Re: [PATCH 5/8] xen/evtchn: don't close the static event channel.

[Julien Grall <julien@xen.org>]

On 28/06/2022 14:53, Rahul Singh wrote:
> Hi Julien

Hi Rahul,

>> On 23 Jun 2022, at 4:30 pm, Julien Grall <julien@xen.org> wrote:
>>
>>
>>
>> On 23/06/2022 16:10, Rahul Singh wrote:
>>> Hi Julien,
>>>> On 22 Jun 2022, at 4:05 pm, Julien Grall <julien@xen.org> wrote:
>>>>
>>>> Hi,
>>>>
>>>> On 22/06/2022 15:38, Rahul Singh wrote:
>>>>> Guest can request the Xen to close the event channels. Ignore the
>>>>> request from guest to close the static channels as static event channels
>>>>> should not be closed.
>>>>
>>>> Why do you want to prevent the guest to close static ports? The problem I can see is...
>>> As a static event channel should be available during the lifetime of the guest we want to prevent
>>> the guest to close the static ports.
>> I don't think it is Xen job to prevent a guest to close a static port. If the guest decide to do it, then it will just break itself and not Xen.
> 
> It is okay for the guest to close a port, port is not allocated by the guest in case of a static event channel.
As I wrote before, the OS will need to know that the port is statically 
allocated when initializing the port (we don't want to call the 
hypercall to bind the event channel). By extend, the OS should be able 
to know that when closing it and skip the hypercall.

> Xen has nothing to do for close the static event channel and just return 0.

Xen would not need to be modified if the OS was doing the right (i.e. no 
calling close).

So it is still unclear why papering over the issue in Xen is the best 
solution.

Cheers,

-- 
Julien Grall