Re: [Xen-devel] [PATCH v9 23/28] ARM: vITS: handle DISCARD command

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 22/05/17 18:20, Julien Grall wrote:
> 
> 
> On 22/05/17 17:50, Andre Przywara wrote:
>> Hi,
> 
> Hi Andre,
> 
>> On 18/05/17 15:23, Julien Grall wrote:
>>> Hi Andre,
>>>
>>> On 11/05/17 18:53, 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 | 24 ++++++++++++++++++++++++
>>>>  1 file changed, 24 insertions(+)
>>>>
>>>> diff --git a/xen/arch/arm/vgic-v3-its.c b/xen/arch/arm/vgic-v3-its.c
>>>> index ef7c78f..f7a8d77 100644
>>>> --- a/xen/arch/arm/vgic-v3-its.c
>>>> +++ b/xen/arch/arm/vgic-v3-its.c
>>>> @@ -723,6 +723,27 @@ 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);
>>>> +    int ret;
>>>> +
>>>> +    spin_lock(&its->its_lock);
>>>> +
>>>> +    /* Remove from the radix tree and remove the host entry. */
>>>> +    ret = its_discard_event(its, devid, eventid);
>>>> +
>>>> +    /* Remove from the guest's ITTE. */
>>>> +    if ( ret || write_itte_locked(its, devid, eventid,
>>>> +                                  UNMAPPED_COLLECTION, INVALID_LPI,
>>>> NULL) )
>>>
>>> I am not sure to fully understand this if. If ret is not NULL you
>>> override it and never call write_itte_locked.
>>
>> If its_discard_event() succeeded above, then ret will be 0, in which
>> case we call write_itte_locked(). If that returns non-zero, this is an
>> error and we set ret to -1, otherwise (no error) it stays at zero.
> 
> But we want to carry the error from its_discard_event. No?

Ah right, this was so cleverly made that I even tricked myself ;-)

I changed this now to be more easily readable.

Cheers,
Andre.

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