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Re: [Xen-devel] [PATCH 2/3] evtchn: don't lose pending state if FIFO event array page is missing

  • To: Jan Beulich <JBeulich@xxxxxxxx>, David Vrabel <david.vrabel@xxxxxxxxxx>
  • From: Keir Fraser <keir.xen@xxxxxxxxx>
  • Date: Tue, 05 Nov 2013 21:07:52 +0000
  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 05 Nov 2013 21:08:27 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>
  • Thread-index: Ac7aaxbZUeYwtQmSg0OJZpwi6CrD1Q==
  • Thread-topic: [Xen-devel] [PATCH 2/3] evtchn: don't lose pending state if FIFO event array page is missing

On 04/11/2013 14:29, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

>>>> On 31.10.13 at 16:03, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>> From: David Vrabel <david.vrabel@xxxxxxxxxx>
>> When the FIFO-based ABI is in use, if an event is bound when the
>> corresponding event array page is missing any attempt to set the event
>> pending will lose the event (because there is nowhere to write the
>> pending state).
>> This wasn't initially considered an issue because guests were expected
>> to only bind events once they had expanded the event array, however:
>> 1. A domain may start with events already bound (by the toolstack).
>> 2. The guest does not know what the port number will be until the
>>    event is bound (it doesn't know how many already bound events there
>>    are), so it does not know how many event array pages are required.
>>    This makes it difficult to expand in advanced (the current Linux
>>    implementation expands after binding for example).
>> To prevent pending events from being lost because there is no array
>> page, temporarily store the pending state in evtchn->pending.  When an
>> array page is added, use this state to set the port as pending.
>> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

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