen/arch/arm/vgic-v3-its.c
> @@ -549,6 +549,35 @@ out_unlock:
>      return ret;
>  }
>
> +static int its_handle_discard(struct virt_its *its, uint64_t *cmdptr)
> +{
> +    uint32_t devid = its_cmd_get_deviceid(cmdptr);
> +    uint32_t eventid = its_cmd_get_id(cmdptr);
> +    struct pending_irq *pirq;
> +    struct vcpu *vcpu;
> +    uint32_t vlpi;
> +
> +    if ( !read_itte(its, devid, eventid, &vcpu, &vlpi) )
> +        return -1;
> +
> +    pirq = its->d->arch.vgic.handler->lpi_to_pending(its->d, vlpi);
> +    if ( pirq )
> +    {
> +        clear_bit(GIC_IRQ_GUEST_QUEUED, &pirq->status);
> +        gic_remove_from_queues(vcpu, vlpi);
> +    }
Do we expect to have pirq returning NULL? If so, in which case?

Also, why not directly using

pirq = gicv3_assign_guest(....);

This would prevent the issue below where it would not be possible to 
write back in the guest memory, and leave the mapping with the host LPI.
> +
> +    if ( !write_itte(its, devid, eventid, UNMAPPED_COLLECTION, INVALID_LPI,
> +                     NULL) )
> +        return -1;
> +
> +    if ( !gicv3_assign_guest_event(its->d, its->doorbell_address,
> +                                   devid, eventid, NULL, 0) )
In which case gicv3_assign_guest_event can fail? And what would happen 
if it fails. By that I mean, would we need to carry some clean-up for 
host lpi during domain destruction?
> +        return -1;
> +
> +    return 0;
> +}
> +
>  #define ITS_CMD_BUFFER_SIZE(baser)      ((((baser) & 0xff) + 1) << 12)
>
>  /*
> @@ -580,6 +609,9 @@ static int vgic_its_handle_cmds(struct domain *d, struct 
> virt_its *its)
>          case GITS_CMD_CLEAR:
>              ret = its_handle_clear(its, command);
>              break;
> +        case GITS_CMD_DISCARD:
> +            ret = its_handle_discard(its, command);
> +            break;
>          case GITS_CMD_INT:
>              ret = its_handle_int(its, command);
>              break;
Cheers,

--
Julien Grall

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